B.Sc. III(VI Sem) Advance Java Unit3: AWT & Event Handling

1
B.Sc. III (VI Sem)
Advance Java Programming (Unit-III)
Prepared by,
Mr. Hushare Y.V., [M.Sc., MCA, SET], Asst. Professor
UNIT-III: AWT & Event Handling
* Introduction to AWT *
 AWT stands for Abstract Window Toolkit. It is provided in java as a java
package i.e. ‘java.awt”
 The ‘java.awt’ contains numerous classes and methods that allow us to create
and manage window applications.
 This AWT package allows a programmer to Create a standard window, dialog
box, controls, etc.
 In windows, controls are nothing but window element that allow user to
interact with your application. For example, Command Button, Scroll Bar,
Menu Bar, etc.
 The following figure shows the AWT class hierarchy:
 Component:
o Component is an abstract class; it contains attributes of visual components.
o All user interface elements like button, label, checkbox, scrollbar etc. are
displayed on the screen are subclasses of class Component.
Object
Container
Panel
Applet
Wndow
Frame
Dialog
Label Button Checkbox Scrollbar TextComponent
TextField TextArea
Component
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B.Sc. III (VI Sem)
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 Container:
o Container is a class that defined positioning of controls i.e. layout within
the window that we perform in .Net just by drag and drop.
 Panel:
o This class is used to create panel window, the window not having border,
title bar, and menu bar. Ex. Applet window
 Frame:
o This class is used to create a standard window i.e. having border, title bar
and menu bar.
 The ‘java.awt’ is one of the java’s largest package.
 The following table shows few of the classes defined in ‘java.awt’ package.
# Class name Description
1 Frame
Creates a standard window that has t title bar, resize
corners, and a menu bar.
2 Label Creates a label that displays a string.
3 Button Creates a push button control.
4 Checkbox Creates a checkbox control.
5 TextField Creates a single-line edit control.
6 TextArea Creates a multiline edit control.
7 List Creates a list from which the user can choose..
8 Scrollbar Creates a scroll bar control.
9 BorderLayout
The border layout manager. Border supports five
positions on window at which we can place control:
North, South, East West, and Center.
10 CardLayout
The card layout manager. Card layouts emulate
index cards. Only the one on top is showing.
11 FlowLayout
The flow layout manager. Flow layout positions
components left to right, top to bottom.
12 GridLayout
The grid layout manager. Grid layout displays
components in a two-dimensional grid.

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* Working with Frame Window *
 A frame is thought of as a “window”.
 To create a frame window, we have to follow TWO steps:
1. By extending ‘Frame’ class.
2. By creating object of ‘Frame’ class.
1. Creating frame window by extending ‘Frame’ class:
2. Creating frame window By creating object of ‘Frame’ class:
import java.awt.*;
class MYWINDOW extends Frame
{
MYWINDOW()
{
setSize(500,400);
setTitle(“My First frame window”)
setVisible(true);
setLayout(null); // No layout manager(Default: Border Layout
}
public static void main(String args[])
{
MYWINDOW obj= new MYWINDOW();
}
}
import java.awt.*;
class MYWINDOW
{
{
Frame obj=new Frame();
obj.setSize(500,400);
obj.setTitle(“My First frame window”)
obj.setVisible(true);
obj.setLayout(null); // No layout manager(Default: Border Layout
}
}
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B.Sc. III (VI Sem)
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 The output of the above both programs is same as shown below:
* Label Control *
 A label is window element that contains a string, which it displays.
 The class ‘Label’ defines the following THREE constructors used to create
label control:
1. Label() : This constructor creates a blank label.
2. Label(String str): This constructor creates a label that contains a string
‘str’. This string is Left-justified.
3. Label(String str, int how) :This constructor creates a label that contains
a string ‘str’ using alignment ‘how’. The value of ‘how’ must be
one of these constants: Label.LEFT, Label.RIGHT or Label.CENTER.

