XII IP CBSE 4-6

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BASICS OF OBJECT
ORIENTED PROGRAMMING
Learning Objectives




4 Puzzle
After studying this lesson the students will be able to:
Understand the need of object oriented programming
Define the various terms related to object oriented programming
Identify the features of an object oriented programming language
Use features of object oriented programming language to develop simple
applications
Over the last lesson, we have reviewed the core Java language. We have learnt
how to work with variables and data, perform operations on that data, make
decisions based on the data and also loop repeatedly over the same section of
code. Now we will move on to learn a concept that is central to Java, namely
Object Oriented Programming. Object Oriented Programming is a very user
friendly yet a powerful approach to solve basic to difficult problems. The idea
was created for developing a language that could be used for system
description (for people) and system prescription (as a computer program
through a compiler). There are several object-oriented languages. The three
most common ones are, Smalltalk, C++ and Java.
A student and a lady are travelling in a train. They get around talking and the lady decides
to give a puzzle to the student. She tells him that she has 3 children whose product of ages
is equal to the maximum number of runs possible to score in an over without any
illegitimate ball being bowled (i.e. NB, Wide, etc). Also, the sum of their ages is equal to
her berth number. However, the student isn’t able to answer. The lady then gives him a
further hint that the eldest of her children has only one eye. At this information, the
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student knows the ages of the three children. Without knowing the lady’s berth number,
can you guess the ages of her children?
James Alexander is a resident of a developed nation and works as a freelance consultant.
He is hired by one of the corporate houses of a developing nation to plan a strategy to
improve production in one of their factories which is located in a remote village named
Khabri. The consultant decides to submit a quick action plan and so starts searching for
information about the remote village. He has never visited any of the remote locations
and so tries to simply imagine the problems faced by remote people. Mohan Swamy is a
resident of one of the developing countries and he also is a freelance consultant. He
completed his studies from a top notch university and to actually put his theoretical
knowledge to practice, he started staying in the remote village Khabri. He wanted to
actually experience the hardships faced by people residing in remote areas. To sustain
himself he decides to pick up a job in the only factory situated in Khabri. The HR manager
impressed with his in-depth knowledge and qualifications requests him to also plan a
strategy to improve production of their factory. Who do you think will be able to provide a
more viable solution? The obvious answer for most of us would be that the person sitting
in the remote village and literate enough to solve the problem will be able to provide a
better strategy because he closely understands the real problems of the residents as
compared to a person sitting far away. But what does this teach us about programming?
This teaches us that in programming also
Introduction
functions/methods/programs written for
specific situations are able to manipulate data of their respective entities more
efficiently. Now, let us understand a little about the various programming paradigms.
Computer programming is a process of designing, writing, testing, debugging and
maintaining the source code of computer programs written in a particular programming
language. The purpose of programming is to organize instructions that are capable of
solving real life problems. The process of writing source code of programs requires
expertise in subject, knowledge of desired application domain, a formal logic and
knowledge of syntax of the relevant programming language. Writing instructions in the
desired order gives the required results from the program but when these instructions
Introduction to Programming
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BASICS OF OBJECT ORIENTED PROGRAMMING
increase in number, it becomes extremely difficult for the programmer to debug,
maintain or troubleshoot codes. For this reason, technology experts kept developing and
introducing different programming paradigms and accordingly kept developing
languages to support these paradigms. Procedural programming paradigm was one of the
major stepping stone for these experts which focused on breaking down a programming
task into a collection of small modules known as sub routines or procedures. This
paradigm helped the programmers to debug, maintain or troubleshoot codes in a more
effective manner. The experts did not stop their research in improving this paradigm and
introduced a new paradigm known as object oriented programming paradigm where a
programming task was broken into objects. Here each object was capable of
encapsulating its own data and methods (subroutines / procedures). The most important
distinction is that where procedural programming uses procedures to operate on data,
object oriented programming bundles data and methods together and operates as a
independent entity of the program. Some languages support one particular programming
paradigm while some are developed to support multiple programming paradigms. C++, C
sharp, Object Pascal etc. are the languages which support procedural as well as object
oriented paradigm. Java supports only object oriented programming. Basic, COBOL
support only procedural programming.
Object Oriented Programming follows bottom up approach in program design and
emphasizes on safety and security of data. It helps in wrapping up of data and methods
together in a single unit which is known as data encapsulation. Object Oriented
Programming allows some special features such as polymorphism and inheritance.
Polymorphism allows the programmer to give a generic name to various methods or
operators to minimize his memorizing of multiple names. Inheritance enables the
programmer to effectively utilize already established characteristics of a class in new
classes and applications.
The major components of Object Oriented Programming are as follows:
1. Class
2. Object
Object Oriented Programming
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3. Data Members & Methods
4. Access Specifier and Visibility Modes
A class is used to encapsulate data and methods together in a single unit. It helps the
programmer to keep the data members in various visibility modes depending upon what
kind of access needs to be provided in the remaining part of the application. These
visibility modes are classified as private, public and protected. Usually, data members of
a class are kept in private or protected visibility modes and methods are kept in the public
visibility mode.
An object is an instance of a class that is capable of holding actual data in memory
locations.
Class and objects are related to each other in the same way as data type and variables.
For example, when we declare float variable named marks, the variable marks can be
thought of as an object of type float which can be assumed as the class. If we take another
hypothetical case in which Human is a class, Mr. Arun Shah, Mr. Aneek Ram will be the
objects of this Human class.
We have already learnt that a class contains data members and methods. As discussed in
the above example, Mr.Arun Shah is an object of class Human. The phone numbers
retained by Mr.Arun Shah in his brain (memory) will be the data. His eyes, ears, nose and
mouth can be considered as various methods which allow Mr.Arun Shah to collect, modify
and delete data from his memory.
In real java programming, this data will be required to conform to a specific data type as
in char, int, float or double whereas the methods will be a sequence of steps written
together to perform a specific task on the data. Carefully observe the illustration given in
Figure 4.1 to reinstate the theoretical concepts learnt above.
Classes and Objects :
Data Members and Methods :
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Figure 4.1 Illustration Showing the Class, Object, Members and Methods
Referring to the situation presented in the introduction of the chapter, just like the
person residing in the village can efficiently solve problems pertaining to his village,
similarly the methods of specific classes are able to manipulate data of their respective
classes efficiently resulting in better security of data in an Object Oriented Programming
paradigm.
Now that you are clear about the concept of a class and an object, you will be able to
appreciate and identify classes and methods that we have already been using throughout
our class XI. Do you know JTextField, JLabel, JTextArea, JButton, JCheckBox and
JRadioButton are all classes and the jTextField1, jLabel1, jTextArea1, jButton1,
jCheckBox1 and jRadioButton1 components are all objects. The setText(), setEnabled(),
pow(), substring() are all methods of different classes. This concept is illustrated in
Figure 4.2.
Class Employee
Data Members



EmpNo
Name
Salary
Method



AddNewEmployee()
DisplayEmployee()
CalculateSalary()
Object Employee 1



1001
Arun Shah
38000
Object Employee 2



1002
Aneek Ram
49000
Object Employee 3



1007
Kamya Sarkar
32000
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Figure 4.2 JTextField and JLabel Classes
Notice that the properties like Text, Enabled, Editable are actually the data
members in the class because they store specific values as data. For example
the property Text of jTextField1object contains the actual text to be
displayed in the text field.
Class
JTextField
Data Members




Text
Editable
Enabled
toolTipText
Method





setText()
getText()
setEditable()
setEnabled()
setToolTipText()
Object 1




“Amit Khanna”
true
false
“Enter Name”
jTextField1
Object 2




“Indian”
false
false
“Citizenship”
jTextField2
Class
JLabel
Data Members



Text
Editable
toolTipText
Method




setText()
getText()
setToolTipText()
setEnabled()
Object 1



“Age”
(21-62 Years)
True
jLabel1
Object 2



“Gender”
(Male/Female)
True
jLabel2
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The following two tables summarize the data members (properties) and methods of all
classes learnt during the course till now:
JTextField jTextField1 Text setText()
Editable getText()
Enabled setEditable()
ToolTipText setEnabled()
setToolTipText()
JLabel jLabel1 Text setText()
Enabled getText()
ToolTipText setEnabled()
setToolTipText()
JTextArea jTextArea1 Columns isEditable()
Editable isEnabled()
Font getText()
lineWrap setText()
Rows
wrapStyleWord
toolTipText
JButton jButton1 Background getText()
Enabled setText()
Font
Foreground
Text
Label
Class Objects Data Members Methods
(Properties)
• •
• •
• •
• •

• •
• •
• •

• •
• •
• •
• •



• •
• •




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JCheckBox jCheckBox1 Button Group getText()
Font setText()
Foreground isSelected()
Label setSelected()
Selected
Text
JRadioButton jRadioButton1 Background getText()
Button Group setText()
Enabled isSelected()
Font setSelected()
Foreground
Label
Selected
Text
JPasswordField jPasswordField1 Editable setEnabled()
Font setText()
Foreground getText()
Text isEnabled()
Columns
toolTipText
JComboBox jComboBox1 Background getSelectedItem()
ButtonGroup getSelectedIndex()
Editable setModel()
Enabled
• •
• •
• •
• •


• •
• •
• •
• •




• •
• •
• •
• •


• •
• •
• •

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Font
Foreground
Model
SelectedIndex
SelectedItem
Text
JList jList1 Background getSelectedValue()
Enabled
Font
Foreground
Model
SelectedIndex
SelectedItem
SelectionMode
Text
JTable jTable1 model addRow()
getModel()
It is the ability of a method to execute in many forms. In object oriented programming
there is a provision by which an operator or a method exhibits different characteristics
depending upon different sets of input provided to it. This feature in Object Oriented
Programming is known as polymorphism. Two examples of polymorphism are method
overloading and operator overloading. Method overloading is where a method name can
be associated with different set of arguments/parameters and method bodies in the
same class. The round() method of the Math class and the substring() method of the String
class are good examples of method overloading. The following examples explain how
round() and substring() methods are overloaded.






