Programming paradigms

A.V.C.COLLEGE OF ENGINEERING
MANNAMPANDAL, MAYILADUTHURAI-609 305
COURSE MATERIAL
FOR THE SUBJECT OF
PROGRAMMING PARADIGMS
SUB NAME : CS2305 PROGRAMMINGPARADIGMS
SEM : VI
DEPARTMENT : COMPUTER SCIENCE AND ENGINEERING
ACADEMIC YEAR : 2013-2013
NAME OF THE FACULTY : PARVATHI.M
DESIGNATION : Asst.Professor
1

A.V.C College of Engineering
Department of Computer Science & Engineering
2013 Odd Semester
SYLLABUS
CS2305 PROGRAMMING PARADIGMS L T P C
3 0 0 3
AIM:
To understand the concepts of object-oriented, event driven, and concurrent
programming paradigms and develop skills in using these paradigms using Java.
UNIT I OBJECT-ORIENTED PROGRAMMING – FUNDAMENTALS 9
Review of OOP - Objects and classes in Java – defining classes – methods - access
specifiers – static members – constructors – finalize method – Arrays – Strings -
Packages – JavaDoc comments
UNIT II OBJECT-ORIENTED PROGRAMMING – INHERITANCE 10
Inheritance – class hierarchy – polymorphism – dynamic binding – final keyword –
abstract classes – the Object class – Reflection – interfaces – object cloning – inner
classes – proxies
UNIT III EVENT-DRIVEN PROGRAMMING 10
Graphics programming – Frame – Components – working with 2D shapes – Using color,
fonts, and images - Basics of event handling – event handlers – adapter classes –
actions – mouse events – AWT event hierarchy – introduction to Swing – Model-View-
Controller design pattern – buttons – layout management – Swing Components
UNIT IV GENERIC PROGRAMMING 8
Motivation for generic programming – generic classes – generic methods – generic code
2

and virtual machine – inheritance and generics – reflection and generics – exceptions –
exception hierarchy – throwing and catching exceptions – Stack Trace Elements -
assertions – logging
UNIT V CONCURRENT PROGRAMMING 8
Multi-threaded programming – interrupting threads – thread states – thread properties –
thread synchronization – thread-safe Collections – Executors – synchronizers – threads
and event-driven programming
TOTAL=45 PERIODS
TEXT BOOK:
1. Cay S. Horstmann and Gary Cornell, “Core Java: Volume I – Fundamentals”, Eighth
Edition, Sun Microsystems Press, 2008.
REFERENCES:
1. K. Arnold and J. Gosling, “The JAVA programming language”, Third edition, Pearson
Education, 2000.
2. Timothy Budd, “Understanding Object-oriented programming with Java”, Updated
Edition, Pearson Education, 2000.
3. C. Thomas Wu, “An introduction to Object-oriented programming with Java”, Fourth
Edition, Tata McGraw-Hill Publishing company Ltd., 2006.
3

CS2305 PROGRAMMING PARADIGMSnit No Title
I Object-oriented Programming – Fundamentals
II Object-oriented Programming – Inheritance
III Event-Driven Programming
IV Generic Programming
V Concurrent Programming
4

CS2305 PROGRAMMING PARADIGMS
UNIT I
OBJECT-ORIENTED PROGRAMMING – FUNDAMENTALS
1) Review of OOP Concepts
a) Encapsulation
b) Inheritance
c) Polymorphism
2) Objects and Classes in Java
3) Language Basics
a) Comments
b) Data Types
c) Variables
d) Statements
e) Functions
4) Defining Classes
5) Methods
6) Access Specifiers
7) Static Members
8) Constructors
a) Parameterized Constructors
b) this Keyword
c) Garbage Collection
9) Finalize Method
10) Arrays
a) One Dimensional Arrays
b) Multi Dimensional Arrays
11) Strings
12) Packages
13) JavaDOC Comments
14) References
1. Review OOP concepts
The object oriented paradigm is built on the foundation laid by the structured
programming concepts.
• The fundamental change in OOP is that a program is designed around the data
being operated upon rather upon the operations themselves.
• Data and its functions are encapsulated into a single entity.
• OOP facilitates creating reusable code that can eventually save a lot of work.
• Polymorphism permits to create multiple definitions for functions.
• Inheritance permits to derive new classes from old ones.
Benefits of object oriented programming
• Data security is enforced.
• Inheritance saves time.
• User defined data types can be easily constructed.
© A.V.C College of Engineering

• Inheritance emphasizes inventions of new data types.
• Large complexity in the software development can be easily managed.
Java History
Java is a general-purpose object oriented programming language developed by Sun
Microsystems of USA in 1991. Originally called ―oak‖ by James Gosling, one of the inventors if
the language. This goal had a strong impact on the development team to make the language
simple, portable, highly reliable and powerful language. Java also adds some new features.
While C++ is a superset of C. Java is neither a superset nor a subset of C or C++.
C++
C Java
Basic concepts of Object oriented programming
• All Java programs are object oriented. Computer programs consist of two elements: code
and data.
• In process oriented model code acting on data. Procedural languages such as C employ
this model.
• To manage increasing complexity object-oriented Programming approach was conceived.
Object-oriented programming organizes a program around its data (that is, objects) and a
set of well-defined interfaces to that data. An object-oriented program can be
characterized as data controlling access to code.
Abstraction
An essential element of object-oriented programming is abstraction. Abstraction refers to
the act of representing essential features without including the background details or
explanations.
For example, people do not think of a car as a set of tens of thousands of individual parts.
They think of it as a well-defined object with its own unique behavior. This abstraction allows
people to use a car to drive to the grocery store without being overwhelmed by the complexity of
the parts that form the car. They can ignore the details of how the engine, transmission, and
braking systems work. Instead they are free to utilize the object as a whole.
The Three OOP Principles
All object-oriented programming languages provide mechanisms to implement the
object-oriented model. They are
• Encapsulation
• Inheritance
• Polymorphism

a) Encapsulation
Encapsulation is the mechanism that binds together code and the data it manipulates, and
keeps both safe from outside interference and misuse.
For example, shifting gears does not turn on the headlights in car, because it encapsulates
the information about all process.
In Java the basis of encapsulation is the class. A class defines the structure and behavior
(data and code) that will be shared by a set of objects. For this reason, objects are sometimes
referred to as instances of a class. Thus, a class is a logical construct and an object has physical
reality.
b) Inheritance
Inheritance is the process by which one object acquires the properties of another object.
This is important because it supports the concept of hierarchical classification. For example
Bird
Attributes:
Feathers
Lay eggs
Flying
bird
Attributes:
-----------
----------
Non flying
bird
Attributes:
-----------
-----------
The bird 'robin ' is a part of the class 'flying bird' which is again a part of the class 'bird'.
The concept of inheritance provides the idea of reusability.
c) Polymorphism
Polymorphism means the ability to take more than one form. Subclasses of a class can
define their own unique behaviors and yet share some of the same functionality of the parent
class.
Shape
Draw()
Circle Object
Draw()
Box Object
Draw()
Triangle Object
Draw()

2. Class and Object
Class defines a new data type. Once defined, this new type can be used to create objects
of that type. Thus, a class is a template for an object, and an object is an instance of a class.
Class
A class is a blueprint or prototype from which objects are created. The entire set of data
and code of an object can be made of a user defined data type with the help of a class. We can
create any number of objects for the same class.

For example the construction of building requires a plan. Without plan we can't construct
building. Here plan acts as class. Building acts as object. Using the same plan we can build any
number of buildings. In the same way we can create any number of objects for the same class.
Class tells the object’s state and behavior. Basically class tells what the object should have.
Object
Object is an instance of class. Object is real world entity which has state, identity and
behavior. It may represent a person, a place, a bank account, a table of data or any item that the
program has to handle.
JAVA Program structure
A file containing Java source code is considered a compilation unit. Such a compilation
unit contains a set of classes and, optionally, a package definition to group related classes
together. Classes contain data and method members that specify the state and behavior of the
objects in your program. Java programs come in two flavors:
1. Standalone applications that have no initial context such as a pre-existing main window
2. Applets for WWW programming
Execution begins when you launch the java virtual machine and tell it to find a particular class.
After finding the class, java executes the enclosed main() method with signature:
public static void main(String[] args)
{
………...
}
Program Execution
Create a source code file using a text editor. The source code is then compiled using the
java compiler javac. Each java program is converted into one or more class files. The content of
the class file is a set of instructions called bytecode to be executed by Java Virtual Machine
(JVM).Java introduces bytecode to create platform independent program. JVM is an interpreter
for bytecode which accepts java bytecode and produces result.
Java Source Code
Java Compiler (Javac)
Java Byte Code (.class)
Java Virtual Machine
Java program Output

3. Language Basics
a) Comments
Java comments make your code easy to understand, modify and use. Java supports three
different types of comment styles.
1.Everything between initial slash –asterisk and ending asterisk-slash is ignored by the java
compiler.(/*……*/)
2.Double slash (//)mark is ignored by java compiler.
3.Everything between initial slash – asterisk - asterisk and ending asterisk-slash is ignored
by the java compiler and another program called JAVADOC.EXE that ships with the
JDK uses these comments to construct HTML documentation files that describe your
packages, classes and methods as well as all the variables used. (/**……*/)
b) Data Types
Java defines eight simple (or elemental) types of data: byte, short, int, long, char, float,
double, and boolean. These can be put in four groups:
• Integers - This group includes byte, short, int, and long, which are for whole valued
signed numbers.
• Floating -point numbers- This group includes float and double, which represent numbers
with fractional precision.
• Characters - This group includes char, which represents symbols in a character set, like
letters and numbers.
• Boolean - This group includes boolean, which is a special type for representing true/false
values.
c) Variables
Variables are locations in memory in which values can be stored. They have a name, a
type, and a value. Before you can use a variable, you have to declare it. After it is declared, you
can then assign values to it.
Java actually has three kinds of variables: instance variables, class variables, and local
variables.
• Instance variables are used to define attributes or the state for a particular object.