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B.Sc. III (VI Sem)
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 For example,
 The output of the above program is as follows:
import java.awt.*;
class LABEL
{
{
obj.setLayout(null);
obj.setTitle("Program on Label control");
Label x=new Label("Enter First Name:");
x.setBounds(40,40,200,30);
Label y=new Label("Enter Last Name:", Label.RIGHT);
y.setBounds(40,80,200,20);
obj.add(x);
obj.add(y);
}
}
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* Button Control *
 A command button is a component that has a label printed over it and
generates an event when it is pressed.
 The class ‘Button’ defines the following TWO constructors used to create
button control:
Constructor
Prototype
Purpose
Button (); It creates a blank button.
Button (String str);
It creates a button that contains a string ‘str’ as
button label.
For example,
import java.awt.*;
class BUTTON
{
{
obj.setLayout(null);
obj.setTitle("Program on Button control");
Button B1=new Button();
B1.setBounds(40,40,100,20);
B1.setLabel("OK");
Button B2=new Button("CANCEL");
B2.setBounds(40,70,100,20);
obj.add(B1);
obj.add(B2);
}
}

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 The output of above program is as follows:
* Checkbox Control *
 A check box is a component that allow user to select the option. By default
they are in square box shape.
 A check box control has ‘label’ and ‘state’ these two attributes.
 The state of check box is either ‘checked’ or ‘unchecked’.
 The class ‘Checkbox’ is defined in ‘java.awt’ package with following
THREE types of constructors to create check boxes.
Constructor Purpose
Checkbox() It creates a check box with blank label.
Checkbox(String str) It creates a check box whose label is specified by string ‘str’.
Checkbox(String str,
boolean X)
It creates a check box with label ‘str’ and also allow to set
initial state i.e. true or false.
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B.Sc. III (VI Sem)
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For example,
The output of above program is:
NOTE: Here we used layout manager ‘FlowLayout’. So no need to set bounds
for control that we are positioning within window.
import java.awt.*;
class CHECKBOX
{
{
obj.setLayout(new FlowLayout());
obj.setTitle("Program on Checkbox control");
Checkbox c1,c2,c3;
c1=new Checkbox();
c2=new Checkbox("Marks Memo");
c3=new Checkbox("TC",true);
obj.add(c2); obj.add(c3); obj.add(c1);
}
}

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* Text field Control *
 A text field is a single line component that allow user to enter strings and to
edit the string present in it.
 The class ‘TextField’ defines the following FOUR constructors used to create
text field control:
Constructor Purpose
TextField() It creates a blank field of default width of 2 characters.
TextField(int n) It creates a text field which is ‘n’ characters wide.
TextField(String str) It creates a text field and initializes a string ‘str’ to it.
TextField(String str,
int n)
It creates a text field and initializes a string ‘str’ to it and sets
its width to ‘n’ characters.
For example,
import java.awt.*;
class TEXTFIELD
{
{
obj.setTitle("Program on text field control");
TextField text1,text2;
text1=new TextField();
text1.setText("Hello India");
text1.setEditable(false);
text2=new TextField("Hello World");
obj.add(text1);
obj.add(text2);
}
}
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* Text area Control *
 A text area is a component that allow user to enter multiple line of text and to
edit.
 The class ‘TextArea’ defines the following FIVE constructors used to create
text area control:
Constructor Purpose
TextArea() It creates a default text area control.
TextArea(int x, int y) It creates a text area control of ‘x’ number of lines and of
width ‘y’ characters.
TextArea(String str) It creates a text area and initializes string ‘str’ to it.
TextArea(String str, int x,
int y)
It creates a text area of ‘x’ lines, of width ‘y’ character
and initializes string ‘str’ to it.
TextArea(String str, int x,
int y, int sBars)
It creates a text area of ‘x’ lines, of width ‘y’ character
and initializes string ‘str’to it having scroll bars specified
by ‘sBars’.