• •








• •

Polymorphism :
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If the argument passed to the round() method is of type double then it rounds off the
double value and returns the closest long value. On the other hand, if the argument
passed to the round() method is of type float then it rounds off the float value and returns
the closest integer value. This simply means that the round() method is overloaded on the
basis of the type of arguments supplied to it. Figure 4.3 illustrates the concept of method
overloading as demonstrated by the round()method. For example:
float f = 12.5;
double d = 123.6543;
int num1 = Math.round(f); //num1 will store 13
float num2 = Math.round(d); //num2 will store 124.0
Notice that if the argument is of type double and we try to round it to an integer,
then it results in an error because no such method is pre-defined which takes a
double argument and rounds it to integer type.
Figure 4.3 Polymorphism demonstrated by round() method
If a single argument is passed to the substring() method then it returns all characters from
the start position to the end of the string whereas if two arguments are passed to the
substring() method then it returns a substring of the characters between the two
specified positions of the string. This simply means that the substring() method is
overloaded on the basis of the number of arguments supplied to it. For example:
String Message = “Good Morning”, Message1, Message2;
Message1 = Message.substring(5);//Message1 will store Morning
Message2 = Message.substring(0,4); //Message2 will store Good
Math.round()
Math.round()
float
double
int
float
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Operator Overloading is another example of polymorphism. Just as methods can be
overloaded, operators can also be overloaded. A very good example of operator
overloading is the + operator which returns the sum of two numbers if the operands are
numbers but returns the concatenated string if the operands are characters or strings.
For example:
String A = “Hello”, B = “There”;
String C = A + B; //C will store HelloThere
int num1 = 10, num2 = 20;
int num3 = num1 + num2; //num3 will store 30
The classes for which objects are required to be
declared are known as concrete classes like JLabel,
JTextField, JComboBox etc. The classes for which it is
not essential to declare objects to use them are known
as abstract classes like JOptionPane. Abstract classes
are normally used as base class in inheritance for
which no direct object is required to be created. Also
abstract classes are used for defining generic methods
where there is no requirement of storing results.
Notice that the JOptionPane Class which is an abstract class has no data members
and so it will not be able to store any values. The reason behind this is that
because we cannot create objects of an abstract class, so we will not be able to
provide any data to this class. Therefore, there is no point of having a data
member.
Inheritance is the most powerful feature of Object Oriented Programming, after classes
themselves. Inheritance is a process of creating new class (derived class or sub class or
child class) from existing class (base class or super class or parent class). The derived
classes not only inherit capabilities of the base class but also can add new features of
Abstract Class :
Inheritance :
Abstract Class



showMessageDialog()
showingputDialog()
showConfirmDialog()
JOptionPane
Methods
Figure 4.4
Example of an Abstract Class
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their own. The process of Inheritance does not affect the base class. Observe the base
and the derived class shown in Figure 4.5 carefully. Notice that the derived class inherits
the data members namely Colour and Height from the base class and has a new data
member defined in itself namely the Type. Similarly the derived class inherits the
methods namely getColour() and getHeight() from the base class and has a new method
defined in itself namely the setType().
Figure 4.5 Concept of Base Class and Derived Class
The most important aspect of inheritance is that it allows reusability of code, and also a
debugged class can be adapted to work in different situations. Reusability of code saves
money as well as time and increases program reliability. Inheritance is very useful in
original conceptualization and design of a programming problem. The idea of inheritance
helps you to include features of already existing class (debugged) in a new class.
Properties (data members) and methods included in super class can be invoked/accessed
from the subclass. A subclass inherits all the members (data members and methods) from
its superclass.
Figure 4.6 Common Examples of Inheritance
PERSON
EMPLOYEE
VEHICLE
CAR
Vehicle
getColour()
getHeight()
Colour
Height
Car
(Inherits all data members of class Vehicle)
Type
(Inherits all methods of class Vehicle)
setType
Base Class
(Super Class)
Derived Class
(Sub Class)
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The new class can, in turn, can serve as the basis for another class definition. It is
important to know that all Java objects use inheritance and every Java object can trace
back up the inheritance tree to the generic class Object.
If you look at the pre-fabricated code (code automatically added by the compiler) in any
of your application (JFrame Form) created in NetBeans, you will observe that
javax.swing.JFrame acts as a base class (super class) and the name given by you for the
JFrame Form acts as the name for the derived class (sub class). Each new JFrame Form
added to the application inherits all the features of the javax.swing.JFrame class. The
screen shot from one such application is shown below to illustrate the same. Here,
javax.swing.JFrame is the base class and Example is the derived class.
public class Example extends javax.swing.JFrame
{
/** Creates new form named Example */
public Example()
{
initComponents();
}
}
Figure 4.7 Sample Code Illustrating the Concept of Inheritance in Java
Notice that the extends keyword is used to inherit data members and methods of
the JFrame base class for the Example class which is the derived class.
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Summary











Procedural programming paradigm focuses on breaking down a programming
task into a collection of small modules known as sub routines or procedures.
The most important distinction between Procedural and Object Oriented
Programming is that where Procedural Programming paradigm uses procedures
to operate on data, Object Oriented Programming paradigm bundles data and
methods together and operates as an independent entity of the program.
Class, object, data members and methods are the major components of an
Object Oriented Programming paradigm.
A class is used to encapsulate data and methods together in a single unit and an
object is an instance of a class.
Polymorphism is the ability of a method to execute in many forms.
Method overloading and operator overloading are two examples of
Polymorphism.
The round() method of the Math class and the substring() method of the String
class are good examples of method overloading.
The + operator is a good example of operator overloading in Java.
The classes for which it is not essential to declare objects to use them are
known as abstract classes. JOptionPane is one of the examples of an abstract
class.
The concept of Inheritance allows reusability of code by including features of
already existing class (called the base class) in a new class (called the derived
class).
The extends keyword is used to inherit data members and methods of the base
class and allows the derived class to use these methods.
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EXERCISES
MULTIPLE CHOICE QUESTIONS
1. Which of the following is not a feature of Object Oriented Programming?
a. Inheritance b. Data Overloading
c. Polymorphism d. Objects
2. Identify which of the following are not valid examples of method overloading?
a. round() b. subString()
c. subStr() d. getText()
3. Which of the following statements about the Java language is true?
a. Both procedural and OOP are supported in Java
b. Java supports only procedural approach
c. Java supports only OOP approach
d. None of the above
4. Which of the following is an Abstract class?
a. JTextArea b. String
c. Math d. JFrame
5. Which of the following statements is false about objects?
a. Object is an instance of a class
b. Object is capable of storing data
c. Each object has its own copy of methods
d. None of the above
6. A class can have many methods with the same name as long as the number of
parameters or type of parameters is different. This OOP concept is known as
a. Method Overriding b. Method Overloading
c. Method Invocating d. Method Labelling
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7. Which of the following statement is true?
a. A super class is a subset of a sub class
b. class Second extends First means First is a sub class
c. class Second extends First means Second is a super class
d. None of the above
8. Which feature(s) of Object Oriented Programming is illustrated in the following
code snippet:
String A = “Hello”, B = “There”, C;
String C = A + B;
int num1 = 10, num2 = 20;
int num3 = num1 + num2;
C = B.substring(1);
B = A.substring(3);
a. Method Overloading b. Inheritance
c. Operator Overloading d. None of the above
1. Define the term Polymorphism. What are the two ways polymorphism is
demonstrated in Java?
2. What is the importance of abstract classes in programming?
3. Write a short note on Operator overloading and Method Overloading citing examples
for both.
4. Carefully study the code given below. It is giving an error whenever it is compiled:
float f = 12.5;
double d = 123.6543;
ANSWER THE FOLLOWING QUESTIONS
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int num1 = Math.round(f); //Statement 1
float num2 = Math.round(d); //Statement 2
int num2 = Math.round(d); // Statement 3
Identify the statement that will result in an error. Justify.
5. Carefully study the code given below:
String Message = “Hello! How are you?”, Msg1, Msg2;
Msg1 = Message.substring(7);
Msg2 = Message.substring(0,5);
What will be the contents of the variables Msg1 and Msg2 after the above statements
are executed?
6. Study the following code and answer the questions that follow:
String SMS=jTextArea1.getText();
int L=SMS.length(),Balance;
Balance=160-L;
jTextField2.setText(Integer.toString(L));
jTextField3.setText(Integer.toString(Balance));
a. Name any one native class of Java used in the above code.
b. Name the object created of the above mentioned native class.
c. Identify and name two methods of the native class.
d. Name the method used to convert one type of data to another and also mention
the data type before and after conversion.
7. Study the following code and answer the questions that follow:
public class Example extends javax.swing.JFrame
{
/** Creates new form named Example */
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public Example()
{
initComponents();
}
}
a. Which feature of object oriented programming is depicted above?
b. Name the base class and the derived class.
c. Name the keyword used for passing on characteristics of the base class to
derived class.
8. Compare and contrast the Procedural Programming paradigm and the Object
Oriented Programming paradigm by writing a simple program of a mathematical
calculator using both approaches. (Note: The teacher may illustrate the Procedural
Programming Paradigm using any other simple programming language but should
not test the students on it).
1. Create a GUI application to accept a string and display it in reverse order using the
substring() method.
2. Create a GUI application to create random whole numbers between 2 float numbers
input by the user.
3. Create a GUI application to accept 3 numbers in separate text fields and display
their sum, average, maximum or minimum after rounding the results on the click of
appropriate buttons (There are four separate buttons – one for sum, one for
average, one for maximum and one for minimum). The result should be displayed in
the fourth text field.
4. Create a GUI application to accept the date (as 1), month (as a number like 3 for
March) and year (as 2010) in separate text fields and display the date in the format:
dd/mm/yy. Take care of the following points while creating the application:
† LAB EXERCISES
† The students should be encouraged to design appropriate forms for the applications themselves.
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Verify the date input before displaying it in the suggested format and display
error messages wherever applicable
The date is accepted as 1 (for the first of any month) but should be displayed as
01 in the final format.
The year is accepted as 2010 but displayed as 10 in the final format.
(Team size recommended: 3 students each team)
1. Divide the class into 6 groups. Assign one class (out of JTextField, JTextArea, JLabel,
JCheckbox, JRadioButton and JComboBox) to each of the groups and instruct each
group to create applications demonstrating the usage of all methods learnt of that
particular class. The groups may also enhance the forms using different properties
of the assigned classes.
2. Divide the class into three groups and tell each group to create presentations on one
of the following topics (The topics may be allocated using a draw system):
a) Programming Paradigms
b) The Philosophy of Object Oriented Programming
c) Future Trends in Programming



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PROGRAMMING CONCEPTS
Learning Objectives