• Class v
ariables are similar to instance variables, except their values apply to all
that class’s instances (and to the class itself) rather than having different values
for each object.
• Local variables are declared and used inside method definitions, for example, for
index counters in loops, as temporary variables, or to hold values that you need
only inside the method definition itself.
Although all three kinds of variables are declared in much the same ways, class and
instance variables are accessed and assigned in slightly different ways from local variables.
Scope

• Java has no global variables.
• All variables must be declared within either a class scope or a function scope.
Declaring Variables
For variable declarations, Java syntax is similar to C and C++ syntax. For native types,
the syntax may be summarized as follows:
• One word type name.
• A list of variable names, separated by commas.
• An optional initializer following each variable name.
• Terminated by semicolon.
The following are examples of variable declarations:
• This line of Java code declares a 32-bit integer variable named i:
int i;
• This line declares two 32-bit integer variables named i and j:
int i , j;
• This line declares i and j as above and initializes them:
int i=3, j=4;
d) Statements
Java, like C, is an expression-based language. Expressions must always appear in the
context of statements. A statement consists of an expression followed by a terminating semicolon
(;).
Statements can be made up of zero or more expressions, provided that their combination
makes syntactic sense. Expressions (except for the return value of void methods) have a value
and a type. A terminating semicolon (e.g., 27;) turns it into a legal statement even though it does
not do anything useful. A simple statement consists of an expression and a semicolon. The
semicolon is a required terminator.
4. Defining Class
The class is at the core of Java. It is the logical construct upon which the entire Java
language is built because it defines the shape and nature of an object. As such, the class forms
the basis for object-oriented programming in Java. The entire set of data and code of an object
can be made of a user defined data type with the help of a class. Thus, a class is a template for an
object, and an object is an instance of a class.
The General Form of a Class
The class contains data and the code that operates on that data. A class is declared by use
of the class keyword. The data, or variables, defined within a class are called instance variables.
The code is contained within methods. Collectively, the methods and variables defined within a
class are called members of the class. The general form of a class definition is shown here:
class classname
{
type instance-variable1;
type instance-variable2;

// ...
type instance-variableN;
type methodname1(parameter-list){
// body of method
}
type methodname2(parameter-list) {
// body of method
}
// ...
type methodnameN(parameter-list) {
// body of method
}
}
Here is a class called Box that defines three instance variables: width, height, and depth.
Currently, Box does not contain any methods (but some will be added soon).
class Box
{
double width;
double height;
double depth;
}
Instantiating a class
Class declaration only creates a template; it does not create an actual object. To create a
Box object, you will use a statement like the following:
Box mybox = new Box(); // create a Box object called mybox
• The new operator allocates space for the new object, calls a class constructor and returns
a reference to the object.
• It should be noted that the class and its constructor have the same name.
After this statement executes, mybox will be an instance of Box. Each time you create an
instance of a class, you are creating an object that contains its own copy of each instance variable
defined by the class. Thus, every Box object will contain its own copies of the instance variables
width, height, and depth. To access these variables, you will use the dot (.) operator. The dot
operator links the name of the object with the name of an instance variable. For example, to
assign the width variable of mybox the value 100, you would use the following statement:
mybox.width = 100;
This statement tells the compiler to assign the copy of width that is contained within the
mybox object the value of 100.
5. Methods
Classes usually consist of two things: instance variables and methods.
This is the general form of a method:
Type name (parameter-list)

{
// body of method
}
Type specifies the type of data returned by the method. This can be any valid type,
including class types that you create. If the method does not return a value, its return type must
be void.
The name of the method is specified by name. This can be any legal identifier other than
those already used by other items within the current scope.
The parameter-list is a sequence of type and identifier pairs separated by commas.
Parameters are essentially variables that receive the value of the arguments passed to the method
when it is called. If the method has no parameters, then the parameter list will be empty.
Methods that have a return type other than void return a value to the calling routine using
the following form of the return statement:
return value;
Here, value is the value returned.
Program includes a method inside the box class.
class Box
{
double width;
double height;
double depth;
// display volume of a box
void volume() {
System.out.print("Volume is ");
System.out.println(width * height * depth);
}
}
class BoxDemo3
{
public static void main(String args[]) {
Box mybox1 = new Box();
// assign values to mybox1's instance variables
mybox1.width = 10;
mybox1.height = 20;
mybox1.depth = 15;
/* assign different values to mybox2's instance variables */
mybox2.width = 3;
mybox2.height = 6;
mybox2.depth = 9;
// display volume of first box
mybox1.volume();
// display volume of second box

mybox2.volume();
}
}
This program generates the following output.
THE JAVA LANGUAGE
Volume is 3000.0
Volume is 162.0
The mybox1.volume() invokes the volume( ) method on mybox1. That is, it calls
volume( ) relative to the mybox1 object, using the object’s name followed by the dot operator.
Thus, the call to mybox1.volume( ) displays the volume of the box defined by mybox1, and the
call to mybox2.volume( ) displays the volume of the box defined by mybox2. Each time
volume( ) is invoked, it displays the volume for the specified box.
6. Access specifiers
Encapsulation provides another important attribute: access control. Through
encapsulation, you can control what parts of a program can access the members of a class. By
controlling access, you can prevent misuse.
How a member can be accessed is determined by the access specifier that modifies its
declaration. Java supplies a rich set of access specifiers. Some aspects of access control are
related mostly to inheritance or packages. (A package is, essentially, a grouping of classes.)
Java’s access specifiers are
 Public
 Private
 Protected
 default access level.
Public
When a member of a class is modified by the public specifier, then that member can be
accessed by any other code. So main( ) has always been preceded by the public specifier.
Classes can be declared public. A public class is accessible by any other Java class. A
class that is not declared public has package access, which means that only classes within the
same package may access it. Class members labeled public are accessible to all other classes.
Private
When a member of a class is specified as private, then that member can only be accessed
by other members of its class.
Class members can be declared public or private to enforce proper encapsulation. Certain
data elements or methods that are necessary for the class’s internal behavior should be protected
from access by outside classes. These should be declared private. A class member that has been
declared as private will remain private to its class. It is not accessible by any code outside its
class, including subclasses.
Protected
Any member that is declared protected is accessible only by a class that is derived from
the current class or is in the same package as the containing class.

default access level
When no access specifier is used, then by default the member of a class is public within
its own package, but cannot be accessed outside of its package.
7. Static Members
Static Variables
If you define a field as static, then there is only one such field per class. In contrast, each
object has its own copy of all instance fields. For example, let's suppose we want to assign a
unique identification number to each employee. We add an instance field id and a static field
nextId to the Employee class:
class Employee
{
...
private int id;
private static int nextId = 1;
}
Now, every employee object has its own id field, but there is only one nextId field that is shared
among all instances of the class. Let's put it another way. If there are one thousand objects of the
Employee class, then there are one thousand instance fields id, one for each object. But there is a
single static field nextId. Even if there are no employee objects, the static field nextId is present.
It belongs to the class, not to any individual object.
Constants

Static variables are quite rare. However, static constants are more common. For example,
the Math class defines a static constant:
public class Math
{
...
public static final double PI = 3.14159265358979323846;

...
}
You can access this constant in your programs as Math.PI. If the keyword static had been
omitted, then PI would have been an instance field of the Math class. That is, you would need an
object of the Math class to access PI, and every object would have its own copy of PI. Another
static constant that you have used many times is System.out. It is declared in the System class as:
public class System
{
...
public static final PrintStream out = . . .;
...
}
As we mentioned several times, it is never a good idea to have public fields because everyone
can modify them. However, public constants (that is, final fields) are ok. Since out has been
declared as final, you cannot reassign another print stream to it:
out = new PrintStream(. . .); // ERROR--out is final
Static Methods
Static methods are methods that do not operate on objects. For example, the pow method
of the Math class is a static method. The expression:
Math.pow(x, y)
Computes the power xy. It does not use any Math object to carry out its task. In other words, it
has no implicit parameter. In other words, you can think of static methods as methods that don't
have a this parameter. Because static methods don't operate on objects, you cannot access
instance fields from a static method. But static methods can access the static fields in their class.
Here is an example of such a static method:
public static int getNextId()
{
return nextId; // returns static field
}
To call this method, you supply the name of the class:
int n = Employee.getNextId();
Could you have omitted the keyword static for this method? Yes, but then you would need to
have an object reference of type Employee to invoke the method. You use static methods in two
situations:
1. When a method doesn't need to access the object state because all needed
parameters are supplied as explicit parameters (example: Math.pow)
2. When a method only needs to access static fields of the class (example:
Employee.getNextId)
8. Constructors
A constructor is a special method whose purpose is to construct and initialize objects.
Constructors always have the same name as the class name.
The constructor is automatically called immediately after the object is created, before the
new operator completes.