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For example,
import java.awt.*;
class TEXTAREA
{
{
obj.setTitle("Program on text area control");
TextArea TA1,TA2,TA3;
TA1=new TextArea();
TA2=new TextArea("Hello Indian Hello
World",10,4,TextArea.SCROLLBARS_BOTH);
TA3=new TextArea(5,10);
obj.add(TA1);
obj.add(TA2);
obj.add(TA3);
}
}
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* List Control *
 The class ‘List’ provides following THREE constructors to create list control.
 By default multi-selection property of list control is FALSE.
Constructor Purpose
List() It creates a list control that allows only one item to be selected
at a time with default FOUR rows.
List( int numRows) It create a list control and integer ‘numRows’ is number of
items in the list that will always be visible.
List(int numRows,
boolean flag)
It creates a list control in which multiple selections are allowed
or not is specified by ‘flag’ i.e. boolean value ‘true’ or ‘false’.
For example,
import java.awt.*;
class LIST
{
{
obj.setTitle("Program on list control");
List x=new List(); //List X
x.add("Udgir");
x.add("Latur");
List y=new List(1); // List Y
y.add("Amravati");
y.add("Latur");
y.add("Banglore");
List z=new List(5,true); // List Z
z.add("Udgir");
z.add("Amravati");
z.add("Banglore");
obj.add(x); obj.add(y); obj.add(z);
}
}

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* Scrollbar Control *
 A scrollbar control is used to view the contents of the page which can’t be
displayed on screen in one page.
 Two types of scrollbars are available i.e. Horizontal and Vertical.
 Each scroll bar is assigned with a range of values i.e. ‘Minvalue’ and
‘Maxvalue’(Integers).
 A scrollbar consists of several individual parts: Arrows on each end and a
slider box(Thumb).
 The position of slider box on the scrollbar indicates the current value of the
scrollbar.
 The class ‘Scrollbar’ provides following THREE constructors to create
scrollbar.
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Constructor Purpose
Scrollbar() It creates a default vertical scrollbar.
Scrollbar(int style) It creates either vertical OR horizontal scrollbar. The
‘style’ can take one of the TWO values
Scrollbar.VERTICAL(0) or Scrollbar.HORIZONTAL(1)
Scrollbar(int style,
int initial,
int thumbSize,
int min,
int max)
It creates scrollbar with specified initial value. It also
allow to specify Minvalue and Maxvalue. The
‘thumbSize’ determines the width of the slider box.
For example,
import java.awt.*;
class SCROLLBAR
{
{
obj.setTitle("Program on scrollbar control");
Scrollbar x=new Scrollbar();
Scrollbar y=new Scrollbar(Scrollbar.HORIZONTAL);
Scrollbar z=new Scrollbar(Scrollbar.HORIZONTAL,500,500,0,1000);
z.setPreferredSize(new Dimension(200,200)); //Dimension(width,height)
y.setPreferredSize(new Dimension(100,200)); //Dimension(width,height)
obj.add(x);
obj.add(y);
obj.add(z);
}
}

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B.Sc. III (VI Sem)
Prepared by,
* Layout Manager *
 Layout means the arrangement of components within the container.
 In java, container is nothing but a window.
 Positioning controls within the window is handled in java by some classes
defined, called Layout Managers.
 In java, the following FIVE classes represents different layout managers:
1. java.awt.BorderLayout
2. java.awt.GridLayout
3. java.awt.FlowLayout
4. java.awt.CardLayout
5. java.awt.GridBagLayout
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B.Sc. III (VI Sem)
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* BorderLayout Manager *
 This layout is used to arrange the components in FIVE regions: north, south,
east, west and center. Each region(area) may contain only one component.
 It is default layout for frame(standard) window.
 The BorderLayout class contains following five defined constant’s:
o public static final int NORTH
o public static final int SOUTH
o public static final int EAST
o public static final int WEST
o public static final int CENTER (Default)
 For example,
The output of above program is as follows:
import java.awt.*;
class BORDERLAYOUT
{
{
obj.setTitle("Program on list control");
BorderLayout mgr=new BorderLayout();
obj.setLayout(mgr);
Button b1=new Button("Hello");
Button b2=new Button("World");
Button b3=new Button("Thank you!");
obj.add(b1,BorderLayout.WEST);
obj.add(b2,BorderLayout.NORTH);
obj.add(b3); // Default CENTER
}
}