5 Puzzle
After studying this lesson the students will be able to:
Define objects and their usage
Appreciate the usage of native classes Math and String
Understand the need and use of methods pow() and round() of Math class
Understand the need and use of methods toUpperCase(),
toLowerCase(),substring(), concat(), length() and trim() of String class
Develop small applications involving the methods learnt of Math and String
classes.
In the last lesson, we introduced the concept of Object Oriented Programming and
learnt about the different elements of an Object Oriented Programming
Language. Now we will move on to learn about two important classes we
commonly use in Java – namely Math and String. The lesson focuses on how to use
some of the popular methods of these classes appropriately and appreciate how
they simplify many programming tasks for us.
Find a 9-digit number, which you will gradually round off starting with the number placed
at units, then tens, hundreds etc., until you get to the last numeral, which you do not
round off. The rounding alternates (down, up, down …) which means that the first
number from the right is rounded down while the second number from the right is
rounded up and so on. After rounding off 8 times, the final number is 500000000. The
original number is commensurable by 6 and 7, all the numbers from 1 to 9 are used, and
after rounding four times the sum of the not rounded numerals equals 24.
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Classes and Objects
Math Class
As studied in the previous lesson, a class is used to encapsulate data and methods
together in a single unit. An object is an instance of a class that is capable of holding
actual data in memory locations. Class and objects are related to each other in the same
way as data type and variables. If we take a hypothetical case in which human is a class,
Mr. Shah and Mr. Kumar will be the objects of this Human class.
The Math class contains built-in methods for performing basic numeric operations such as
the elementary exponential, rounding of a number, square root, and trigonometric
functions. These functions can be used directly by the user in the program. These
methods are highly reliable and can tremendously reduce the amount of coding required
for an application.
Some of the most commonly used Math class methods are as follows:
pow(double a, double b) Returns the value of the first argument raised to the
second argument.
round(double a) Returns the closest long to the double argument.
round(float a) Returns the closest int to the float argument.
It is not necessary to import any package for the Math class because this is already in the
java.lang package. Therefore in-built methods of the Math class can be used directly in
the application just like the other methods, as we have learnt in the previous class. Let us
learn the usage of these methods by building some simple applications. First let us create
an application that calculates the power of a number. Observe the following form
carefully.
Method Description
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ADVANCED PROGRAMMING CONCEPTS
Figure 5.1 Sample Run of the Raised to Power Application
Let us first design the form as shown in Figure 5.1. First add a new JFrame form and set its
title property to “Raised to Power”. Now, add the following components on the form:
Two editable text fields to accept the number and the power
One non-editable text field to display the calculated result
Two buttons – one to calculate & display the result and one to reset the form
components
Three appropriate labels – one against each of the text field to direct the user.
Change the properties of the components as learnt earlier so that the form looks exactly
like the one displayed in Figure 5.1. The next step is to associate code with both the
buttons. Double click on the buttons one by one in the design window to reach the point in
the source window where the code needs to be written. Add the code for each of the
buttons as given in Figure 5.2.
private void
jButton1ActionPerformed(java.awt.event.ActionEvent evt)
{
// Calculate the value of NumberRaise using the pow()
function




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double Number,Raise,Result;
Number=Double.parseDouble(jTextField1.getText());
Raise=Double.parseDouble(jTextField2.getText());
Result=Math.pow(Number, Raise);
jTextField3.setText(Double.toString(Result));
}
private void
jButton2ActionPerformed(java.awt.event.ActionEvent evt)
{
// Clear all text fields by initializing them with blank
spaces
jTextField1.setText(“”);
jTextField2.setText(“”);
jTextField3.setText(“”);
}
Figure 5.2 Code for the Raised to Power Application
Let us now understand the code in detail line by line:
double Number,Raise,Result;
Declare three variables named Number, Raise and Result of type double.
Number=Double.parseDouble(jTextField1.getText()); and
Raise=Double.parseDouble(jTextField2.getText());
Retrieve the values input by the user from the text fields using the method
getText() and store these values in the variables Number and Raise
respectively.


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ADVANCED PROGRAMMING CONCEPTS
Result=Math.pow(Number, Raise);
Calculate the number (value stored in variable Number) raised to the value
stored in the variable Raise using the pow() method and store the final value in
the variable Result.
jTextField3.setText(Double.toString(Result));
Display the final result in the third text field using the setText() method after
converting it to string type using the toString() method.
Next, let us give a quick look to the coding of the RESET button:
jTextField1.setText(“”); and
jTextField2.setText(“”); and
jTextField3.setText(“”);
The display text of all the three buttons is set to an empty string (i.e. blank)
using the setText() method.
Next let us learn the usage of another method of the Math class namely round(). Observe
the following form carefully.
Figure 5.3 Design of the Number Rounding Off Application
Let us first design the form as shown in Figure 5.3. First add a new JFrame form and set its
title property to “Number Rounding Off”. Now, add the following components on the form:
One editable text field to accept the number to be rounded.
One non-editable text field to display the rounded off number





127
ADVANCED PROGRAMMING CONCEPTS
Four radio buttons -to give a choice to the user for rounding off the number
upto 0, 1, 2 or 3 digits
Three labels – one against each of the text field and one against the radio
button group to appropriately direct the user.
Change the properties of the components so that the form looks exactly like the one
displayed in Figure 5.3. The next step is to associate code with the radio buttons. Double
click on the buttons one by one in the design window to reach the point in the source
window where the code needs to be written. Add the code for each of the buttons as given
in Figure 5.5. A sample run of the application is shown in Figure 5.4.
Figure 5.4 Sample Run of the Number Rounding Application
private void
jRadioButton1ActionPerformed(java.awt.event.ActionEvent evt)
{ //to round off the input number
double Number,RoundedNumber;
Number=Double.parseDouble(jTextField1.getText());
RoundedNumber=Math.round(Number);
jTextField2.setText(Double.toString(RoundedNumber));
}


128
ADVANCED PROGRAMMING CONCEPTS
private void
jRadioButton2ActionPerformed(java.awt.event.ActionEvent evt)
{ //to round off the number to 1 digit
double Number,RoundedNumber;
Number=Double.parseDouble(jTextField1.getText());
//You need to divide by a real number and so 10.0 and
not 10
RoundedNumber=Math.round(Number*10)/10.0;
jTextField2.setText(Double.toString(RoundedNumber));
}
private void
jRadioButton3ActionPerformed(java.awt.event.ActionEvent evt)
{ //to round off the number to 2 digits
double Number,RoundedNumber;
Number=Double.parseDouble(jTextField1.getText());
RoundedNumber=Math.round(Number*100)/100.0;
jTextField2.setText(Double.toString(RoundedNumber));
}
private void
jRadioButton4ActionPerformed(java.awt.event.ActionEvent evt)
{ //to round off the number to 3 digits
double Number,RoundedNumber;
Number=Double.parseDouble(jTextField1.getText());
RoundedNumber=Math.round(Number*1000)/1000.0;
jTextField2.setText(Double.toString(RoundedNumber));
}
Figure 5.5 Code for the Number Rounding Application
129
ADVANCED PROGRAMMING CONCEPTS
Let us now understand the code in detail line by line:
double Number,RoundedNumber;
Declare two variables named Number and RoundedNumber of type double.
Number=Double.parseDouble(jTextField1.getText());
Retrieve the value input by the user in the first text field using the getText()
method and store it in the variable Number after converting it to type double
(using the parseDouble() method)
RoundedNumber=Math.round(Number*10)/10.0;
Calculate the rounded number using the round method and store it in the
variable RoundedNumber. Since the round method does not allow the user to
specify the precision digits, so we first multiply the number by 10 (for rounding
off to 1 digit and similarly multiply by 100 for rounding off to 2 digits and so on)
and then divide the result by 10 to get the closest double number.
jTextField2.setText(Double.toString(RoundedNumber));
Display the calculated result in the second text field using the setText()
method after converting it to type String using the toString() method.
The coding for the other radio buttons is similar.
Next let us learn a few methods of another important class, namely String class, of Java.
The String class includes methods for examining individual characters of a string
sequence, for converting strings to uppercase or lowercase, for extracting substrings, for
joining two strings together, for calculating the length of a string and also for creating a
new string by omitting the leading and trailing whitespaces.
When using most of the String class’s methods, it should be kept in mind that a string is
just a series of individual characters and that each character has a position or index, a
little like a queue. Remember that in strings the first position, or index, is labelled 0 and
not 1. So, if we create a string “HAPPY” then the characters will be stored as shown below:




String Class :
130
ADVANCED PROGRAMMING CONCEPTS
Character Index 0 1 2 3 4
Character stored H A P P Y
Some of the String class methods are as follows:
concat(String str) Concatenates the specified string to the end of this
string.
length() Returns the length of the string.
substring (int beginpos Returns a substring of the characters between the two
[, int endpos]) specified positions of the string. The second parameter
is optional; if not included then all characters from the
start position to the end of the string are included. The
character at the ending position (n2) is not included.
toLowerCase() Returns the string converted to lower case.
toString() Returns the object as a string.
toUpperCase() Returns the string converted to upper case.
trim() Returns the string, after removing the leading and the
trailing whitespaces
The most important methods are case conversion methods toUpperCase() and
toLowerCase(), so let us first develop a “Case Changer” application. Observe the following
form carefully:
Figure 5.6 Sample Execution of the Case Changer Application
Method Description
131
ADVANCED PROGRAMMING CONCEPTS
Let us first design the form as shown in Figure 5.6. First add a new JFrame form and set its
title property to “Case Changer”. Now, add the following components on the form:
One editable text field to accept the string to be converted to uppercase and
lowercase
Two non-editable text fields – one to display the string converted to uppercase
and the other to display the string converted to lowercase
Two buttons – one to convert & display the converted strings and one to reset
the form components
Three appropriate labels – one against each of the text field to direct the user.
Change the properties of the components so that the form looks exactly like the one
displayed in Figure 5.6. The next step is to associate code with both the buttons. Double
click on the buttons one by one in the design window to reach the point in the source
window where the code needs to be written. Add the code for each of the buttons as
given in Figure 5.7.
private void
jButton1ActionPerformed(java.awt.event.ActionEvent evt)
{
//Convert an input string to lower case and upper case
String Str=jTextField1.getText();
jTextField2.setText(Str.toLowerCase());
jTextField3.setText(Str.toUpperCase());
}




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ADVANCED PROGRAMMING CONCEPTS
private void
jButton2ActionPerformed(java.awt.event.ActionEvent evt)
{ // Clear all text fields by initializing them with blank
spaces
jTextField1.setText(“”);
jTextField2.setText(“”);
jTextField3.setText(“”);
}
Figure 5.7 Code for the Case Changer Application
Let us now understand the code in detail line by line:
String Str=jTextField1.getText();
Declare a variable named Str of type String and initialize it with the value input
by the user in the first text field. The value entered in the text field is retrieved
using method getText().
jTextField2.setText(Str.toLowerCase());
Convert the string named Str to lower case using the toLowerCase() method
and then display the converted string in the second text field using the
setText() method.
jTextField3.setText(Str.toUpperCase());
Convert the string named Str to upper case using the toUpperCase() method
and then display the converted string in the third text field using the setText()
method.
The coding of the RESET button is exactly the same as learnt in the earlier examples.
Now that we know how to use the methods of the String class, let us next learn two more
new methods – one to extract specified number of characters from a string and next to
join two strings together. To learn these two methods, let us design an application called



133
ADVANCED PROGRAMMING CONCEPTS
Short Name. The aim of the application is to accept the First Name, Middle Name and the
Last Name from the user and display his short name (i.e Last Name followed by his
initials). Observe the following form carefully.
Figure 5.8 Sample Run of the Short Name Application
Let us first design the form as shown in Figure 5.8. First add a new JFrame form and set its
title property to “Short Name”. Now, add the following components on the form:
Three editable text fields to accept the first, middle and last name from the
user
One non-editable text field to display the short name
Two buttons – one to convert & display the short name and one to reset the form
components
Four labels – one against each of the text field to appropriately direct the user.
Change the properties of the components so that the form looks exactly like the one
displayed in Figure 5.8. The next step is to associate code with both the buttons. Double
click on the buttons one by one in the design window to reach the point in the source
window where the code needs to be written. Add the code for each of the buttons as given
in Figure 5.9.