new Box( ) is calling the Box( ) constructor. When you do not explicitly define a
constructor for a class, then Java creates a default constructor for the class. The default
constructor automatically initializes all instance variables to zero.
There is an important difference between constructors and other methods: A constructor
can only be called in conjunction with the new operator. You can't apply a constructor to an
existing object to reset the instance fields.
Features of constructor
 A constructor has the same name as the class.
 A class can have more than one constructor.
 A constructor may take zero, one, or more parameters.
 A constructor has no return value.
 A constructor is always called with the new operator.
a) Parameterized Constructors
Add parameters to the constructor.
class Box
{
double width;
double height;
double depth;
// This is the constructor for Box.
Box(double w, double h, double d) {
width = w;
height = h;
depth = d;
}
// compute and return volume
double volume() {
return width * height * depth;
}
}
class BoxDemo7
{
// declare, allocate, and initialize Box objects
Box mybox1 = new Box(10, 20, 15);
double vol;
// get volume of first box
vol = mybox1.volume();
System.out.println("Volume is " + vol);
}
}
The output from this program is shown here:
Volume is 3000.0

Object is initialized as specified in the parameters to its constructor.
Box mybox1 = new Box(10, 20, 15);
The values 10, 20, and 15 are passed to the Box( ) constructor when new creates the object.
Thus, mybox1’s copy of width, height, and depth will contain the values 10, 20, and 15,
respectively.
b) “this” Keyword
this can be used inside any method to refer to the current object. this keyword has two
meanings:
 to denote a reference to the implicit parameter
 to call another constructor of the same class.
// A redundant use of this.
Box(double w, double h, double d)
{
this.width = w;
this.height = h;
this.depth = d;
}
c) Garbage Collection
The purpose of garbage collection is to identify and discard objects that are no longer
needed by a program so that their resources can be reclaimed and reused. A Java object is subject
to garbage collection when it becomes unreachable to the program in which it is used.
9. Finalizer method
Finalizer methods are like the opposite of constructor methods; whereas a constructor
method is used to initialize an object, finalizer methods are called just before the object is
garbage collected and its memory reclaimed. To create a finalizer method, include a method with
the following signature in your class definition:
void finalize() {
...
}
Inside the body of that finalize() method, include any cleaning up you want to do for that
object. Before you start using finalizer methods extensively in your Java programs, however, be
aware that finalizer methods have several very important restrictions. First of all, the finalizer
method is not guaranteed to be called until the object’s memory is actually reclaimed, which may
be some time after you’ve removed all references to that object.
However, calling finalize() does not trigger an object to be garbage-collected. Only
removing all references to an object will cause it to be marked for deleting, and even then, Java
may or may not call the finalize() method itself—regardless of whether or not you’ve already
called it. Finalizer methods are best used for optimizing the removal of an object—for example,
by removing references to other objects, by cleaning up things that object may have touched, or
for other optional behaviors that may make it easier for that object to be removed. In most cases,
you may not need to use finalize() at all.

Some object-oriented programming languages, notably C++, have explicit destructor
methods for any cleanup code that may be needed when an object is no longer used. The most
common activity in a destructor is reclaiming the memory set aside for objects. Since Java does
automatic garbage collection, manual memory reclamation is not needed, and Java does not
support destructors. Of course, some objects utilize a resource other than memory, such as a file
or a handle to another object that uses system resources. In this case, it is important that the
resource be reclaimed and recycled when it is no longer needed. You can add a finalize method
to any class. The finalize method will be called before the garbage collector sweeps away the
object. In practice, do not rely on the finalize method for recycling any resources that are in short
supply—you simply cannot know when this method will be called. If a resource needs to be
closed as soon as you have finished using it, you need to manage it manually. Add a dispose
method that you call to clean up what needs cleaning. Just as importantly, if a class you use has a
dispose method, you will want to call it when you are done with the object. In particular, if your
class has an instance field that has a dispose method, provide a dispose method that disposes of
the instance fields.
10. Arrays
An array is a group of like-typed variables that are referred to by a common name. Arrays
of any type can be created and may have one or more dimensions. A specific element in an array
is accessed by its index. Arrays offer a convenient means of grouping related information.
Arrays are ordered collections of identical objects that can be accessed via an index. Java
arrays have their own behavior that is encapsulated into their definition when the compiler
creates them. Since arrays are objects, array variables behave like class-type variables. It is
important to distinguish between the array variable and the array instance to which it refers.
• Declaring an array only declares the array variable.
• To instantiate the array, the new operator must be used with the [] operator to
enclose the array size. The array size can be any integer expression.
The following code declares an array variable and initializes it to null:
char data[] = null;
Array Constants
The declaration of an array must include its type, but not its size. An array initializer is
either a new expression that evaluates to the correct array type, or a list of initial element values
enclosed in { }. The following array constant provides initial values for its elements:
int[] int_array = {1, 3, 4, 15, 0};
Using Arrays
Array elements can be accessed using an index in square brackets [n], where the index
must be an integer. Arrays start with index number 0, not 1. The index can be thought of as an
offset from the beginning of the array. The index may not be less than zero or greater than the
declared size. If the array is declared size n, the index must be in the range 0 to n-1. Any attempt
to index an array with an illegal value will cause an exception to be thrown. All arrays have a
data field called length that indicates its size.
int ia[] = new int[100];
for (int i = 0; i < ia.length; i++)
{

ia[i] = i * i;
}
Copying Array Elements
The library method System.arraycopy() is useful for copying a number of elements from
one array to another. The method can be used on any type of array and is declared as follows:
public static void arraycopy (Object src, int src_position, Object dst, int dst_position, int
length)
The method copies elements from the given source array, beginning at the specified
position to the destination array at the specified position. It copies the number of elements
specified by the length argument. The destination array must already be allocated. Any type of
array may be copied. If range exceeds bounds of either array, a run-time error results.
Arrays in Java are in between a class and a data type although they are implemented as a
class internally by Java.
char data[] = null;
char[] data = null;
int length = 60;
char[] data = new char [length];
a) One-Dimensional Arrays
A one-dimensional array is a list of like-typed variables. Array is created by following steps.
1. Create an array variable of the desired type. The general form of a one dimensional array
declaration is
type var-name[ ];
2. Allocate memory for array.
Method1: The general form of new as it applies to one-dimensional arrays appears as
follows:
array-var = new type[size];
The elements in the array allocated by new will automatically be initialized to zero.
Method2: Arrays can be initialized when they are declared. The process is much the
same as that used to initialize the simple types. An array initializer is a list of comma-
separated expressions surrounded by curly braces. The commas separate the values of the
array elements. The array will automatically be created large enough to hold the number
of elements you specify in the array initializer. There is no need to use new. For example,
to store the number of days in each month, the following code creates an initialized array
of integers:
// An improved version of the previous program.
class AutoArray {
int month_days[] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31,30, 31 };
System.out.println("April has " + month_days[3] + " days.");
}
}

b) Multidimensional Arrays
In Java, multidimensional arrays are actually arrays of arrays. These, as you might
expect, look and act like regular multidimensional arrays. However, as you will see, there are a
couple of subtle differences. To declare a multidimensional array variable, specify each
additional index using another set of square brackets. For example, the following declares a two-
dimensional array variable called twoD.
int twoD[][] = new int[4][5];
This allocates a 4 by 5 array and assigns it to twoD. Internally this matrix is implemented as an
array of arrays of int.
There is a second form that may be used to declare an array:
type[ ] var-name;
Here, the square brackets follow the type specifier, and not the name of the array variable. For
example, the following two declarations are equivalent:
int al[] = new int[3];
int[] a2 = new int[3];
The following declarations are also equivalent
11. String objects
The Java String class (java.lang.String) is a class of object that represents a character
array of arbitrary length. While this external class can be used to handle string objects, Java
integrates internal, built-in strings into the language.

An important attribute of the String class is that once a string object is constructed, its
value cannot change (note that it is the value of an object that cannot change, not that of a string
variable, which is just a reference to a string object). All String data members are private, and no
string method modifies the string’s value.
String Methods
Although a string represents an array, standard array syntax cannot be used to inquire into
it. These are detailed in the below Table.
String Comparison
String comparison methods listed in below Table.

String Searching
The String class also provides methods that search a string for the occurrence of a single
character or substring. These return the index of the matching substring or character if found, or -
1 if not found.
 int indexOf (char ch)
 int indexOf (char ch, int begin)
 int lastIndexOf (char ch)
 int lastIndexOf (char ch, int fromIndex)
 int indexOf (String str)
 int indexOf (String str, int begin)
 int lastIndexOf (String str)
 int lastIndexOf (String str, int fromIndex)
The following example shows the usage of these functions:
if (s1.indexOf (’:’) >= 0)
{
…
}
String suffix =

s1.substring (s1.lastIndexOf (’.’));
int spaceCount = 0;
int index = s1.indexOf (’ ’);
while (index >= 0)
{
++spaceCount;
index = s1.indexOf (’ ’, index + 1);

}
int index = s1.indexOf (―that );‖
String Concatenation
The String class provides a method for concatenating two strings:
String concat (String otherString)
The + and += String operators are more commonly used: The Java compiler recognizes the + and
+= operators as String operators. For each + expression, the compiler generates calls to methods
that carry out the concatentation. For each += expression, the compiler generates calls to
methods that carry out the concatenation and assignment.
Converting Objects To Strings
The String + operator accepts a non-string operand, provided the other operand is a
string. The action of the + operator on non-string operands is to convert the non-string to a string,
then to do the concatenation. Operands of native types are converted to string by formatting their
values. Operands of class types are converted to a string by the method toString() that is defined
for all classes. Any object or value can be converted to a string by explicitly using one of the
static valueOf() methods defined in class String:
String str = String.valueOf (obj);
If the argument to valueOf() is of class type, then valueOf() calls that object’s toString() method.
Any class can define its own toString() method, or just rely on the default. The output produced
by toString() is suitable for debugging and diagnostics. It is not meant to be an elaborate text
representation of the object, nor is it meant to be parsed. These conversion rules also apply to the
right-hand side of the String += operator.
Converting Strings To Numbers
Methods from the various wrapper classes, such as Integer and Double, can be used to
convert numerical strings to numbers.
The wrapper classes contain static methods such as parseInt() which convert a string to its
own internal data type.
12. Packages
Java allows you to group classes in a collection called a package. A class can use all
classes from its own package and all public classes from other packages.
You can import a specific class or the whole package. You place import statements at the
top of your source files (but below any package statements). For example, you can import all
classes in the java.util package with the statement:
import java.util.*;
Adding a class into a package
To place classes inside a package, you must put the name of the package at the top of
your source file, before the code that defines the classes in the package. For example,
package com.horstmann.corejava;
public class Employee