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B.Sc. III (VI Sem)
Prepared by,
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B.Sc. III (VI Sem)
Prepared by,
* GridLayout Manager *
 The grid layout divides the window into rows and columns.
 Each cell is referred as a single Grid.
 One component is displayed in one grid of the window.
 For example,
import java.awt.*;
class GRIDLAYOUT
{
{
obj.setTitle("Program on Grid layout manager");
GridLayout mgr=new GridLayout(2,2);
obj.setLayout(mgr);
Button b1=new Button("1");
obj.add(b1); obj.add(b2);
obj.add(b3); obj.add(b4);
}
}

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B.Sc. III (VI Sem)
Prepared by,
* FlowLayout Manager *
 The flow layout is used to arrange the components in a line one after another(in
a flow).
 It is default layout manager for panel(applet) window.
 This layout manager support THREE alignments by defining following
integer constants in ‘FlowLayout’ class:
 public static fine int LEFT
 public static fine int RIGHT
 public static fine int CENTER(Default)
 For example,
import java.awt.*;
class FLOWLAYOUT
{
{
obj.setTitle("Program on flow layout manager");
FlowLayout mgr=new FlowLayout(FlowLayout.RIGHT);
obj.setLayout(mgr);
obj.add(b1);
obj.add(b2);
obj.add(b3);
obj.add(b4);
}
}
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* CardLayout Manager *
 This layout manager is different among all other layout managers.
 This layout manager defines a container and allow to add any number of
panel windows containing group of components, but only one panel
window can be shown at a given time.
 The panel window is referred as a card.
 Only one card is shown at a time and other present but hidden below it.
 For example,
import java.awt.*;
class CARDLAYOUT
{
{
obj.setTitle("Program on card layout manager");
CardLayout mgr=new CardLayout();
obj.setLayout(mgr);
Panel cricket=new Panel(); //Creating card for CRICKET
cricket.add(new Checkbox("Jaques Kallis"));
cricket.add(new Checkbox("Virat Kohli"));
Panel tennis=new Panel(); // Creating card for TENNIS
tennis.add(new Checkbox("Pit Sampras"));
tennis.add(new Checkbox("John Edberg"));
obj.add(cricket,"X"); // Adding group(card) to container
obj.add("Y",tennis); // Addign group(card) to container
mgr.show(obj,"Y");
}
}
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* CardLayout Manager *
 This layout manager is different among all other layout managers.
 This layout manager defines a container and allow to add any number of
panel windows containing group of components, but only one panel
window can be shown at a given time.
 The panel window is referred as a card.
 Only one card is shown at a time and other present but hidden below it.

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 For example,
import java.awt.*;
class CARDLAYOUT
{
{
obj.setTitle("Program on card layout manager");
CardLayout mgr=new CardLayout();
obj.setLayout(mgr);
Panel cricket=new Panel(); //Creating card for CRICKET
cricket.add(new Checkbox("Jaques Kallis"));
cricket.add(new Checkbox("Virat Kohli"));
Panel tennis=new Panel(); // Creating card for TENNIS
tennis.add(new Checkbox("Pit Sampras"));
tennis.add(new Checkbox("John Edberg"));
obj.add(cricket,"X"); // Adding group(card) to container
obj.add("Y",tennis); // Addign group(card) to container
mgr.show(obj,"Y");
}
}
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* Event Delegation Model *
 Event Delegation model is mechanism used to perform event handling in Java.
 The principles of event delegation model are:
1. A source(component) generates an event and sends it to one or more
listeners.
2. The listeners simply waits until it receives an event. Once received, the
listener processes the event and then returns.
NOTE : Listeners must be registered with a source.
1. Event :
 An event is an object of event class that describes a state change in a source.
 For example, Event may be generated when button is pressed, item in a list
is selected or mouse is clicked.
2. Source :
 A source is an object of control (e.g. Label, Button, etc.) that generates an
event.
 A single source may generate more than one type of events.
 A source must be registered with listeners. The general form of registration
is:

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Here, ‘add’ and ‘Listener’ are keywords. A ‘Type’ is name of the event. The ‘el’
is reference to event listener.
For example,
Button b1=new Button();
b1.addActionListener(this);
When button ‘b1’ is pressed, notification to listener will be sent.
3. Listener :
 A listener is an object that is notified when an event occurs. It has TWO major
requirements:
1. It must have been registered with one or more sources to receive
notifications about specific event types.
2. It must be implemented to receive and process these notifications.
 The methods that can receive and process the events are defined in built-in
interfaces.
 A single interface has one or more methods declared in it.
 For example, ActionListener interface has only one method i.e.
ActionPerformed() method but MouseListener interface has multiple
methods for different event that mouse can generate.
public void addTypeListener(TypeListener el);
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* Java AWT Events *
 Here we will discuss various events that we can handle by using event
delegation model in java.
 The following table shows various events and corresponding classes defined
in ‘java.awt.event’ package whose object is automatically generated when
event occurs.
Event
Event Class whose object is
generated
Window activated
WindowEvent
Window closed
Window is being closed
Window is deactivated
Window is de-iconified
Window is iconified
Window is opened
Button pressed ActionEvent
Adjustment using scrollbar AdjustmentEvent
Control gets focus
FocusEvent
Control loses focus
State of control changed(checkbox) ItemEvent
Change occurs in text field or text area TextEvent
Mouse button is pressed and released at a time
MouseEvent
Mouse pointer enters into control
Mouse pointer leaves control
Mouse Button is pressed
Mouse Button is released
Mouse dragged
MouseMotionEvent
Mouse moved

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* Sources of Event *
 Source of the event is the component/control (like, button, checkbox, etc) on
which event is occurring.
 Particularly, in a java program an object of component/control is a source of
an event.
 The following table shows the various event and possible sources of the event.
Event Sources of Event
Window activated
A panel or frame window
Window closed
Window is being closed
Window is deactivated
Window is de-iconified
Window is iconified
Window is opened
Button pressed A Button
Adjustment using scrollbar Scrollbar
Control gets focus
Any Control
Control loses focus
State of control changed(checkbox) Checkbox, radio button
Change occurs in text field or text area Text field or Text area
Mouse button is pressed and released at a time
Any Control
Mouse pointer enters into control
Mouse pointer leaves control
Mouse Button is pressed
Mouse Button is released
Mouse dragged
Input device mouse
Mouse moved
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* Event Listener Interface *
In java number of interfaces defined that contain methods to handle the generated
events. Hence these interfaces are also called event handlers.
For each event class there is its corresponding listener interface is defined in
“java.awt.event” package.
The following table shows event class and associated listener interface names.
Event Class Listener Interface
WindowEvent WindowListener
MouseEvent MouseListener
MouseMotionEvent MouseMotionListener
FocusEvent FocusListener
ActionEvent ActionListener
AdjustmentEvent AdjustmentListener
ItemEvent ItemListener
TextEvent TextListener
 A single listener interface defined with one or more abstract methods to handle
different events as described below:
Abstract methods declared in interface WindowListener
Method Purpose
windowActivated() invoked when a window is activated.
windowDeactivated() Invoked when window is deactivated
windowClosing() Invoked when window is being closed.
windowOpened() Invoked when window is get opened.
windowIconified() Invoked when window is iconified.
windowDeiconified() Invoked when window is de-iconified.
windowClosed() Invoked when widow is closed.