134
ADVANCED PROGRAMMING CONCEPTS
private void
jButton1ActionPerformed(java.awt.event.ActionEvent evt)
{
// To convert a full name to a short name
String FirstName,MiddleName,LastName,ShortName=””;
FirstName=jTextField1.getText().substring(0,1);
MiddleName=jTextField2.getText().substring(0,1);
LastName=jTextField3.getText();
ShortName=ShortName.concat(LastName);
ShortName=ShortName.concat(” “); // to add a blank space
ShortName=ShortName.concat(FirstName);
ShortName=ShortName.concat(“.”); // to add a dot to
separate FN and MN
ShortName=ShortName.concat(MiddleName);
ShortName=ShortName.concat(“.”);
jTextField4.setText(ShortName);
}
private void
jButton2ActionPerformed(java.awt.event.ActionEvent evt)
{
// Clear all text fields by initializing them with blank
spaces
jTextField1.setText(“”);
jTextField2.setText(“”);
jTextField3.setText(“”);
jTextField4.setText(“”);
}
Figure 5.9 Code of the Short Name Application
135
ADVANCED PROGRAMMING CONCEPTS
Let us now understand the code in detail line by line:
String FirstName,MiddleName,LastName,ShortName=””;
Declare four variables of type String and initialize them with blanks (to ensure
that it is an empty string).
FirstName=jTextField1.getText().substring(0,1); and
MiddleName=jTextField2.getText().substring(0,1);
First retrieve the values of First Name and Middle Name entered in the first and
second text fields using the getText() method and then extract the first
character of both the First Name and Middle Name using the substring()
method and store them in the variables FirstName and MiddleName
respectively.
LastName=jTextField3.getText();
Retrieve the value of the Last Name entered by the user in the third text field
using getText() method and store it in the variable named LastName.
ShortName=ShortName.concat(LastName); and
ShortName=ShortName.concat(” “); and
ShortName=ShortName.concat(FirstName); and
ShortName=ShortName.concat(“.”); and
ShortName=ShortName.concat(MiddleName); and
ShortName=ShortName.concat(“.”);
Initially the variable ShortName is blank. It is first joined together with
LastName and then with a blank space after which it is joined together with
variable FirstName, dot, variable Middlename and a dot again respectively
using the concat() method. Finally, the content of the ShortName will be the
LastName followed by the initials of the name entered by the user.
jTextField4.setText(ShortName);
The ShortName is then displayed in the fourth text field using the setText()
method.





136
ADVANCED PROGRAMMING CONCEPTS
Let us first design the form as shown in Figure 5.10. First add a new JFrame form and set
its title property to “SMS Testing”. Now, add the following components on the form:
One editable text field to accept the SMS string
Two non-editable text fields – one to display the number of characters entered
by the user and the other to display how many more characters can be entered
(to reach the maximum allowed length)
Three labels – one against each of the text field to appropriately direct the
user.
Change the properties of the components so that the form looks exactly like the one
displayed in Figure 5.10. The next step is to associate code with the text field. Double
click on the text field in the design window to reach the point in the source window where
the code needs to be written. Add the code as given in Figure 5.11.
Figure 5.10 Sample Run of the SMS Testing Application
private void
jTextField1ActionPerformed(java.awt.event.ActionEvent evt)
{ //Display the total number of characters entered and
remaining to be
//entered in a SMS



137
ADVANCED PROGRAMMING CONCEPTS
String SMS=jTextField1.getText();
int L=SMS.length(); // calculate the current length of
the input message
int Balance;
Balance=160-L; // calculate the remaining no. of
characters
jTextField2.setText(Integer.toString(L));
jTextField3.setText(Integer.toString(Balance));
}
Figure 5.11 Code for the SMS Testing Application
Let us now understand the code in detail line by line:
String SMS=jTextField1.getText();
Declare a variable named SMS of type String and initialize it with the value
input by the user in the first text field. The value entered in the text field is
retrieved using method getText().
int L=SMS.length(),Balance;
Declare two variables – Balance and L of integer type. Initialize the variable
named L with the length of the SMS entered by the user. The length is
calculated using the in-built method length() of the String class.
Balance=160-L;
Calculate the balance number of characters by subtracting the length of the
SMS entered from 160 (the maximum number of characters that can be
entered)
jTextField2.setText(Integer.toString(L)); and
jTextField3.setText(Integer.toString(Balance));
Convert the variables L and Balance to type String using the toString() method
and then display these values in the relevant text fields using the setText()
method.




138
ADVANCED PROGRAMMING CONCEPTS
The SMS sample application developed above can further be modified with the help of a
Text Area to give a better view of the SMS. Let us first design the form as shown in Figure
5.12. First add a new JFrame form and set its title property to “SMS Typist”. Now, add the
following components on the form:
One editable text area to accept the SMS message
Two non-editable text fields – one to display the number of characters entered
by the user and the other to display how many more characters can be entered
(to reach the maximum allowed length)
Three labels – one against each of the two text fields and the text area to
appropriately direct the user.
Two buttons – one to reset the form components and the second to exit from the
application
Change the properties of the components so that the form looks exactly like the one
displayed in Figure 5.12. The next step is to associate code with the Text Area and the
buttons. Double click on the text area and the two buttons, one by one, in the design
window to reach the point in the source window where the code needs to be written. Add
the code for the each of the three components as given in Figure 5.13.
Figure 5.12 Sample Run of the SMS Typist Application




139
ADVANCED PROGRAMMING CONCEPTS
private void
jTextArea1CaretUpdate(javax.swing.event.CaretEvent evt)
{
// Display the total number of characters input and
remaining for an SMS
String SMS=jTextArea1.getText();
int L=SMS.length(),Balance;
Balance=160-L;
jTextField2.setText(Integer.toString(L));
jTextField3.setText(Integer.toString(Balance));
}
private void
jButton1ActionPerformed(java.awt.event.ActionEvent evt)
{ // Clear all text fields by initializing them with blank
spaces
jTextArea1.setText(“”);
jTextField2.setText(“”);
jTextField3.setText(“”);
}
private void
jButton2ActionPerformed(java.awt.event.ActionEvent evt)
{ //Exit the application
System.exit(0); //The parameter 0 indicates a normal
termination
}
Figure 5.13 Code for the SMS Typist Application
140
ADVANCED PROGRAMMING CONCEPTS
The code for the text area is exactly same as the one written in the previous example with
just a minor difference. In this case, the SMS is retrieved from the text area instead of the
text field. The rest of the code is exactly the same. The code for the two buttons is also
similar to all previous applications having a RESET and a STOP button.
Observe that the event jTextField1ActionPerformed will display the number
of characters input and left only after the user presses Enter marking the end
of the input. If the user is interested in seeing the status of the number of
words input and number of words that can be accepted on the spot while
inputting the text, then i n s tead of using the event
jTextField1ActionPerformed(java.awt.event.ActionEvent evt), we can use
the jTextField1CaretUpdate(javax.swing.event.CaretEvent evt) as shown
below:
private void
jTextField1CaretUpdate(javax.swing.event.CaretEvent evt)
{
String SMS=jTextField1.getText();
int L=SMS.length(),Balance;
Balance=160-L;
jTextField2.setText(Integer.toString(L));
jTextField3.setText(Integer.toString(Balance));
}
Note: For writing the code for jTextField1CaretUpdate Event, we need to use
the Steps as shown in the following figure:
Extra Reading
141
ADVANCED PROGRAMMING CONCEPTS
Figure 5.14 Steps for writing the code for jTextField1CaretUpdate Event
What will happen if the user enters more number of characters than the permissible
range or enters unnecessary blank spaces before the beginning of the string? The SMS
example can further be modified to solve the above problem. We will now develop an
application which will remove the unwanted leading and trailing blanks and also truncate
the SMS to the permissible range using the trim() and the substring() methods of the
String class. Let us first design the form as shown in Figure 5.15. First add a new JFrame
form and set its title property to “SMS Generator”. Now, add the following components on
the form:
Two editable text areas – one to accept the SMS message and the second to
display the final truncated SMS.
Two non-editable text fields – one to display the number of characters entered
by the user and the other to display how many more characters can be entered
(to reach the maximum allowed length).
Four labels – one against each of the two text areas and the two text fields to
appropriately direct the user.
Two buttons – one to truncate and display the SMS in the text area and the other
to reset the form components.




142
ADVANCED PROGRAMMING CONCEPTS
Figure 5.15 Sample Run of the SMS Generator Application
Change the properties of the components so that the form looks exactly like the one
displayed in Figure 5.15. The next step is to associate code with both the buttons. Double
click on the buttons one by one in the design window to reach the point in the source
window where the code needs to be written. Add the code for each of the buttons as given
in Figure 5.16.
Let us now understand the code in detail line by line:
String SMS,FinalSMS;
Declare two variables named SMS and FinalSMS of type String.
SMS=jTextArea1.getText();
Retrieve the SMS entered by the user in the first text area using the getText()
method and store it in the variable SMS.
if (SMS.length()>160)
{
SMS=SMS.substring(0,159);
}


143
ADVANCED PROGRAMMING CONCEPTS
Check if the length of the SMS entered by the user is greater than 160 (using the
length() method), then extract only first 160 characters (using substring()
method) and store it in the variable SMS.
FinalSMS=SMS.trim();
Remove White Spaces from both sides of the SMS input by the user and store the
resultant SMS in the variable named Final SMS.
FinalSMS=”*”+FinalSMS+”*”;
Add the character “*” on both sides of the message
jTextArea2.setText(FinalSMS);
Display the final sms in the second text area using the setText() method.
private void
jButton1ActionPerformed(java.awt.event.ActionEvent evt)
{ // Truncate the SMS to 160 characters and display it
String SMS,FinalSMS;
SMS=jTextArea1.getText();
if (SMS.length()>160)
{
SMS=SMS.substring(0,159); // Pick up the first 160
characters
}
FinalSMS=SMS.trim(); //Removes White Space from both sides
FinalSMS=”*”+FinalSMS+”*”; //Add a ‘*’ on both sides of
the final SMS
jTextArea2.setText(FinalSMS);
}




144
ADVANCED PROGRAMMING CONCEPTS
private void
jButton2ActionPerformed(java.awt.event.ActionEvent evt)
{ //Clear all the text fields by initializing them with
blank space
jTextArea1.setText(“”);
jTextField2.setText(“”);
jTextField3.setText(“”);
jTextArea2.setText(“”);
}
private void
jTextArea1CaretUpdate(javax.swing.event.CaretEvent evt)
{ // Display the number of characters input and no. of
remaining characters
String SMS=jTextArea1.getText();
int L=SMS.length(),Balance;
Balance=160-L;
jTextField2.setText(Integer.toString(L));
jTextField3.setText(Integer.toString(Balance));
}
Figure 5.16 Steps for writing the code for jTextField1CaretUpdate Event
145
ADVANCED PROGRAMMING CONCEPTS
Summary