{
...
}
Package scope
• Public features can be used by any class.
• Private features can only be used by the class that defines them.
• If you don't specify either public or private, then the feature (that is, the class, method, or
variable) can be accessed by all methods in the same package.
13. Documentation Comments
The Java SDK contains a very useful tool, called javadoc, that generates HTML
documentation from your source files. If you add comments that start with the special delimiter
/** to your source code, you too can produce professional-looking documentation easily. This is
a very nice scheme because it lets you keep your code and documentation in one place. If you
put your documentation into a separate file, then you probably know that the code and comments
tend to diverge over time. But since the documentation comments are in the same file as the
source code, it is an easy matter to update both and run javadoc again.
How to Insert Comments
The javadoc utility extracts information for the following items:
• Packages
• Public classes and interfaces
• Public and protected methods
• Public and protected fields
You can (and should) supply a comment for each of these features. Each comment is
placed immediately above the feature it describes. A comment starts with a /** and ends with a
*/. Each /** . . . */ documentation comment contains free-form text followed by tags. A tag starts
with an @, such as @author or @param. The first sentence of the free-form text should be a
summary statement. The javadoc utility automatically generates summary pages that extract
these sentences. In the free-form text, you can use HTML modifiers such as <em>...</em> for
emphasis, <code>...</code> for a monospaced ―typewriter‖ font, <strong>...</strong> for strong
emphasis, and even <img ...> to include an image. You should, however, stay away from
heading <h1> or rules <hr> since they can interfere with the formatting of the document.
Class Comments
The class comment must be placed after any import statements, directly before the class
definition. Here is an example of a class comment:
/**
A <code>Card</code> object represents a playing card, such as "Queen of Hearts". A
card has a suit (Diamond, Heart, Spade or Club) and a value (1 = Ace, 2 . . . 10, 11 =
Jack, 12 = Queen, 13 = King).
*/
public class Card

{
...
}
Method Comments
Each method comment must immediately precede the method that it describes. In
addition to the general-purpose tags, you can use the following tags:
@param variable description
This tag adds an entry to the ―parameters‖ section of the current method. The description can
span multiple lines and can use HTML tags. All @param tags for one method must be kept
together.
@return description
This tag adds a ―returns‖ section to the current method. The description can span multiple lines
and can use HTML tags.
@throws class description
Field Comments
You only need to document public fields—generally that means static constants. For
example,
/**
The "Hearts" card suit
*/
public static final int HEARTS = 1;
General Comments
The following tags can be used in class documentation comments.
@author name
This tag makes an ―author‖ entry. You can have multiple @author tags, one for each author.
@version text
How to Extract Comments
Here, docDirectory is the name of the directory where you want the HTML files to go. Follow
these steps:
1. Change to the directory that contains the source files you want to document. If you have
nested packages to document, such as com.horstmann.corejava, you must be in the
directory that contains the subdirectory com. (This is the directory that contains the
overview.html file, if you supplied one.)
2. Run the command javadoc -d docDirectory nameOfPackage for a single package. Or run
javadoc -d docDirectory nameOfPackage1 nameOfPackage2... to document multiple
packages. If your files are in the default package, then run javadoc -d docDirectory *.java
instead. If you omit the -d docDirectory option, then the HTML files are extracted to the
current directory. That can get messy, and we don't recommend it. The javadoc program
can be fine-tuned by numerous command-line options. For example, you can use the -
author and -version options to include the @author and @version tags in the
documentation. (By default, they are omitted.)

14. References
1. Cay S. Horstmann and Gary Cornell, ―Core Java: Volume I – Fundamentals ,‖ Eighth
Edition, Sun Microsystems Press, 2008.
2. Herbert Schildt ―JAVA2:The complete reference‖ Fifth Edition, McGraw-Hill/Osborne.
3. http://java.sun.com

UNIT II OBJECT-ORIENTED PROGRAMMING – INHERITANCE
1. Inheritance
1.1. Member Access And Inheritance
1.2. Super Keyword
2. Class Hierarchy
3. Polymorphism
3.1. Overridden Methods
3.2. Overloaded Methods
4. Dynamic Binding
4.1. Dynamic Binding
4.2. Static Binding
5. Final Keyword
6. Abstract Classes
6.1. Abstract Methods
7. The Object Class
8. Reflection
9. Interfaces
10. Object Cloning
11. Inner Classes
12. Proxies
Inheritance
Inheritance is a process of making a new class that derives from an existing class. The
existing class is called the superclass, base class, or parent class. The new class is called the
subclass, derived class, or child class.
Therefore, a subclass is a specialized version of a superclass. It inherits all of the
instance variables and methods defined by the superclass and add its own, unique elements.
Subclasses of a class can define their own unique behaviors and yet share some of the
same functionality of the parent class.
To inherit a class, you simply incorporate the definition of one class into another by using
the extends keyword. The general form of a class declaration that inherits a superclass is shown
here:
class subclass-name extends superclass-name
{
// body of class
}
You can only specify one superclass for any subclass that you create. Java does not
support the inheritance of multiple superclasses into a single subclass.
Protected features in Java are visible to all subclasses as well as all other classes in the
same package.

Member Access and Inheritance
A class member that has been declared as private will remain private to its class. It is not
accessible by any code outside its class, including subclasses.
Super keyword
Super is a special keyword that directs the compiler to invoke the superclass method.
super has two general forms.
 to invoke a superclass constructor.
 to invoke a superclass members(variables &methods). invoke a superclass
constructor
Invoke superclass constructor:
• A subclass can call a constructor method defined by its superclass by use of the following
form of super:
super(parameter-list);
• Here, parameter-list specifies any parameters needed by the constructor in the superclass.
• super( ) must always be the first statement executed inside a subclass constructor.
• The compiler implicitly calls the base class’s no-parameter constructor or default
constructor.
• If the superclass has parameterized constructor and the subclass constructor does not call
superclass constructor explicitly, then the Java compiler reports an error.
Invoke superclass members:
• Super always refers to the superclass of the subclass in which it is used. This usage has
the following general form:
super.member;
• Here, member can be either a method or an instance variable. This second form of super
is most applicable to situations in which member names of a subclass hide members by
the same name in the superclass.
• If a parent class contains a finalize() method, it must be called explicitly by the derived
class’s finalize() method.
super.finalize();
When Constructors are Called
Constructors are called in order of derivation, from superclass to subclass. Because a
superclass has no knowledge of any subclass, any initialization it needs to perform is separate
from and possibly prerequisite to any initialization performed by the subclass. Therefore, it must
be executed first.
CLASS HIERARCHY
The collection of all classes extending from a common superclass is called an inheritance
hierarchy; the path from a particular class to its ancestors in the inheritance hierarchy is its
inheritance chain.
Simple class hierarchies consist of only a superclass and a subclass. But you can build
hierarchies that contain as many layers of inheritance as you like.

For example, create three classes called A, B, and C, C can be a subclass of B, which is a
subclass of A. When this type of situation occurs, each subclass inherits all of the traits found in
all of its superclasses. In this case, C inherits all aspects of B and A.
POLYMORPHISM
Polymorphism means the ability of methods to behave differently based on the kinds of
input.
Types of polymorphism
• Method Overloading
• Method overriding
Overloaded methods
Overloaded methods are methods with the same name but different method signature
(either a different number of parameters or different types in the parameter list).
public class Test{
public static void main(String arg[]){
A a=new A();
a.display();
B b=new B();
b.display("Hello");
}
}
class A{
void display(){
System.out.println("Hai");
}
}
class B extends A{
void display(String s){
System.out.println(s);
}
}
Output
Hai
Hello
Overridden methods
The process of a subclass redefining a method contained in the superclass (with the same
parameter types) is called overriding the method.
Overridden methods allow Java to support run time polymorphism. Whenever a method
is called for a subclass object, the compiler calls the overriding version instead of the superclass
version. The version of the method defined by the superclass will be hidden.