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Abstract methods declared in interface MouseListener
Method Purpose
mouseCliked() Invoked when mouse is pressed and released at a same time
mousePressed() Invoked when mouse button is pressed.
mouseReleased() Invoked when mouse button is released.
mouseEntered() Invoked when mouse pointer enters into control.
moueseExited() Invoked when mouse pointer leaved control.
Abstract methods declared in interface MouseMotionListener
Method Purpose
mouseDragged() Invokes multiple times as the mouse is dragged.
mouseMoved() Invokes multiple times as the mouse is moved.
Abstract methods declared in interface FocusListener
Method Purpose
focusGained() Invoked when control gets keyboard focus.
focusLost() Invoked when control loses keyboard focus.
Abstract methods declared in interface ActionListener
Method Purpose
actionPerformed() Invoked when button control is pressed.
Abstract methods declared in interface AdjustmentListener
Method Purpose
adjustmentValueChanged() Invoked when user scrolling using scrollbar button.
Abstract methods declared in interface ItemListener
Method Purpose
itemStateChanged() Invoked when state of the checkbox/radio button changed.
Abstract methods declared in interface TextListener
Method Purpose
itemStateChanged() Invoked when state of the checkbox/radio button changed.
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* Adapter Classes *
 To handle event, we have to implement the interfaces defined as listeners.
 We know that when an interface is implemented all the abstracts methods of
that interface must be defined in a class which is implementing it.
 A listener interface may contain multiple abstract methods.
 We cannot implement an interface by defining few of the methods of the
interface rather we have to define all the abstract methods of that interface.
 Java provides special classes called Adapter classes, that we can use to handle
only some of the events by implementing only those methods that we require
to handle the events.
 For example, The interface FocusListener has two methods to handle two
events i.e. focusGained() and focusLost(). If we want to handle only one
event, then by using adapter class associated with FocusListener interface we
can implement only one of these two methods.
 The following table shows the adapter classes provided in Java and its
associated interface listener:
Adapter Class Listener Interface
WindowAdapter WindowListener
FocusAdapter FocusListener
MouseAdapter MouseListener
MouseMotionAdapter MouseMotionListener

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For example,
 In above code, we are implementing FocusListner interface which has two
abstract methods i.e. focusGained() and focusLost().
 This code will produce error that implementation of focusLost() method is
missing. That means we must define both abstract methods while
implementing FocusListener interface. Although we don’t want handle focus
lost event.
 This problem will be resolved by using adapter class FocusAdapter as shown
in following program.
import java.awt.*; import java.awt.event.*;
public class test implements FocusListener
{
Frame obj;
{
test x=new test();
}
test()
{
obj=new Frame();
TextField t1=new TextField(); obj.add(t1);
Button b1=new Button("red"); obj.add(b1);
b1.addFocusListener(this);
}
// Only focusGained event we want handle
public void focusGained(FocusEvent z)
{
obj.setBackground(Color.RED);
}
}
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 The error occurred in previous programs is removed in this code by using
FocusAdapter Class instead of FocusListener interface.
import java.awt.*; import java.awt.event.*;
public class test extends FocusAdapter
{
Frame obj;
{
test x=new test();
}
test()
{
obj=new Frame();
TextField t1=new TextField(); obj.add(t1);
Button b1=new Button("red"); obj.add(b1);
b1.addFocusListener(this);
}
// Only focusGained event we want handle
public void focusGained(FocusEvent z)
{
obj.setBackground(Color.RED);
}
}

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* Inner Class *
 Inner classes are a security mechanism in Java.
 We know a class cannot be associated with the access modifier private, but if
we have the class as a member of other class, then the inner class can be made
private.
 Creating an inner class is quite simple. You just need to write a class within a
class.
In the given example, we make the inner class private and access the class through
a method.
Output:
This is inner class
class Outer_Demo
{
int num;
private class Inner_Demo // inner class
{
public void print()
{
System.out.println("This is an inner class");
}
}
// Accessing he inner class from the method within
void display_Inner()
{
Inner_Demo inner = new Inner_Demo();
inner.print();
}
}
public class innerclass
{
{
Outer_Demo outer = new Outer_Demo();
outer.display_Inner();
}
}

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B.Sc. III(VI Sem) Advance Java Unit3: AWT & Event Handling