EXERCISES
Java supports native classes like Math and String with predefined methods to
make the programming process simpler.
The pow(d1,d2) method of the Math class returns the value d1raised to d2.
The round(d) method of the Math class returns the closest integer/float to d.
The concat(str) method of the String class concatenates the string named str to
the string calling the method.
The length() method of the String class returns the number of characters in the
string.
The toLowerCase() and toUpperCase() methods of the String class return the
string converted to lower case and upper case respectively.
The substring(n1, n2) method of the String Class returns the extracted
characters starting from the position n1 till n2.
The trim() method of the String class returns the string after removing the
leading and the trailing blanks.
1. The ____________ method is used to extract specified number of characters from a
string.
A. subStr() B. subString()
C. takeString() D. extract()
2. Which of the following method(s) does not accept any arguments?
A. pow() B. toLowerCase()
C. round() D. All of the above
3. Which of the following statement is true?
A. The trim() method is used to trim a string by removing spaces from one side
MULTIPLE CHOICE QUESTIONS
146
ADVANCED PROGRAMMING CONCEPTS
B. The trim() method is used to trim a number by removing zeroes
C. The trim() method is used to trim a string by removing spaces from both sides.
D. The trim() method is used to trim a string by removing extra characters.
4. Which of the following is not a valid method of the String class?
A. length() B. concat()
C. trim() D. round()
5. ____________ is a class which contains methods for basic numerical operations like
rounding off the number.
A. Number B. String
C. Math D. Integer
6. What will be the effect of executing the following code:
String F1=”INTER”,F2=”MEDIATE”;
F1=F1.concat(F2);
A. F2 will be concatenated at end of F1 and stored in F1.
B. F1 will be concatenated at end of F2 and stored in F1.
C. F1 will be concatenated at end of F2 and stored in F2.
D. F2 will be concatenated at end of F1 and stored in F2.
7. What will be the contents of L after executing the following code?
String F1=”I#N#T#E#R”,F2; //# represents a space
F2=F1.trim();
int L=F2.length();
A. 5 B. 9
C. 10 D. 6
8. Which of the following is not a primitive data type in Java?
A. float B. int
C. string D. void
147
ADVANCED PROGRAMMING CONCEPTS
ANSWER THE FOLLOWING QUESTIONS
1. What is a class?
2. Name any four native classes of Java and briefly explain the use of each.
3. Give two appropriate advantages of using in-built methods over creating user
defined methods.
4. Explain the general syntax of using any method of the String class. Is it in anyway
different from using a method of the Math class?
5. What will be the contents of F1 and F2 after the following code is executed?
String F1=”Hello”,F2=”Friend”;
F1=F1.concat(F2);
6. Tanyaman is creating a simple application in java called “Password Checker” in which
she needs to convert the characters input by the user in a particular case. Name two
methods of the String class that she can use for this purpose.
7. Aryamani is creating a simple application in java called “Name Concatenator” in
which he needs to concatenate the first name, middle name and last name input by
the user in separate text fields. Name a method and an equivalent operator for this
purpose.
8. Study the following code and answer the questions that follow:
double Number,RoundedNumber;
Number=Double.parseDouble(jTextField1.getText());
RoundedNumber=Math.round(Number*1000)/1000.0;
jTextField2.setText(Double.toString(RoundedNumber));
a) How many variables have been declared in the above code? Identify and name
them.
b) How many objects have been declared in the above code?
c) Name any one native class of Java used in the above code.
d) Identify and name a method of this native class.
148
ADVANCED PROGRAMMING CONCEPTS
e) Name the method used to convert one type of data to another and also mention
the data type before and after conversion.
1. Create an application to accept two strings – First Name and Last name from the user
and display the message Welcome with the complete name of the user.
2. Create an application to accept the radius of a circle, calculate the area and
circumference and display the results in a message box after rounding off the area
and circumference to an integer number.
3. Modify application to make sure that the user has not input the complete name in
the first name text field.
4. Modify the Case Changer application developed in the lesson to display the input
text in Title case using the substring(), toLowerCase() and toUpperCase() methods.
(Team size recommended: 3 students each team)
1. Divide the class into groups of 4 students each and tell them to create a GUI
application that allows a user to change his password according to the following
guidelines:
a. The form should accept the name and password from the user
b. Only if the password matches with the pre-input password, the user should be
allowed to proceed. (Hint – need to check the length and the contents and also
convert the string to a particular case)
c. Hide the initial text fields and now create form elements to accept input of
first name, middle name and last name along with the age.
d. Ensure that the age input is an integer and the first name, middle name and the
last name are not more than 12 characters long.
2. Divide the students into groups of 6 and then give each group an algorithm which is
predesigned by the teacher, and tell them to execute it. This algorithm should draw
a figure with the children; the first team to find the figure and name it wins.
† LAB EXERCISES
TEAM BASED TIME BOUND EXERCISES
† The students should be encouraged to design appropriate forms for the applications themselves.
149
ADVANCED PROGRAMMING CONCEPTS
For example :
child[1].AtLeftOf(child[2])
child[0].InFrontOf(child[2])
child[2].InFrontOf(child[4])
child[3].AtRightOf(child[2])
child[4]. InFrontOf(child[5])
The algorithm given above is to form the shape of an arrow as depicted in the
following figure:
Child 4
Child 5
Child 0
Child 1 Child 3
150
DATABASE CONNECTIVITY
Learning Objectives





6 Puzzle
Introduction
After studying this lesson the students will be able to:
State the need of saving data in the database
Connect a GUI interface with data stored in database.
Use various methods to retrieve data from a database.
Write a complete GUI application with database connectivity
State the advantages of developing applications in local languages
In the earlier lessons, you have learnt how to develop a GUI Interface using
Netbeans and creating & manipulating data in a table of a database as two
independent concepts. This lesson will help you to combine both these concepts
together and help you to develop complete applications in which the GUI
Interface will act as Front-End or Client Side application and Database will act as
Back-End or Server-Side application.
A person wanted to withdraw X rupees and Y paise from the bank. But the cashier made a
mistake and gave him Y rupees and X paise. Neither the person nor the cashier noticed
that. After spending 20 paise, the person counts the money. And to his surprise, he has
double the amount he wanted to withdraw. Find X and Y.
(1 Rupee=100 paise)
Imagine a swanky air-conditioned car showroom in prime location of the city with all
modern car accessories available in an outlet within the showroom. The showroom has a
PT
A
E
H
R
C
6
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wonderful ambience, employs skilled salesperson with excellent communication skills to
convince prospective buyers. They have a tie-up with various banks and financial
agencies to provide lucrative payment plans to lure customers. What do you think he will
sell? Do you think this showroom will be able to cover cost without selling cars? Do you
think the skilled salesperson with excellent communication skills will be able to
manufacture cars?
On the other hand there is a factory, as usual in a remote location, with abundant raw
material, latest machinery, skilled workforce that is technically sound with latest
automobile expertise. The factory keeps manufacturing cars but does not have any
dealers. Factories are generally set up in remote industrial towns so do you think a
remote area in Gujrat will be able to sell cars directly from their factory? Do you think the
factory will be able to cover their costs incurred on raw materials without delivering cars?
Do you think a skilled workforce can convince people to buy cars?
As you know that the programmers develop applications for solving real life problems to
simplify life of others. That is the reason, they try to develop applications, which require
minimum inputs from the user and provide meaningful information in the form of output
through their applications. The programmer develops these applications keeping in mind
that the user will have a very basic understanding of handling mouse, keyboard and
desktop applications. In the earlier lessons of GUI programs, you must have got a good
idea of developing simple GUI Applications, in which user was typing in or clicking on
certain inputs to produce meaningful results (output). If you see all these applications
carefully, you will realize that none of them are capable of retaining the inputs or outputs
for future reference or uses. So, typing in any number of inputs in the application carries
a life span of one execution only and when the application is executed second time, it
requires a new set of inputs from the user. Do you realize why it is like this? It is because;
the data entered by you in a front end application was getting stored in temporary
memory (RAM) and not getting saved on a hard disk (or any other secondary storage
device).
GUI Application (The Front-End)
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DATABASE CONNECTIVITY
Database (The Back-End)



The database helps you to save data permanently in secondary storage devices and keeps
data ready for future reference, modification and addition. In the earlier lessons about
database concepts, you have learnt about how to create a table, modify content of a
table, add new content in the table, delete content from a table and retrieve content
from a table in various forms. But you must have seen that to perform these activities,
you were required to learn SQL commands like CREATE, UPDATE, INSERT, DELETE, SELECT
and so on and each of these commands had their own syntax structures. Let us review
this with the help of the Employee table shown below:
1001 Jasmine Taneja 45000
1009 Ravi Mathwad 34000
1015 Desai Ramakrishnan 58000
1004 Jigyasa Burman 49000
The SQL commands
to add a new row in the table:
INSERT INTO Employee VALUES (1013, “Punya Sarthi”, 51000);
to retrieve the entire content from the table:
SELECT * FROM Employee;
Table: Employee
Empno Name Salary
to increase salary by 10% for the employee whose Empno is 1009:
UPDATE Employee SET Salary=Salary*1.1 WHERE Empno=1009;
Obviously, you do not expect the user to learn all these commands to perform these
activities. User always likes to access the information using the computer with some
clicks of mouse or by typing in little textual input as per instructions provided preferably
in his/her local language. So, there is a need to provide him/her with an interface to
access or modify the information available in the database.
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Database Connectivity (Front-End + Back-End)


After looking at the role of the Front-End and the Back-End, it is clear that the Car
showroom in our introduction is actually our front end and the factory is nothing but the
back end which supplies cars to the showroom. The showroom owner will be able to cover
the costs incurred on running and maintaining the showroom only if the cars are delivered
to the showroom by the factory. Similarly, the factory needs to send the cars to the
showroom set up in an urban area for selling. Setting up an effective link between the two
ends to facilitate the transfer of cars is the only solution of all the stated problems.
After going through the above paragraphs, you can understand that there is a
requirement of creating an interface (the form), which a user may use for accessing
information and also there is a requirement of keeping the information saved in the
database (table) in an organized manner for future references and uses. So, we need to
combine both these concepts together to develop a complete application for various
domain specific problems. Now after learning about the front end and the back end, the
next step is to learn how to set up a database connection that allows the front end to
communicate with the back end. The two components essential to establish this
connectivity are enumerated below and demonstrated in Figure 6.1:
The JDBC API – software used to provide RDBMS access and execute SQL
statements within java code.
The JDBC Driver for MySQL – software component enabling a java application to
interact with a MySQL database.
Figure 6.1 Communicating With a Database Using JDBC API and Driver
Database: School
Table: Student
Arun 12
Ajay 11
Name Class
Table: Fee
Arun 6500
Ajay 4500
Name Fee
Application:Form
Name
Class
OK Cancel
jdbc Driver
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DATABASE CONNECTIVITY
Know more
An application programming interface (API) is an interface implemented by a
software program which enables it to interact with other software. It facilitates
interaction between different software programs similar to the way the user
interface facilitates interaction between humans and computers.
The first step for establishing data connectivity is to add the MySQL JDBC Driver Library
for use by your project. Remember, that this process has to be repeated every time you
start a new project but not for new forms or applications added to an existing project.
To add the MySQL JDBC Driver Library follow the given steps.
Step 1: Right click on the Project name and select the Properties option as shown in
Figure 6.2.
Step 2: In the Properties dialog box,
i. choose the Libraries option from the Categories pane
ii. click on the Add Library button as shown in Figure 6.3.
iii. From the Add Library dialog box choose the MySQL JDBC Driver
iv. Click on the Create button as shown in Figure 6.3.
Adding [MySQL JDBC Driver] Library in NetBeans
Figure 6.2 Opening Project Properties Dialog Box
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DATABASE CONNECTIVITY
Figure 6.3 Adding the MySQL JDBC Driver From Available Libraries
The JDBC (Java Database Connectivity) API is a software for executing SQL
statements. It provides RDBMS access by allowing you to embed SQL inside Java
code. We can create a table, insert values into it, query the table, retrieve
results, and update the table with the help of JDBC.
The driver is now added to the compile time libraries and this can be verified by clicking
on the Compile Time Libraries tab in the Project Properties dialog box as shown in Figure
6.4. Click on OK to close the Project Properties dialog box.
Know more
i
iii
ii
iv
Figure 6.4 Compile-Time Libraries
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DATABASE CONNECTIVITY
Basic Libraries Required in the Application for Data Connectivity