Call to an overridden method is resolved at run time, rather than compile time. Superclass
reference variable can refer to a subclass object. Java uses this fact to resolve calls to overridden
methods at run time. When an overridden method is called through a superclass reference, Java
determines which version of that method to execute based upon the type of the object being
referred to at the time the call occurs. This determination is made at run time.
class Dispatch {
A a = new A(); // object of type A
B b = new B(); // object of type B
C c = new C(); // object of type C
A r; // obtain a reference of type A
r = a; // r refers to an A object
r.callme(); // calls A's version of callme
r = b; // r refers to a B object
r.callme(); // calls B's version of callme
r = c; // r refers to a C object
r.callme(); // calls C's version of callme
}
}
When you override a method, the subclass method must be at least as visible as the
superclass method.
In particular, if the superclass method is public, then the subclass method must also be
declared as public. It is a common error to accidentally omit the public specifier for the subclass
method. Then the compiler complains that you try to supply a weaker access privilege.
public class Test1{
A a=new A();
a.display();
B b=new B();
b.display();
}
}
class A{
protected void display(){
}
}
class B extends A{
public void display(){
System.out.println("Hello");
}
}

Output
Hai
Hello
Methods labeled final, private, or static are not subject to dynamic lookup because they
may not be overridden. private methods are simply not inherited because they would never be
callable anyway. static methods apply to a particular class’s static data and thus make no sense in
a derivation. final methods are those designated as not-overridable for reasons of complexity or
safety.
public class Test1{
A a1=new A();
a1.display();
A a2=new B();
a2.display();
}
}
class A{
void display(){
}
}
class B extends A{
void display(){
}
}
Output
Hai
Hello
DYNAMIC BINDING
Selecting the appropriate method at runtime is called dynamic binding. Dynamic Binding
refers to the case where compiler is not able to resolve the call and the binding is done at runtime
only.
• All the instance methods in Java follow dynamic binding.
Dynamic binding has a very important property:

It makes programs extensible without recompiling the existing code.
Suppose a new class is added, and there is the possibility that the variable refers to an
object of that class. The code contains the method invoking statement of that class need not be
recompiled. The method is called automatically if the object happens to refer to the class.

Dynamic Binding or Late Binding
It is important to understand what happens when a method call is applied to an object. Here
are the details:
1. The compiler looks at the declared type of the object and the method name. The compiler
knows all possible candidates for the method to be called.
2. Next, the compiler determines the types of the parameters that are supplied in the method
call. If among all the methods called fun there is a unique method whose parameter types
are a best match for the supplied parameters, then that method is chosen to be called. This
process is called overloading resolution.
3. If the method is private, static, final, or a constructor, then the compiler knows exactly
which method to call.
4. When the program runs and uses dynamic binding to call a method, then the virtual
machine must call the version of the method that is appropriate for the actual type of the
object. The virtual machine precomputes a method table for each class that lists all
method signatures and the actual methods to be called. When a method is actually called,
the virtual machine simply makes a table lookup. This is used to reduce the time
consumed by searching process.
STATIC BINDING OR EARLY BINDING
If the compiler can resolve the binding at the compile time only then such a binding is
called Static Binding or Early Binding. Resolve the call and binding at compile time.
If the method is private, static, final, or a constructor, then the compiler knows exactly
which method to call. This is called static binding.
• All the member variables in Java follow static binding.
• All the static method calls are resolved at compile time itself.
• All private methods are resolved at compile time itself.
FINAL KEYWORD
The keyword final has three uses.
 Used to create the equivalent of a named constant.
 Used to Prevent Overriding
 Used to Prevent Inheritance
Named constant
A variable can be declared as final. Doing so prevents its contents from being modified.
This means that you must initialize a final variable when it is declared. For example:
final int constant = 1;
Variables declared as final do not occupy memory on a per-instance basis. Thus, a final variable
is essentially a constant. The keyword final can also be applied to methods, but its meaning is
substantially different than when it is applied to variables. Attempts to change it will generate
either a compile-time error or an exception.

Using final to Prevent Overriding
Methods declared as final cannot be overridden.The syntax is simple, just put the
keyword final after the access specifier and before the return type like this:
class A
{
final void meth() {
System.out.println("This is a final method.");
}
}
class B extends A
{
void meth() { // ERROR! Can't override.
System.out.println("Illegal!");
}
}
Normally, Java resolves calls to methods dynamically, at run time. This is called late
binding. However, since final methods cannot be overridden, a call to one can be resolved at
compile time. This is called early binding.
Using final to Prevent Inheritance
Declaring a class as final implicitly declares all of its methods as final. So it prevents a
class from being inherited. To do this, precede the class declaration with final.
It is illegal to declare a class as both abstract and final since an abstract class is
incomplete by itself and relies upon its subclasses to provide complete implementations.
Here is an example of a final class:
final class A
{
// ...
}
// The following class is illegal.
class B extends A
{ // ERROR! Can't subclass A
// ...
}
ABSTRACT CLASSES
An abstract class is a type of class that is not allowed to be instantiated. The only reason
it exists is to be extended. Abstract classes contain methods and variables common to all the
subclasses, but the abstract class itself is of a type that will not be used directly. Even a single
abstract method requires that a class be marked abstract.

To declare a class abstract, you simply use the abstract keyword in front of the class
keyword at the beginning of the class declaration.
abstract class classname
{
public abstract type methodname();
// no implementation required
……..
}
There can be no objects of an abstract class. That is, an abstract class cannot be directly
instantiated with the new operator. Such objects would be useless, because an abstract class is
not fully defined.
Also, you cannot declare abstract constructors, or abstract static methods. Any subclass
of an abstract class must either implement all of the abstract methods in the superclass, or be
itself declared abstract.
Here is a simple example of a class with an abstract method, followed by a class which
implements that method:
// A Simple demonstration of abstract.
abstract class A
{
abstract void callme();// concrete methods are still allowed in abstract classes
void callmetoo() {
System.out.println("This is a concrete method.");
}
}
class B extends A
{
void callme() {
System.out.println("B's implementation of callme.");
}
}
class AbstractDemo
{
B b = new B();
b.callme();
b.callmetoo();
}
}
That is, sometimes you will want to create a superclass that only defines a generalized
form that will be shared by all of its subclasses, leaving it to each subclass to fill in the details.
Such a class determines the nature of the methods that the subclasses must implement. You can
require that certain methods be overridden by subclasses by specifying the abstract type

modifier. These methods are sometimes referred to as subclasser responsibility because they
have no implementation specified in the superclass.
Thus, a subclass must override them—it cannot simply use the version defined in the
superclass.
Abstract methods
An abstract method is a method declaration that contains no functional code. The reason for
using an abstract method is to ensure that subclasses of this class will include an implementation
of this method. Any concrete class (that is, a class that is not abstract, and therefore capable of
being instantiated) must implement all abstract methods it has inherited.
Methods declared with the keyword abstract define a skeleton for a method but do not
implement it. This requires a derived class to provide the code for this class.
A class with one or more abstract methods must itself be declared abstract and cannot be
instantiated. It can only be used for derivation.
To declare an abstract method, use this general form:
abstract type name(parameter-list);
UAGE
But while an abstract class can define both abstract and nonabstract methods, an interface can
have only abstract methods. Interface as being similar to an abstract class with no instance fields.
Interfaces
An interface is a collection of method definitions (without implementations) and constant values.
Defining an Interface
This is the general form of an interface:
 An interface must be declared with the keyword interface.
access interface name {
return-type method-name(parameter-list);
type final-varname = value;
}
 It is also possible to declare that an interface is protected so that it can only be
implemented by classes in a particular package. However this is very unusual.
Rules for interface constants. They must always be
 public
 static
 final
Once the value has been assigned, the value can never be modified. The assignment happens in
the interface itself (where the constant is declared), so the implementing class can access it and
use it, but as a read-only value.
To make a class implement an interface, have to carry out two steps:

 Declare that your class intends to implement the given interface.
 Supply definitions for all methods in the interface.
To declare that a class implements an interface, use the implements keyword:
access class classname implements interfacename
{
//definitions for all methods in the interface
}
Implementation classes must adhere to the same rules for method implementation as a class
extending an abstract class. In order to be a legal implementation class, a nonabstract
implementation class must do the following:
 When you implement an interface method, method must be declared as public. (The
access level can be more accessible than that of the overridden method.)
 Type signature of the implementing method must match exactly the type signature
specified in the interface definition. (The argument list and return type must exactly
match that of the overridden method.)
 A class can implement one or more interfaces.
 Partial Implementations: If a class includes an interface but does not fully implement the
methods defined by that interface, then that class must be declared as abstract.
Inner Classes
• An inner class is a class that is defined inside another class.
• Inner classes let you make one class a member of another class. Just as classes have
member variables and methods, a class can also have member classes.
Regular Inner Class
You define an inner class within the curly braces of the outer class, as follows:
class MyOuter {
class MyInner { }
}
And if you compile it, %javac MyOuter.java , you’ll end up with two class files:
MyOuter.class
MyOuter$MyInner.class
The inner class is still, in the end, a separate class, so a class file is generated. But the
inner class file isn’t accessible to you in the usual way. The only way you can access the inner
class is through a live instance of the outer class.

Instantiating an Inner Class
To instantiate an instance of an inner class, you must have an instance of the outer class.
An inner class instance can never stand alone without a direct relationship with a specific
instance of the outer class.
Instantiating an Inner Class from Within Code in the Outer Class
From inside the outer class instance code, use the inner class name in the normal way:
class MyOuter {
private int x = 7;
MyInner mi = new MyInner();
class MyInner {
public void seeOuter() {
System.out.println("Outer x is " + x);
}
}
MyOuter mo=new MyOuter();
mo.mi.seeOuter();
}
}
Output:
Outer x is 7
Method-Local Inner Classes
 A method-local inner class is defined within a method of the enclosing class.
class MyOuter {
void inner()
{
final int c=9;
class MyInner {
int x=5;
public void display() {
System.out.println("Inner x is " + x);
System.out.println("Inner c is " + c);
}
}
MyInner mi = new MyInner();
mi.display();
}
MyOuter mo = new MyOuter();
mo.inner();
}
}

Output: x is 5
c is 9
Anonymous Inner Classes
 Anonymous inner classes have no name, and their type must be either a subclass of the
named type or an implementer of the named interface.
 An anonymous inner class is always created as part of a statement, so the syntax will end
the class definition with a curly brace, followed by a closing parenthesis to end the
method call, followed by a semicolon to end the statement: });
 An anonymous inner class can extend one subclass, or implement one interface. It cannot
both extend a class and implement an interface, nor can it implement more than one
interface.
public class Test{
B b=new B();
b.ob.display();
}
}
class A{
void display(){
}
}
class B {
A ob=new A(){
void display(){
}
};
}
Output: Hello
And if you compile it, %javac Test.java , you’ll end up with two class files:
A.class
B.class
B$1.class
Test.class
Static Nested Classes
 Static nested classes are inner classes marked with the static modifier.
 Technically, a static nested class is not an inner class, but instead is considered a top-
level nested class.