Apart from the MySQL JDBC driver, we also need to import some basic class libraries which
are essential for setting up the connection with the database and retrieve data from the
database – namely DriverManager Class, Connection Class and Statement Class. These
class libraries can be added using the following commands in our application code:
import java.sql.DriverManager;
import com.mysql.jdbc.Connection;
import com.mysql.jdbc.Statement;
Let us quickly understand the basic purpose for each of these class libraries:
The JDBC DriverManager class defines objects which can connect Java
applications to a JDBC driver. DriverManager is considered the backbone of
JDBC architecture. DriverManager class manages the JDBC drivers that are
installed on the system. Its getConnection() method is used to establish a
connection to a database. It uses a username, password, and a jdbc url to
establish a connection to the database and returns a connection object.
A JDBC Connection represents a session/connection with a specific database.
Connection interface defines methods for interacting with the database via
the established connection. An application can have one or more connections
with a single database, or it can have many connections with different
databases.
Once a connection is obtained we can interact with the database. To execute
SQL statements, you need to instantiate (create) a Statement object using the
connection object. A Statement object is used to send and execute SQL
statements to a database.
In case any of these libraries are missing, then the execution results in an error as shown
in Figure 6.5.
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DATABASE CONNECTIVITY
Figure 6.5 Error Window Indicating Missing DriverManager Library
Now that we have learnt the basics about establishing a connection, let us start
developing an application that uses database connectivity. The aim of the first
application that we will develop is to add data into a table.
Using MySQL command prompt, create a Table named “Contact” in the Database CBSE,
with the specified table structure. The relevant command is shown in Figure 6.6.
Figure 6.6 Command for creating the back end Table with a specified structure
Now let us design the form as shown in Figure 6.7. First add a new JFrame form and set its
title property to “Contact List”. Now, add the following components on the form:
Three editable text fields to accept the name, mobile number and email
address from the user.
Three appropriate labels – one against each of the text field to direct the user.
Data Connectivity Application 1: Add Records in a Table Input Through a Form


USE CBSE;
CREATE TABLE Contact (Name VARCHAR(20),Mobile VARCHAR(12),
Email VARCHAR(25));
Name VARCHAR(20)
Mobile VARCHAR(12)
Table
Structure
Command for
creating the Table
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DATABASE CONNECTIVITY
Two buttons – one to add the data supplied by the user in the database and one
to exit from the application.
Change the properties of the components as learnt earlier so that the form looks exactly
like the one displayed in Figure 6.7. The next step is to associate code with both the
buttons. Double click on the buttons one by one in the design window to reach the point in
the source window where the code needs to be written. Add the code for each of the
buttons as given in Figure 6.8.
Figure 6.7 Front-end Form for the Contact List Application
//NetBeans Application 1 – To add new row(s) in the Contact Table
private void
jButton1ActionPerformed(java.awt.event.ActionEvent evt)
{
//Declare variables and store values retrieved from the
front end
String Name=jTextField1.getText();
String Mobile=jTextField2.getText();
String Email=jTextField3.getText();
try
// this block is executed in case of normal execution

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{
Class.forName(“java.sql.DriverManager”);
Connection con = (Connection)
DriverManager.getConnection
(“jdbc:mysql://localhost:3306/cbse”,
“root”, “abcd1234″);
Statement stmt = (Statement) con.createStatement();
String query=”INSERT INTO Contact VALUES
(‘”+Name+”‘,'”+Mobile+”‘,'”+Email+”‘);”;
stmt.executeUpdate(query);
}
catch(Exception e)
//this block is executed in case of an exception
{
//Display an error message in the dialog box for an exception
JOptionPane.showMessageDialog (this, e.getMessage());
}
}
// This part of the code is used to exit from the application
private void
jButton2ActionPerformed(java.awt.event.ActionEvent evt)
{
System.exit(0);
}
Figure 6.8 Code for the Contact List Application
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DATABASE CONNECTIVITY
Know more



To catch an exception in Java, you write a try block with one or more catch
clauses. Each catch clause specifies one exception type that it is prepared to
handle. The try block delimits a bit of code that is under the watchful eye of the
associated catchers. If the bit of code delimited by the try block throws an
exception, the associated catch clauses will be examined by the Java virtual
machine. If the virtual machine finds a catch clause that is prepared to handle the
thrown exception, the program continues execution starting with the first
statement of that catch clause. For example, in the above code if any error occurs
while establishing a connection or executing the SQL query then the error message
will be displayed in a message box due to the catch block immediately following
the try block.
Let us now understand the code in detail line by line:
String Name=jTextField1.getText(); and
String Mobile=jTextField2.getText(); and
String Email=jTextField3.getText();
Declare three variables named Name, Mobile and Email of type String and
initialize them with the values input by the user in the text fields. The values
are retrieved from the text fields using the getText() method.
Class.forName(“java.sql.DriverManager”);
In this step of the jdbc connection process, we load the driver class by calling
Class.forName() method with the Driver class name as an argument. Once
loaded, the Driver class creates an instance of itself. A client can then connect
to the Database Server through JDBC Driver.
Connection con = (Connection)
DriverManager.getConnection
(“jdbc:mysql://localhost:3306/cbse”, “root”, “abcd1234″);
The getConnection() method of the DriverManager class is used to establish a
connection to the cbse database. The method uses a username, password, and
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DATABASE CONNECTIVITY
a jdbc url to establish a connection to the database and returns a connection
object named con.
In the above command:
jdbc:mysql – is the Database Driver Connection
3306 – is the Default Port no on which MySQL runs
cbse – is the Database Name
root – is the User Name
abcd1234 – is the Password
Statement stmt = (Statement) con.createStatement();
Instantiate a Statement object called stmt from the connection object (named
con created in the previous statement) by using the createStatement()
method. A statement object is used to send and execute SQL statements to a
database.
String query=”INSERT INTO Contact VALUES
(‘”+Name+”‘,'”+Mobile+”‘,'”+Email+”‘);”;
Create a variable called query of type String and initialize it with the SQL
statement to be executed (in this case the INSERT INTO statement).
stmt.executeUpdate(query);
Execute the SQL statement stored in the variable query, using the
executeUpdate() method of the Statement class. This results in adding the
values stored in the three variables (Name, Mobile & Email) in the table
Contact of the cbse database.
catch (Exception e)
{
JOptionPane.showMessageDialog (this, e.getMessage());
}




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DATABASE CONNECTIVITY
In case of an exception, retrieve the error message string using the
getMessage() method and display it in a dialog box using the
showMessageDialog() method.
Note that the forName() method is used to load the class specified as its argument
at runtime.
Figure 6.9 shows a sample run of the above application.
Figure 6.9 Sample Run of the Contact List Application Showing Error Message
The above application can be modified to handle basic data validations as shown in Figure
6.10.
Note that Data validation is the process of ensuring that a program operates on
clean, correct and useful data. It uses routines, often called “validation rules” or
“check routines”, that check for correctness, meaningfulness, and security of data
that are input to the system. For example, telephone numbers should include the
digits and possibly the characters + & -. A more sophisticated data validation
routine may check to see the user has entered a valid country code, i.e., that the
number of digits entered match the convention for the country or area specified.

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DATABASE CONNECTIVITY
//Netbeans Application 1 (with Data Validation)
//- To add new row(s) in the Contact Table
private void
jButton1ActionPerformed(java.awt.event.ActionEvent evt)
{ String Name=jTextField1.getText();
String Mobile=jTextField2.getText();
String Email=jTextField3.getText();
/* Check if any of the variable is empty and accordingly
display
an appropriate error message */
if (Name.isEmpty())
JOptionPane.showMessageDialog(this,”Name not Entered”);
else if (Mobile.isEmpty())
JOptionPane.showMessageDialog(this,”Mobile not Entered”);
else if (Email.isEmpty())
JOptionPane.showMessageDialog(this,”Email not Entered”);
else
{ try
{
Class.forName(“java.sql.DriverManager”);
Connection con = (Connection)
DriverManager.getConnection
(“jdbc:mysql://localhost:3306/cbse”, “root”,
“abcd1234″);
Statement stmt = (Statement) con.createStatement();
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DATABASE CONNECTIVITY
String query=”INSERT INTO Contact VALUES
(‘”+Name+”‘,'”+Mobile+”‘,'”+Email+”‘);”;
stmt.executeUpdate(query);
jTextField1.setText(“”);
jTextField2.setText(“”);
jTextField3.setText(“”);
}
catch (Exception e)
{
JOptionPane.showMessageDialog (this, e.getMessage());
}
}
Figure 6.10 Code for the Contact List Application with Data Validations
Let us now understand the purpose of the additional commands added to the above code:
if (Name.isEmpty())
JOptionPane.showMessageDialog(this,”Name not Entered”);
else if (Mobile.isEmpty())
JOptionPane.showMessageDialog(this,”Mobile not Entered”);
else if (Email.isEmpty())
JOptionPane.showMessageDialog(this,”Email not Entered”);
else { …..}
Check if the value of any of the three variables (Name, Mobile, Email) is empty
using the isEmpty() method with the help of the if..else conditional statement.
In case any of the values is empty then display a error message in a dialog box
using the showMessageDialog() method.

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DATABASE CONNECTIVITY
catch (Exception e)
{ JOptionPane.showMessageDialog (this, e.getMessage()); }
In case of an exception, retrieve the error message string using the
getMessage() method and display it in a dialog box using the
showMessageDialog() method.
The code for the exit button is the same as all our previous applications.
Note that an exception is an event, which occurs during the execution of a
program, that disrupts the normal flow of the program’s instructions.
After executing the Contact List Application, if you need to verify whether the row has
been added to the table or not, then you need not go back to the MySQL prompt.
Netbeans allows one to directly run SQL commands from the GUI interface.
Therefore, the content of the table can directly be tested by running SQL in Netbeans. To
execute an SQL command in Netbeans perform the following steps:
Step 1: In the Services tab, right click on the Databases and select the New Connection
option from the drop down menu.
Step 2: The New Database Connection dialog window opens up as shown in the Figure
6.11. Provide the values as shown in the figure and click OK. Clicking on OK in
the above dialog window adds the connection to the existing list as shown in
the Figure 6.12. Note that this step is required to be done only once – the first
time when creating a connection.

Running SQL Commands in Netbeans
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DATABASE CONNECTIVITY
Figure 6.11 Setting Up a New Database Connection
Step 3: Right click on the newly added Connection and select the Connect option from
the drop down menu. This step is to be repeated every time you start Netbeans.
In the Connect dialog box that opens up, enter the user name and password and
select the Remember Password checkbox (Selecting this checkbox ensures that
this step is not to be repeated every time you start Netbeans) as shown in
Figure 6.12.
Newly added
connection
Figure 6.12 Connecting to the Appropriate Database
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DATABASE CONNECTIVITY
After establishing the connection, right click on the connection driver and select the
Execute Command option from the drop down menu. The screen as shown in Figure 6.13 is
displayed. Now, type in any SQL to be executed on the database and execute the
command. The result is displayed in the bottom half of the window as shown in Figure
6.13.
Figure 6.13 Executing SQL Command Directly in Netbeans
The next application that we will develop can be used to display data retrieved from a
database in a form, one record at a time. Add a few records to the table Contact created
above. Now design the form as shown in Figure 6.14. First add a new JFrame form and set
its title property to “Search From Contacts”. Now, add the following components on the
form:
One editable text field to accept the mobile number from the user.
Two non-editable text fields to display the details – Name and E-mail of the
contact being searched.
Data Connectivity Application 2: To Display Records Retrieved from a Database (Back
End) in a Form (Front End) one by one


SQL Command
Rows
retrieved from
the database
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DATABASE CONNECTIVITY
Three appropriate labels – one against each of the text field to direct the user.
Two buttons – one to search for the details on the basis of a mobile number
supplied by the user and one to exit from the application.
Figure 6.14 Sample Run of Search From Contacts Application
Change the properties of the components as learnt earlier so that the form looks exactly
like the one displayed in Figure 6.14. The next step is to associate code with both the
buttons. Double click on the buttons one by one in the design window to reach the point in
the source window where the code needs to be written. Add the code for each of the
buttons as given in Figure 6.15.
/*Netbeans Application 2 (Basic Part) – To search for a
matching row and display corresponding information from the
table Contact */
private void
jButton1ActionPerformed(java.awt.event.ActionEvent evt)
{
// Search the table to find a record matching
// the input Mobile no.
String Mobile=jTextField1.getText();
if (Mobile.isEmpty())
//Execute this part if text field is blank


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DATABASE CONNECTIVITY
{
jTextField2.setText(“”);
jTextField3.setText(“”);
JOptionPane.showMessageDialog
(this,”Enter the Mobile No”);
}
// This part is executed if a Mobile No is
// input in the text field
else
{
try
{
Class.forName(“java.sql.DriverManager”);
Connection con = (Connection)
DriverManager.getConnection
(“jdbc:mysql://localhost:3306/cbse”,
“root”, “abcd1234″);
Statement stmt = (Statement) con.createStatement();
String query=”SELECT NAME,EMAIL FROM CONTACT
WHERE MOBILE='”+Mobile+”‘;”;
ResultSet rs=stmt.executeQuery(query);
if (rs.next())
{
String Name = rs.getString(“Name”);
//Retrieve the name
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DATABASE CONNECTIVITY
String Email = rs.getString(“Email”);
//Retrieve the email
jTextField2.setText(Name);
Figure 6.15 Code for the Search From Contacts Application
jTextField3.setText(Email);
}
// This part is executed if no matching record is found
else
JOptionPane.showMessageDialog
(this,”Sorry!No such Mobile No”);
}
catch (Exception e)
{
JOptionPane.showMessageDialog(this, e.getMessage());
}
}
}
private void jButton2ActionPerformed
(java.awt.event.ActionEvent evt)
{
System.exit(0);
}
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DATABASE CONNECTIVITY
Let us now understand the code in detail line by line:
String Mobile=jTextField1.getText();
Declare a variable called mobile and initialize it with the value input by the
user in the first text field which has been retrieved using the getText() method.
if (Mobile.isEmpty())
{
jTextField2.setText(“”);
jTextField3.setText(“”);
JOptionPane.showMessageDialog(this,”Enter the Mobile No”);
}
Check if the mobile variable is empty i.e. in case the user has not input any
mobile number then reinitialize both the text fields with blank spaces using the
setText() method and show an error message using the showMessageDialog()
method.
else
{
try
{
Class.forName(“java.sql.DriverManager”);
Connection con = (Connection)
DriverManager.getConnection
(“jdbc:mysql://localhost:3306/cbse”,root”,
“abcd1234″);
Statement stmt = (Statement) con.createStatement();
String query=”SELECT NAME,EMAIL FROM CONTACT
WHERE MOBILE='”+Mobile+”‘;”;


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DATABASE CONNECTIVITY
If the user has entered a valid mobile number then perform all the steps for
setting up a connection and initializing a query as learnt in the first database
application.





ResultSet rs=stmt.executeQuery(query);
Instantiate an object named rs of the ResultSet class and initialize it with the
records returned by executing the SQL statement stored in the query variable.
The executeQuery() method is used when we simply want to retrieve data from
a table without modifying the contents of the table.
if (rs.next())
Check if there is a matching record in the result set using the if construct. The
next() method of the result set is used to move to the next record of the
database.
String Name = rs.getString(“Name”);
String Email = rs.getString(“Email”);
jTextField2.setText(Name);
jTextField3.setText(Email);
Create two variables named Name and Email and initialize them with the
values retrieved from the table using the getString() method. Next display
these values retrieved from the table in the relevant text fields using the
setText() method.
else
{ JOptionPane.showMessageDialog
(this,”Sorry!No such Mobile No”); }
If there is no matching record found in the table then display an error message
using the showMessageDialog() method.
catch (Exception e)
{
JOptionPane.showMessageDialog(this, e.getMessage());
}
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DATABASE CONNECTIVITY
Figure 6.17 Error Message Indicating Missing ResultSet Class Library
Observe the sample run of our next application as shown in Figure 6.18 carefully. Can you
observe the difference in this application as compared to our previous one?
• In case of an exception, retrieve the error message string using the
getMessage() method and display it in a dialog box using the
showMessageDialog() method.
A sample run of the validation check applied in the above application is shown in Figure
6.16
Figure 6.16 Validation Message in Search From Contacts Application
Just like we need to add the DriverManager, Connection and Statement class libraries,
similarly we need to import the ResultSet class library when we are retrieving data from a
database. In case the above mentioned library is not imported then the error window is
displayed as shown in Figure 6.17.
Data Connectivity Application 3: To Display the Details Stored in the Back-end Based
on the Name Input by the User in a Form.
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DATABASE CONNECTIVITY
In the previous application, we are searching on mobile number which will be unique i.e.
we will always have a single matching record. What will happen if we perform a search on
Name? In this case there is a possibility that we may have more than one matching record.
So the major difference between the two applications is that in the new application we
will aim at performing a search in which multiple records may be returned.
Figure 6.18 Sample Run of the Search For Contacts (For Given Name)
The form design and most of the coding is similar with minor differences. Observe the
code given in Figure 6.19 carefully and try to point out the differences.
private void
jButton1ActionPerformed(java.awt.event.ActionEvent evt)
{
String name=jTextField1.getText();
if (name.isEmpty())
JOptionPane.showMessageDialog(this,”Name not Entered”);
else
{
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DATABASE CONNECTIVITY
try
{
Class.forName(“java.sql.DriverManager”);
Connection con = (Connection)
DriverManager.getConnection
(“dbc:mysql://localhost:3306/cbse”, “root”,
“abcd1234″);
Statement stmt = (Statement) con.createStatement();
String query=”SELECT Mobile,Email FROM Contact
WHERE Name='”+name+”‘;”;
ResultSet rs=stmt.executeQuery(query);
int Found=0;
while(rs.next())
// Till there are records in the result set
{
String mobile = rs.getString(“Mobile”);
String email = rs.getString(“Email”);
jTextField2.setText(mobile);
jTextField3.setText(email);
JOptionPane.showMessageDialog
(null,”Click OK to continue!!!”);
Found++;
//Increment the variable to indicate a matching
//record has been found
}
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DATABASE CONNECTIVITY
if (Found==0)
Figure 6.19 Code for the Search for Contacts (For Given Name) Application
Let us now discuss the changes (additional commands) made to the previous code one by
one:
i) The first change is declaration of a new integer variable named Found. This
variable is initialized to 0 and is used to keep a track of how many matching
records have been found.
ii) The second change is that we have used while loop to traverse through all the
records in the table to find all possible matching records.
iii) The third change is the statement used to increment the variable found each
time a matching record is encountered.
In all the previous applications we have aimed at displaying only one record at a time in a
form. What if we want to see all the records in one go? The next application is aimed at
solving this problem. The aim of this application is to display all the records in a tabular
form.
JOptionPane.showMessageDialog
(this,”Sorry! No such Name in Contact List”);
}
catch (Exception e)
{
JOptionPane.showMessageDialog(this, e.getMessage());
}
}
}
Data Connectivity Application 4: To Display Records Retrieved From the Back-end in
the Table Component
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DATABASE CONNECTIVITY
First, create a new table named Official with the same structure as that of table Contact.
Add few records in this table.
Now let us design the form. First add a new JFrame form and set its title property to
“Contact List”. Now, add the following components on the form:
One table to display the records retrieved from the table.
Two radio buttons to select whether the records of the Contact table are
displayed or the records of the Official table are displayed.
Two appropriate labels – one against each of the radio button to direct the user.
Three buttons – one to refresh data displayed in the table, one to reset the
table and one to exit from the application.
Change the properties of the radio buttons, labels and button components as learnt
earlier so that the form looks exactly like the one displayed in Figure 6.20. Before
associating the code with the buttons, we need to customize the table component.
Figure 6.20 Form Design of the Modified Contact List Application
Right click on the table component and select Table Contents option to open the
Customizer Dialog window. In this window choose the Columns tab and customize the
column names by changing the Title property of each column as shown in Figure 6.21.