 Because the nested class is static, it does not share any special relationship with an
instance of the outer class. In fact, you don’t need an instance of the outer class to
instantiate a static nested class.
 Instantiating a static nested class requires using both the outer and nested class names as
follows:
BigOuter.Nested n = new BigOuter.Nested();
 A static nested class cannot access nonstatic members of the outer class, since it does not
have an implicit reference to any outer instance (in other words, the nested class instance
does not get an outer this reference).
public class Test{
A.B b=new A.B();
b.display();
}}
class A {
static class B {
int m=5;
void display(){
System.out.println("m="+m);
}
}
}
Output: m=5
The Object Class - The Cosmic Superclass
The Object class sits at the top of the class hierarchy tree in the Java development
environment. The Object class is the ultimate ancestor
Every class in Java extends Object class.
The Object class defines the basic state and behavior that all objects must have, such as
the ability to compare with another object, to convert to a string, to wait on a condition variable,
to notify other objects that a condition variable has changed, and to return the object's class.
Object defines the following methods, which means that they are available in every
object.
Reflection
• Reflection is the ability of the software to analyze itself at runtime.
• Reflection is provided by the java.lang.reflect package and elements in class.
• This mechanism is helpful to tool builders, not application programmers.
The reflection mechanism is extremely used to

 Analyze the capabilities of classes at run time
 Inspect objects at run time
 Implement generic array manipulation code
Analyze the capabilities of classes at run time - Examine the structure of class.
Java.lang.Class
Field[] getFields()
Method[] getMethods()
Constructor[] getConstructors()
Return an array of public fields, methods
and constructors that the class supports. This
includes all public members of super class.
Field[] getDeclaredFields()
Method[] getDeclaredMethods()
Constructor[] getDeclaredConstructors()
Return an array of fields, methods and
constructors that are declared in the class.
This includes private, protected and public
members of class but not members of super
class.
Java.lang.reflect
Field Method Constructor
Methods (Field, Method & Constructor):
• String getName() – return the name of the item.
• int getModifiers()- return an integer, that describes the modifier.
Field

• Provide information about fields.
• The getFields method returns an array containing Field objects for the public fields.
• The getDeclaredField method returns an array of Field objects for all fields. The methods
return an array of length 0 if there are no such fields.
import java.lang.reflect.*;

class Test{
public int var1;
private int var2;
protected int var3;
int var4;
}
public class FieldDemo{
public static void main(String args[])throws Exception{
Class c=Class.forName("Test");
Field f[]=c.getFields();
Field fdec[]=c.getDeclaredFields();
System.out.println("public Fields:");
for(int i=0;i<f.length;i++)
System.out.println(f[i]);
System.out.println("All Fields:");
for(int i=0;i<fdec.length;i++)
System.out.println(fdec[i]);
}
}
Output:
public Fields:
public int Test.var1
All Fields:
public int Test.var1
private int Test.var2
protected int Test.var3
int Test.var4
Method
• Provides information about method
• The getMethods() method return an array containing Method objects that give you all the
public methods.
• The getDeclaredMethods () return all methods of the class or interface. This includes
those inherited from classes or interfaces above it in the inheritance chain.
class Test{
public void method1()
{}
protected void method2()
{}
private void method3()
{}
void method4()
{}
}

public class MethodDemo{
public static void main(String args[])throws Exception{
Class c=Class.forName("Test");
Method m[]=c.getMethods();
Method mdec[]=c.getDeclaredMethods();
System.out.println("public Methods of class Test & its Super class:");
for(int i=0;i<m.length;i++)
System.out.println(m[i].getName());
System.out.println("All Methods:");
for(int i=0;i<mdec.length;i++)
System.out.println(mdec[i].getName());
}
}
Output:
public Methods of class Test & its Super
class:
method1
hashCode
getClass
wait
equals
notify
notifyAll
toString
All Methods:
method1
method2
method3
method4

Constructor
• Provide information about constructors
• getConstructors () method return an array containing Constructor objects that give you all
the public constructors
• getDeclaredConstructors () method return all constructors of the class represented by the
Class object.
Using Reflection to Analyze Objects at Run Time
Look at the contents of the data fields. It is easy to look at the contents of a specific field
of an object whose name and type are known when you write a program. But reflection lets you
look at fields of objects that were not known at compile time.
• f.set(obj, value) sets the field represented by f of the object obj to the new value.
• f.get(obj) returns an object whose value is the current value of the field of obj.
class A{
public int var1,var2;
A(int i, int j){
var1=i;
var2=j;
}
}
public class ConstructorDemo {
public static void main(String args[]) throws Exception{
A obj=new A(10,20);
System.out.println("Before n var1= "+obj.var1);
Field f1 = obj.getClass().getField("var1");
int v1 = f1.getInt(obj) + 1;
f1.setInt(obj, v1);
System.out.println("After n var1= "+v1);
System.out.println("Before n var2= "+obj.var2);
Field f2 = obj.getClass().getField("var2");
f2.set(obj,21);
System.out.println("After n var2= "+f2.get(obj));
}
}
Output:
Before var1= 10
After
var1= 11
Before var2= 20
After

var2= 21
Using Reflection to implement generic array manipulation code
The Array class in the java.lang.reflect package allows you to create arrays dynamically.
First the given array can be converted to an Object[] array. newInstance() method of Array class,
constructs a new array.
Object newarray= Array.newInstance(ComponentType, newlength)
newInstance() method needs two parameters
• Component Type of new array
To get component type
1. Get the class object using getClass() method.
2. Confirm that it is really an array using isArray().
3. Use getComponentType method of class Class, to find the right type for the array.
• Length of new array
Length is obtained by getLength() method. It returns the length of any array(method is
static method, Array.getLengh(array name)).
public class TestArrayRef {
static Object arrayGrow(Object a){
Class cl = a.getClass();
if (!cl.isArray()) return null;
Class componentType = cl.getComponentType();
int length = Array.getLength(a);
int newLength = length + 10;
Object newArray = Array.newInstance(componentType,newLength);
System.arraycopy(a, 0, newArray, 0, length);
return newArray;
}
public static void main(String args[]) throws Exception{
int arr[]=new int[10];
System.out.println(arr.length);
arr = (int[])arrayGrow(arr);
System.out.println(arr.length);
}
}
Output:
10
20
Object cloning

• A clone of an object is a new object that has the same state as the original but a different
identity. You can modify the clone without affecting the original.
When you make a copy of a variable, the original and the copy are references to the same object.
This means a change to either variable also affects the other.
If you want to make a clone of any class then the class must
 implement the Cloneable interface, and
 Redefine the clone method with the public access modifier.
import java.util.*;
class Test implements Cloneable{
int a=10;
public void display(){
System.out.println("a="+a);
}
public Object clone(){
try{
Test cloned = (Test)super.clone();
return cloned;
}
catch(CloneNotSupportedException e){
return null;
}
}
}
public class CloneDemo{
Test original=new Test();
original.a=20;
Test copy=(Test)original.clone();
copy.a=80;
original.display();
copy.display();
}
}
Output:
a=20
a=80
Proxy
Proxy used to create new classes at runtime that implement a given set of interfaces. The
proxy class can create brand-new classes at runtime.

The proxy class can create brand-new classes at runtime. Such a proxy class implements
the interfaces that you specify. In particular, the proxy class has the following methods:
• All methods required by the specified interfaces;
• All methods defined in the Object class (toString, equals, and so on).
To create a proxy object, you use the newProxyInstance method of the Proxy class. The method has
three parameters:
1. A class loader. As part of the Java security model, it is possible to use different
class loaders for system classes, classes that are downloaded from the Internet,
and so on.
2. An array of Class objects, one for each interface to be implemented.
3. An invocation handler.
Proxies can be used for many purposes, such as:
• Routing method calls to remote servers;
• Associating user interface events with actions in a running program;
• Tracing method calls for debugging purposes.

Unit III Event-Driven Programming
Graphics programming
Frame
Frame is a top-level window that has a title bar, menu bar, borders, and resizing corners. By
default, a frame has a size of 0 × 0 pixels and it is not visible.
Frames are examples of containers. It can contain other user interface components such as
buttons and text fields.
Class hierarchy for Frame
Java.awt
Component
Container
Window
Frame
Component & Window class Methods
java.awt.Component
• void setVisible(boolean b) - shows or hides the component depending on whether b is
true or false.
• void setSize(int width, int height) - resizes the component to the specified width and
height.
• void setBounds(int x, int y, int width, int height) - moves and resizes this component. The
location of the top-left corner is given by x and y, and the new size is given by the width
and height parameters.
• void setBackground(java.awt.Color) – set Background color to the window.
• void setForeground(java.awt.Color)- set Foreground color to the window.
• void repaint() - causes a repaint of the component ―as soon as possible.‖

java.awt.Window
• void setTitle(String s) - sets the text in the title bar for the frame to the string s.
Frame’s constructors:
Frame( ) - creates a standard window that does not contain a title.
Frame(String title) - creates a window with the title specified by title
Methods of Frame class:
• void setSize(int newWidth, int newHeight) - method is used to set the dimensions of the
window. The dimensions are specified in terms of pixels.
• void setVisible(boolean visibleFlag)- The component is visible if the argument to this
method is true. Otherwise, it is hidden.
• void setTitle(String newTitle)- change the title in a frame window.
Creating a Frame Window
Method 1: In main() method
 Create an instance of a Frame class.
Frame f=new Frame(―frame name );‖
 Set the frame size
f.setSize(500,500);
 Make the frame visible
f.setVisible(true);
Example:
The following java program creates a frame with the dimension as 600 x 400 and makes it
visible in the screen. Import java.awt package because Frame class is available in that package.
import java.awt.*;
public class Demo{
Frame f=new Frame("Demo");
f.setSize(600,400);
f.setVisible(true);
}
}
Out Put:

Method :2
• Create a subclass of Frame.
• In the Subclass constructor
 Change the frame title by calling superclass [Frame] constructor using super(String)
method call.
 Set the size of the window explicitly by calling the setSize( ) method.
 Make the frame visible by calling setVisible() method.
• In main() method
 Create an instance of subclass.
Example:
The following java program creates a frame with the dimension as 600 x 400 and makes it
visible in the screen. Import java.awt package because Frame class is available in that package.
import java.awt.*;
public class Demo extends Frame{
Demo(String s){
super(s);
setSize(600,400);
setVisible(true);
}
Out Put:
}
Demo ob=new Demo("Demo");
}
Working with 2D shapes
Graphics: java.awt.Graphics
The Graphics class is part of the java.awt package. The Graphics class defines a number of
drawing functions. Each shape can be drawn edge-only or filled. Objects are drawn and filled in
the currently selected graphics color, which is black by default. When a graphics object is drawn
that exceeds the dimensions of the window, output is automatically clipped.
Java Coordinate System
Java’s coordinate system has the origin (0, 0) in the top left corner. Positive x values are to the

right, and positive y values are down. Coordinate units are measured in pixels (picture element).
All pixel values are integers; there are no partial or fractional pixels.
X coordinate: Horizontal distance moving right from the left of the screen.
Y coordinate: Vertical distance moving from top to bottom of the screen.
The Graphics class provides a set of simple built-in graphics primitives for drawing, including
lines, rectangles, polygons, ovals, and arcs.
Lines
To draw straight lines, use the drawLine method. drawLine takes four arguments: the x and y
coordinates of the starting point and the x and y coordinates of the ending point.
• void drawLine(int startX, int startY, int endX, int endY) - displays a line in the current
drawing color that begins at startX,startY and ends at endX,endY.
Example: Demo.java
import java.awt.*;
Demo(String s){
super(s);
setSize(100,100);
setVisible(true);
}
public void paint(Graphics g) {
g.drawLine(10,10,60,60);
}
Demo ob=new Demo("Line Demo");
}
}

Output:

Rectangles
The Java graphics primitives provide two kinds of rectangles: Plain rectangles and Rounded
rectangles(which are rectangles with rounded corners).
• void drawRect(int x, int y, int width, int height)
• void fillRect(int x, int y, int width, int height)
• void drawRoundRect(int x, int y, int width, int height, int xDiam, int yDiam)
• void fillRoundRect(int x, int y, int width, int height, int xDiam, int yDiam)
A rounded rectangle has rounded corners. The upper-left corner of the rectangle is at x, y. The
dimensions of the rectangle are specified by width and height. The diameter of the rounding arc
along the X axis is specified by xDiam. The diameter of the rounding arc along the Y axis is
specified by yDiam.
Example: Demo.java
import java.awt.*; Demo ob=new Demo("Line Demo");
Demo(String s){
super(s);
setSize(500,500);
setVisible(true);
}
g.drawRect(100,100,60,60);
g.fillRect(250,100,60,60);
g.drawRoundRect(100,250,60,60,10,10);
g.fillRoundRect(250,250,60,60,20,20);
}
}
}
Output:

Polygons
Polygons are shapes with an unlimited number of sides. Set of x and y coordinates are needed to
draw a polygon, and the drawing method starts at one, draws a line to the second, then a line to
the third, and so on.
• void drawPolygon(int x[ ], int y[ ], int numPoints)
• void fillPolygon(int x[ ], int y[ ], int numPoints)
x[]- An array of integers representing x coordinates
y[]- An array of integers representing y coordinates
numPoints- An integer for the total number of points
Example: Demo.java
import java.awt.*;
int x1[] = { 39,94,97,112,53,58,26 };
int y1[] = { 133,174,136,170,208,180,206 };
g.drawPolygon(x1,y1,7);
int x2[] = { 139,194,197,212,153,158,126 };
int y2[] = { 133,174,136,170,208,180,206 };
g.fillPolygon(x2,y2,7);
}
Demo ob=new Demo("Polygon Demo");
}
}
Output:

Ovals
Use ovals to draw ellipses or circles.
• void drawOval(int top, int left, int width, int height)
• void fillOval(int top, int left, int width, int height)

Example:Demo.java
import java.awt.*;
}
}
Demo(String s){
super(s);
setSize(300,300);
setVisible(true);
}
g.drawOval(20,120,70,70);
g.fillOval(140,120,100,70);
}
Demo ob=new Demo("Oval Demo");
Arc
The arc is drawn from startAngle through the angular distance specified by arkAngle. Angles are
specified in degrees. The arc is drawn counterclockwise if sweepAngle is positive, and clockwise
if arkAngle is negative.
• void drawArc(int x, int y, int width, int height, int startAngle, int arcAngle)
• void fillArc(int x, int y, int width, int height, int startAngle, int arcAngle)
x=0
y=0
width=100
height=100
Startangle=90
arcAngle=180

Example:Demo.java
import java.awt.*;
Demo(String s){
super(s);
setSize(300,300);
setVisible(true);
}
}
Output:
}
g.drawArc(20,120,90,90,90,180);
g.fillArc(120,120,90,90,90,180);
g.drawArc(170,120,90,90,90,-180);
}
Demo ob=new Demo("Arc Demo");
Drawing Text
Draw text on the screen using the method drawstring().
• void drawstring(String text, int x, int y)- draws a string in the current font and color.
import java.awt.*;
Demo(String s){
super(s);
setSize(200,200);
setVisible(true);
}
g.drawString("welcome", 75, 100);
}
Demo ob=new Demo("Text Demo");
}
}

Using color, fonts, and images
Color: java.awt.Color
Color class creates a solid RGB color with the specified red, green, blue value in the range (0-
255). Java’s abstract color model uses 24-bit color. The values of each color must be in the range
(0- 255).
Constructor:
Color(int red, int green, int blue) - create new color object for any combination of red, green,
and blue.
Java.awt.Color class used to create new color object for any combination of red, green, and blue,
and it predefines a few color constants. They are stored in class variables,
Color.white (255,255,255)
Color.black (0,0,0)
Color.lightGray (192,192,192)
Color.gray (128,128,128)
Color.darkGray (64,64,64)
Color.red (255,0,0)
Color.blue (0,0,255)
Color.yellow (255,255,0)
Color.magenta (255,0,255)
Color.cyan( 0,255,255)
Color.pink (255,175,175)
Color.orange (255,200,0)
Color.green(0,255,0)
java.awt.Component
Component class defines setBackground() and setForeground() methods for setting background
and foreground colors to the window. Since Frame is a subclass of Component class it can use
these methods.
• void setBackground(java.awt.Color) – set Background color to the window.
• void setForeground(java.awt.Color)- set Foreground color to the window.
java.awt.Graphics
setColor() method used to set the current color for the graphics context which is defined in
Graphics class.
• void setColor(java.awt.Color)

Example: The following program for designing a frame with square boxes, each of which has a
randomly chosen color in it.
Demo ob=new Demo("Color Demo");
import java.awt.*;
Demo(String s){
}
}
Output:
super(s);setSize(200,200);setVisible(true);
setBackground(Color.black);
}
int rval, gval, bval;
for (int j = 30; j < 200-30; j += 30)
for (int i = 30; i < 200-30; i+= 30){
rval = (int)Math.floor(Math.random() * 256);
gval = (int)Math.floor(Math.random() * 256);
bval = (int)Math.floor(Math.random() * 256);
g.setColor(new Color(rval,gval,bval));
g.fillRect(i,j,25,25);
}
}
Font: java.awt.Font
Font class is used to create Font Objects to set the font for drawing text, labels, textField, buttons
etc..,
One Font constructor has this general form:
Font(String fontName, int fontStyle, int pointSize)
Here, fontName specifies the name of the desired font. The style of the font is specified by
fontStyle. It may consist of one or more of thesethree constants: Font.PLAIN, Font.BOLD, and
Font.ITALIC. The size, in points, of the font is specified by pointSize. point size may or may
not be the height of the characters.
To draw characters in a font, first create an object of the class Font. then specify the font name,
the font style, and the point size.

Methods
Java.awt.Graphics
• void setFont(Font fontObj)- selects a font for the graphics context. That font will be used
for subsequent text drawing operations.
• Font getFont( )- get the current font by calling getFont( ).
Java.awt.Component
• void setFont(Font fontObj)
Example: The following program that draws several lines of text in different fonts.
import java.awt.*;
Demo(String s){
}
Font f = new Font("TimesRoman", Font.PLAIN, 18);
Font fb = new Font("TimesRoman", Font.BOLD, 18);
Font fi = new Font("TimesRoman", Font.ITALIC, 18);
Font fbi = new Font("TimesRoman", Font.BOLD + Font.ITALIC, 18);
g.setFont(f);
g.drawString("This is a plain font", 10, 50);
g.setFont(fb);
g.drawString("This is a bold font", 10, 75);
g.setFont(fi);
g.drawString("This is an italic font", 10, 100);
g.setFont(fbi);
g.drawString("This is a bold italic font", 10, 125);
Demo ob=new Demo("Font Demo");
}
}
Output:
}
Image: java.awt.Image
Image class provides support for displaying and manipulation of graphical images. Image is
simply a rectangular graphical object.