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DATABASE CONNECTIVITY
Next choose the Rows tab and delete all the four default rows. These rows have to be
deleted otherwise they appear as blank rows in the final output and the retrieved data is
displayed from fifth row onwards.
Once the form has been totally customized, the next step is to associate code with all the
three buttons. Double click on the buttons one by one in the design window to reach the
point in the source window where the code needs to be written. Add the code for each of
the buttons as given in Figure 6.22.
Figure 6.21 Customizing Columns and Rows of the Table Component of the Form
Before proceeding to writing the code, let us understand the purpose of the two buttons –
Refresh Data and Reset Table. The purpose of the Refresh Data button is to display the
data from the selected table without clearing the previous data. This means that the new
data will be displayed in continuation of the previous displayed data. Whereas, if we
press the Reset Table button, then it deletes all previous rows of the table component of
the form.
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DATABASE CONNECTIVITY
private void
jButton1ActionPerformed(java.awt.event.ActionEvent evt)
{
DefaultTableModel model = (DefaultTableModel)
jTable1.getModel();
try
{
Class.forName(“java.sql.DriverManager”);
Connection con = (Connection)
DriverManager.getConnection
(“jdbc:mysql://localhost:3306/cbse”,
“root”, “abcd1234″);
Statement stmt = (Statement) con.createStatement();
String Tname;
if (jRadioButton1.isSelected())
Tname=”Contact”;
else
Tname=”Official”;
/* The query is executed on different tables depending
upon the Purpose */
String query=”SELECT * FROM “+Tname+”;”;
ResultSet rs = stmt.executeQuery(query);
while(rs.next())
{
String Name = rs.getString(“Name”);
String Mobile = rs.getString(“Mobile”);
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DATABASE CONNECTIVITY
String Email = rs.getString(“Email”);
model.addRow (new Object[] {Name, Mobile,Email});
}
}
catch (Exception e)
{
JOptionPane.showMessageDialog (this, e.getMessage());
}
}
private void
jButton2ActionPerformed(java.awt.event.ActionEvent evt)
{
DefaultTableModel model = (DefaultTableModel)
jTable1.getModel(); int rows=model.getRowCount();
if (rows>0)
{
for (int i=0; i<rows; i++)
model.removeRow(0); // To remove all rows from
current model
}
}
private void
jButton3ActionPerformed(java.awt.event.ActionEvent evt)
{
System.exit(0);
}
Figure 6.22 Code for the Modified Contact List Application
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DATABASE CONNECTIVITY
Let us now understand the code in detail line by line:
DefaultTableModel model = (DefaultTableModel)
jTable1.getModel();
To retrieve the Model of the newly created table and type cast it to the Default
Model.
Class.forName(“java.sql.DriverManager”);
Connection con = (Connection)
DriverManager.getConnection(“jdbc:mysql://localhost:3306/cbse”,
“root”, “abcd1234″);
Statement stmt = (Statement) con.createStatement();
Instantiate a Connection and a Statement object as before
String Tname;
Declare a variable named Tname of type String. This variable will be sued to
store the name of the table from which the data has to be retrieved.
if (jRadioButton1.isSelected())
Tname=”Contact”;
else
Tname=”Official”;
Check which radio button has been selected and accordingly initialize the
variable Tname.
String query=”SELECT * FROM “+Tname+”;”;
Create a variable called query of type String and initialize it with the SQL
statement to retrieve all records from the specified table. The value of the
specified table is stored in the variable Tname and so this variable is
concatenated with the normal SQL statement.
ResultSet rs = stmt.executeQuery(query);
Execute the SQL query using the executeQuery() method. Instantiate a variable
named rs of class ResultSet to store the records returned by the SQL query.






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DATABASE CONNECTIVITY
while(rs.next())
{
String Name = rs.getString(“Name”);
String Mobile = rs.getString(“Mobile”);
String Email = rs.getString(“Email”);
model.addRow (new Object[] {Name, Mobile,Email});
}
Till there are records in the database, keep retrieving the values of Name,
Mobile and Email from the table one by one using the getString() method and
store them in the three String variables using the assignment operator.
After storing the values in the variables, display these values in the table
component on the form using the addRow() method.
int rows=model.getRowCount();
Declare a variable named rows of type integer and initialize it with the total
number of rows in the table component of the form using the getRowCount()
method.
if (rows>0)
{
for (int i=0; i<rows; i++)
model.removeRow(0);
}
If the number of rows is greater than zero, then use a for loop to reset the table
component i.e. delete all the rows using the removeRow() method. Note that
the parameter passed to the removeRow() method is always zero as we are
always deleting the topmost row and this process is repeated rows number of
times to ensure that all the rows are deleted.




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DATABASE CONNECTIVITY
Data Connectivity Application 5: To Add Records in a Table Accepted Through a Form
with Hindi Interface
Now that we are clear about data connectivity, let us learn a new feature – to add
multilingual support facility to our Netbeans form and database and then display records
in our native language as shown in Figure 6.23.
Figure 6.23 Form Design of the Contact List Application with a Hindi Interface
First create a database named CBSEHINDI using the following command:
CREATE DATABASE CBSEHINDI DEFAULT CHARACTER SET UTF8;
Note that the DEFAULT CHARACTER SET UTF8 has been added to the above command to
have Unicode support for entering and processing data in HINDI language. Adding this
command while creating the database ensures that all tables created within this
database support Hindi language processing.
Next create a table named Contact in the CBSEHINDI database using the following
command:
CREATE TABLE Contact (Name VARCHAR(20),Mobile VARCHAR(12),
Email VARCHAR(25));
Now while creating the form as shown above for the Netbeans application, remember to
use unicode supported fonts for jTextFields, jLabels and jButtons (such as Arial Unicode
MS) as shown in Figure 6.24.
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DATABASE CONNECTIVITY
Figure 6.24 Setting the Font Properties for Multilingual Support
The code will be similar as the earlier example shown in Data Connectivity Application 1
(Only change the name of the database to cbsehindi as shown in the following code) and
Connection con = (Connection)
DriverManager.getConnection(“jdbc:mysql://localhost:3306/cbsehindi”,”root”,
“abcd1234”);
A sample run of the Hindi interface application is shown in Figure 6.25.
Figure 6.25 Sample Run of the Contact List Application with Hindi Interface
All the records in the cbsehindi database are stored in Hindi. Therefore, if we execute an
SQL command to display all the records of the database then the records will be displayed
in Hindi as shown in Figure 6.26.
Clicking on this
button will
terminate the
application
Clicking on this
button will add
the given
details in the
database
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DATABASE CONNECTIVITY
Figure 6.26 Running Simple SQL Statement in Netbeans for Data Display in Hindi
Cloud Computing
Cloud computing is a technology used to access services offered on the Internet
cloud. Everything an Informatics System has to offer is provided as a service, so
users can access these services available on the “Internet Cloud” without having
any previous know-how. The cloud is just one example of a virtualized computing
platform, and the next generation of developer tools must enable developers to
build software that deploys and performs well in cloud and other virtual
environments.
Future Trends
Summary


A GUI (The Front-End) helps the user to design forms to accept data and provide
instructions for retrieving information from the backend.
A database (The Back-End) helps in storing data in organized manner for future
reference and use
Records
displayed
in Hindi
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DATABASE CONNECTIVITY
A link needs to be established between the front end form and the back end
table using jdbc driver (or an equivalent) to facilitate communication between
the two.
A complete application requires a combination of all three concepts i.e. it
requires a user friendly interface, an efficient connection link and a database
The JDBC DriverManager class defines objects which can connect Java
applications to a JDBC driver.
The JDBC Connection interface defines methods for interacting with the
database via the established connection.
To execute SQL statements, you need to instantiate (create) a Statement
object using the connection object.
The getConnection() method of the DriverManager class is used to establish a
connection to the database.
The getMessage() method is used to retrieve the error message string.
The executeUpdate() method of the Statement class is used to update the
database with the values given as an argument.
The executeQuery() method is used when we simply want to retrieve data from
a table without modifying the contents of the table.
The next() method of the result set is used to move to the next record of the
database.
The getModel() method is used to retrieve the model of a table.
The getRowCount() method is used to retrieve the total number of rows in a
table.
The removeRow() method is used to delete a row from a table.
It is possible to add Multilingual support in MySQL database by setting the
appropriate character set while creating the database.














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DATABASE CONNECTIVITY
EXERCISES
MULTIPLE CHOICE QUESTIONS
1. We may use ____________ to develop the Front-End of an application.
A. GUI B. Database
C. Table D. None of the above
2. The ______________ method is used when we simply want to retrieve data from a
table without modifying the contents of the table
A. execute() B. queryexecute()
C. query() D. executeQuery()
3. Which of the following class libraries are essentially required for setting up a
connection with the database and retrieve data?
A. DriverManager B. Connection
C. Statement D. All of the above
4. The _____________ is required to establish connectivity between the Java code and
the MySQL database.
E. JDBC API F. JDBC Driver
G. Both A and B
5. To execute SQL statements, you need to instantiate a _____________ object using
the ______________ object.
A. Connection , Statement B. Statement, Connection
C. JDBC Driver, Statement D. JDBC DriverManager, Statement
6. Which of the following statements are false?
A. The getConnection() method is used to establish a connection.
B. An application can have more than one connection with a database.
C. An application cannot have more than one connection with a database.
D. An application can have many connections with different databases.
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DATABASE CONNECTIVITY
7. The _______________ method is used to instantiate a statement object using the
connection object
A. getConnection() B. getStatement()
C. createConnection() D. createStatement()
8. The ____________ method is used to move to the next row of the result set.
A. next() B. findNext()
C. last() D. forward()
1. What is a GUI?
2. Explain the terms ResultSet with respect to a database.
3. Explain the usage of the following methods:
a) next()
b) removeRow()
4. Give two appropriate reasons of connecting GUI form with a Database.
5. What is JDBC? What is the importance of JDBC in establishing database connectivity.
6. Name the 3 essential class libraries that we need to import for setting up the
connection with the database and retrieve data from the database.
7. Explain the importance of:
a) JDBC b) forName() method
c) getModel() method
8. Consider the following code and answer the questions that follow:
String query=”SELECT NAME,EMAIL FROM CONTACT”
ResultSet rs=stmt.executeQuery(query); //Statement 1
if (rs.next()) //Statement 2
{
ANSWER THE FOLLOWING QUESTIONS
189
DATABASE CONNECTIVITY
String Name = rs.getString(“Name”);
String Email = rs.getString(“Email”);
jTextField2.setText(Name);
jTextField3.setText(Email);
}
a) Name the table from where the data is being retrieved
b) How many objects of the native String class have been declared in the code?
Name the objects.
c) Identify the object name, class name and method name used in the statement
labeled as Statement 1.
d) Explain the function of the statement labeled as Statement 2.
1. Modify the SMS application developed in Chapter 5 to store the messages in a table
along with the number of characters in a message.
2. Modify the password application developed in Chapter 5 to store the name and
password of users in a table. The application should also update the password
whenever the user modifies his password and should keep a count on how many
times the password is being updated.
3. Design a GUI Interface for executing SQL queries for the above developed Password
Application to accomplishing the following tasks:
A. Retrieve a list of all the names and display it in a table form.
B. Retrieve a list of names where name begins with a specific character input by
the user and display it in a table form.
C. Display all records sorted on the basis of the names.
4. Modify the password application developed above to handle processing in Hindi
language.
† LAB EXERCISES
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DATABASE CONNECTIVITY
TEAM BASED TIME BOUND EXERCISES
(Team size recommended: 3 students each team)
1. Divide the class in groups of four and tell each group to develop a phone book
application to store and retrieve information about their friends on the basis of
name, phone number or birthday. The information stored may include name, phone
number, address, birthday, category etc.
2. Each group should next write SQL queries (to be executed on the above created
table) for the following(and design appropriate interface element):
A. Retrieve a list of all the users and display it in a table.
B. Retrieve a list of users whose name begins with a specific character input by
the user and display it one at a time in a form.
C. Search and display records of the users whose birthday is in a particular month
where month is input by the user.

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