Java provides the functions for reading images that are stored in local files and display them on
graphics object.
Step1: Loading an image
java.awt.Toolkit
• Toolkit getDefaultToolkit()- returns the default toolkit.
• Image getImage(String filename) - returns an image that will read its pixel data from a
file.
Toolkit object can only read GIF and JPEG files.
Step2: displaying an image
java.awt.Graphics
• boolean drawImage(Image img, int x, int y, ImageObserver observer)- draws a scaled image.
• boolean drawImage(Image img, int x, int y, int width, int height, ImageObserver observer) -
draws a scaled image. The system scales the image to fit into a region with the given width
and height. Note: This call may return before the image is drawn.
Example: the following program draws a tiled graphics image from the top-left corner to bottom
right corner of the window.
import java.awt.*;
Demo(String s){
}
Toolkit tk = Toolkit.getDefaultToolkit();
Image img= tk.getImage("E:/Sample/ball.jpg");
for (int i = 20; i <300-20; i=i+20)
for (int j = 40; j <300-20; j=j+20)
g.drawImage(img,i,j,20,20,null);
}
Demo ob=new Demo("Image Demo");
}
}
Output:

Component Constructor Methods
Label Label( )
Label(String str)
Label(String str, int how)
void setText(String str)
String getText( )
Button Button( )
Button(String str)
void setLabel(String str)
String getLabel( )
List List( )
List(int numRows)
List(int numRows, boolean multipleSelect)
void add(String name)
void add(String name, int
index)
String getSelectedItem( )
int getSelectedIndex( )
String[ ] getSelectedItems( )
Choice Choice( ) void add(String name)
String getSelectedItem( )
int getSelectedIndex( )
Checkbox Checkbox( )
Checkbox(String str)
Checkbox(String str, boolean on)
Checkbox(String str, boolean on, CheckboxGroup cbGroup)
Checkbox(String str, CheckboxGroup cbGroup, boolean on)
boolean getState( )
void setState(boolean on)
String getLabel( )
void setLabel(String str)
TextField TextField( )
TextField(int numChars)
TextField(String str)
TextField(String str, int numChars)
String getText( )
void setText(String str)
void setEditable(boolean
canEdit)
TextArea TextArea( )
TextArea(int numLines, int numChars)
TextArea(String str)
TextArea(String str, int numLines, int numChars)
void append(String str)
void insert(String str, int
index)

AWT Components
• All components are subclass of Component class
• Components allow the user to interact with application. A layout manager
arranges components within a container (Frame/Applet/Panel).
Adding and Removing Controls
• add(Component compObj)- add components to the conatainer. Once it is added, it will
automatically be visible whenever its parent window is displayed. Here, compObj is an
instance of the control that you want to add.
• void remove(Component obj)- remove a control from a window

Scrollbars Scrollbar( )
Scrollbar(int style)
Scrollbar(int style, int initialValue, int thumbSize, int min, int max)
int getMinimum( )
int getMaximum( )
void setValues(int
initialValue, int thumbSize,
int min, int max)
Label
• Labels are components that hold text.
• Labels don’t react to user input. It is used to identify components.
Constructors
• Label(String str) - constructs a label with left-aligned text.
• Label(String str, int how) - constructs a label with the alignment specified by how.
Methods
• void setText(String str)- set the text in the label
• String getText( )- return the text of label
Example: The following example creates three labels and adds them to a frame..The labels are
organized in the frame by the flow layout manager.
import java.awt.*; Demo ob=new Demo("Label Demo");
Label lb1 = new Label("One");
Label lb2 = new Label("Two");
Label lb3 = new Label("Three");
FlowLayout flow= new FlowLayout();
Demo(String s){
super(s);
setSize(200,200);
setLayout(flow);
add(lb1);add(lb2);add(lb3);
setVisible(true);
}

}
}
Output:

Button
A push button is a component that contains a label and that generates an event when it is pressed.
Push buttons are objects of type Button.
Constructors
• Button( )- creates an empty button
• Button(String str)- creates a button that contains str as a label.
Methods
• void setLabel(String str) -set the label in the button
• String getLabel( ) -return the label of button
Example: The following example creates three buttons and adds them to a frame. The buttons
are organized in the frame by the flow layout manager.
import java.awt.*; Demo ob=new Demo("Button Demo");
}}
Output:
Button b=new Button();
Button b1=new Button();
Button b2=new Button("Button 2");
Demo(String s){
super(s);setSize(200,200);
setLayout(flow);
b1.setLabel("Button 1");
add(b);add(b1);add(b2);
setVisible(true);
}
List
The List class provides a compact, multiple-choice, scrolling selection list. List object can be
constructed to display any number of choices in the visible window. It allows the user to select
multiple items.
Constructors
• List( )- allows to select one item at any one time
• List(int numRows)- the value of numRows specifies the number of entries in the list that

will be visible always
• List(int numRows, boolean multipleSelect)- if multipleSelect is true, then the user may
select two or more items at a time
Method
• void add(String name)- Here, name is the name of the item added to the list. The first
form adds items to the end of the list.
• void add(String name, int index) -adds the item at the index specified by index
• String getSelectedItem( )- return the selected item
• String[ ] getSelectedItems( )- return the selected items.
Example: The following example creates a list and adds it to a frame.
import java.awt.*;
List l1=new List(2);
List l2=new List(3);
List l3=new List(4,true);
Label lb1 = new Label("Dept");
Demo(String s){
super(s);
setSize(200,300);
setLayout(flow);
l1.add("CSE");l1.add("ECE");l1.add("EEE");l1.add("MECH");
add(lb1);add(l1);add(lb2);add(l2);add(lb3);add(l3);
setVisible(true);
}
Demo ob=new
Demo("List Demo");
}
}

CheckBox
A check box is a control that is used to turn an option on or off. It consists of a small box that can
either contain a check mark or not. There is a label associated with each check box that describes
what option the box represents.
Constructors
• Checkbox( )- check box whose label is initially blank
• Checkbox(String str)- check box whose label is specified by str.
• Checkbox(String str, boolean on) - allows you to set the initial state of the check box. If
on is true, the check box is initially checked
• Checkbox(String str, boolean on, CheckboxGroup cbGroup)- group is specified by
cbGroup
• Checkbox(String str, CheckboxGroup cbGroup, boolean on)
Methods
• boolean getState( )
• void setState(boolean on)
• String getLabel( )
• void setLabel(String str)
CheckboxGroup
Create a set of mutually exclusive check boxes in which one and only one check box in the group
can be checked at any one time. These check boxes are often called radio buttons. The default
constructor is defined, which creates an empty group.
Example: The following example creates a checkbox group (Gender) and checkboxes
(Languages Known).
import java.awt.*;
Label l1=new Label("Gender");
Label l2=new Label("Languages Known");
CheckboxGroup cg=new CheckboxGroup();
Checkbox c1=new Checkbox("Male",cg,true);
Checkbox c2=new Checkbox("Female",cg,false);

Checkbox c3=new Checkbox("VisualBasic");
Checkbox c4=new Checkbox("C++");
Checkbox c5=new Checkbox("Java");
Checkbox c6=new Checkbox("C");
}
}
Output:
Demo(String s){
super(s);
setSize(200,200);
setLayout(flow);
add(l1);add(c1);add(c2);
add(l2);add(c3);add(c4);add(c5);add(c6);
setVisible(true);
}
Demo ob=new Demo("Checkbox Demo");
Choice
The Choice class is used to create a pop-up list of items from which the user may choose. It
allows the user to select single item at any time. Choice only defines the default constructor,
which creates an empty list.
To add a item to the list, call add( ). It has this general form:
• void add(String name)
• To determine which item is currently selected, you may call either getSelectedItem( ) or
getSelectedIndex( ).
import java.awt.*;
Label lb=new Label("City");
Choice c=new Choice();
Demo(String s){
super(s);
setSize(200,200);setLayout(flow);
c.add("Chennai");c.add("Coimbatore");
c.add("KanyaKumari");c.add("Madurai");
c.add("Tirunelveli");
add(lb);add(c);
setVisible(true);
}
Demo ob=new Demo("Checkbox Demo");
}
}

TextField
Text fields allow the user to enter strings and to edit the text using the arrow keys, cut and paste
keys, and mouse selections.
• TextField( )- creates a default text field
• TextField(int numChars)- creates a text field that is numChars characters wide
• TextField(String str)- initializes the text field with the string contained in str
• TextField(String str, int numChars)
Methods
• String getText( )
• void setText(String str)
TextArea
Simple multiline editor allow the user to enter strings.
TextArea and TextField are subclass of TextComponent. Therefore, it supports the getText( ),
setText( ), getSelectedText( ), select( ), isEditable( ), and setEditable( ) methods described in
TextField class.
import java.awt.*;
Label lb1=new Label("Name");
Label lb2=new Label("No");
Label lb3=new Label("Message");
TextField t1=new TextField(20);
TextField t2=new TextField(15);

TextArea ta=new TextArea(2,10);
Demo(String s){
super(s);
setSize(250,200);
setLayout(flow);
add(lb1);add(t1);
add(lb2);add(t2);
add(lb3);add(ta);

setVisible(true);
}
Demo ob=new Demo("TextComponents Demo");
}
}
output:

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