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Applet in Java
Abhishek Singh
Advantage of Applet• There are many advantages of applet. They are
as follows : It works at client side so less response time.
• Secured• It can be executed by browsers running under
many plateforms , including Linux, Windows, Mac Os etc.
Notes :Applet is a special type of program that is embedded in the webpage to generate the dynamic content. It runs inside the browser and works at client side.
Drawback of Applet
• Plugin is required at client browser to execute applet.
Hierarchy of Applet
• As displayed in the above diagram, Applet class extends Panel. Panel class extends Container which is the subclass of Component.
Lifecycle of an Applet:
1. Applet is initialized.
2. Applet is started.
3. Applet is painted.
4. Applet is stopped.
5. Applet is destroyed.
Life cycle methods for Applet:
• java.applet.Applet class:• For creating any applet java.applet.Applet class must be
inherited. It provides 4 life cycle methods of applet.1. public void init(): is used to initialized the Applet. It is
invoked only once.2. public void start(): is invoked after the init() method or
browser is maximized. It is used to start the Applet.3. public void stop(): is used to stop the Applet. It is invoked
when Applet is stop or browser is minimized.4. public void destroy(): is used to destroy the Applet. It is
invoked only once.
The <applet> HTML Tag<applet code=classfilename.class width=applet_viewing_width_in_pixels height=applet_viewing_height_in_pixels [archive=archivefile] [codebase=applet_url] [vspace=vertical_margin] [hspace=horizontal_margin] [align=applet_alignment] [alt=alternative_text]><param name=param_name1 value=param_value1></applet>
Displaying Graphics in Applet(1)• java.awt.Graphics class provides many methods for graphics
programming.• Commonly used methods of Graphics class:– public abstract void drawString(String str, int x, int y): is used to
draw the specified string.– public void drawRect(int x, int y, int width, int height): draws a
rectangle with the specified width and height.– public abstract void fillRect(int x, int y, int width, int height): is
used to fill rectangle with the default color and specified width and height.
– public abstract void drawOval(int x, int y, int width, int height): is used to draw oval with the specified width and height.
– public abstract void fillOval(int x, int y, int width, int height): is used to fill oval with the default color and specified width and height.
Displaying Graphics in Applet(2)• public abstract void drawLine(int x1, int y1, int x2, int y2): is
used to draw line between the points(x1, y1) and (x2, y2).• public abstract boolean drawImage(Image img, int x, int y,
ImageObserver observer): is used draw the specified image.• public abstract void drawArc(int x, int y, int width, int height,
int startAngle, int arcAngle): is used draw a circular or elliptical arc.
• public abstract void fillArc(int x, int y, int width, int height, int startAngle, int arcAngle): is used to fill a circular or elliptical arc.
• public abstract void setColor(Color c): is used to set the graphics current color to the specified color.
• public abstract void setFont(Font font): is used to set the graphics current font to the specified font.
• import java.applet.Applet; • import java.awt.*; • public class GraphicsDemo
extends Applet{ • public void paint(Graphics
g){ • g.setColor(Color.red); • g.drawString("Welcome",5
0, 50); • g.drawLine(20,30,20,300); • g.drawRect(70,100,30,30); • g.fillRect(170,100,30,30); • g.drawOval(70,200,30,30);
• • g.setColor(Color.pink); • g.fillOval(170,200,30,30); • g.drawArc(90,150,30,30,30,
270); • g.fillArc(270,150,30,30,0,18
0); • • } • }
• myapplet.html• <html> • <body> • <applet code="GraphicsDemo.class" width="3
00" height="300"> • </applet> • </body> • </html>
Java AWT (Abstract Windowing Toolkit)
Abhishek Singh
Abstract Windowing Toolkit
• Java AWT (Abstract Windowing Toolkit) is an API to develop GUI or window-based application in java.
• Java AWT components are platform-dependent i.e. components are displayed according to the view of operating system. AWT is heavyweight i.e. its components uses the resources of system.
• The java.awt package provides classes for AWT api such as TextField, Label, TextArea, RadioButton, CheckBox, Choice, List etc.
Java AWT Hierarchy
• Container : The Container is a component in AWT that can contain another components like buttons, textfields, labels etc. The classes that extends Container class are known as container such as Frame, Dialog and Panel.
• Window : The window is the container that have no borders and menu bars. You must use frame, dialog or another window for creating a window.
• Panel :The Panel is the container that doesn't contain title bar and menu bars. It can have other components like button, textfield etc.
• Frame :The Frame is the container that contain title bar and can have menu bars. It can have other components like button, textfield etc.
Useful Methods of Component classMethod Description
public void add(Component c) inserts a component on this component.
public void setSize(int width,int height)
sets the size (width and height) of the component.
public void setLayout(LayoutManager m)
defines the layout manager for the component.
public void setVisible(boolean status)
changes the visibility of the component, by default false.
Java AWT Example
• To create simple awt example, you need a frame. There are two ways to create a frame in AWT.– By extending Frame class (inheritance)
– By creating the object of Frame class (association)
Simple example of AWT by inheritance• import java.awt.*; • class First extends Frame{ • First(){ • Button b=new Button("click me"); • b.setBounds(30,100,80,30);// setting button position • add(b);//adding button into frame • setSize(300,300);//frame size 300 width and 300 height • setLayout(null);//no layout manager • setVisible(true);//now frame will be visible, by default not visible • } • public static void main(String args[]){ • First f=new First(); • }• } The setBounds(int xaxis, int yaxis, int width, int height) method is used in the above example
that sets the position of the awt button.
Simple example of AWT by association(2)• import java.awt.*; • class First2{ • First2(){ • Frame f=new Frame(); • Button b=new Button("click me"); • b.setBounds(30,50,80,30); • f.add(b); • f.setSize(300,300); • f.setLayout(null); • f.setVisible(true); • } • public static void main(String args[]){ • First2 f=new First2(); • }}
AWT UI Components• The set of components – Labels– Buttons– Check Boxes (and Radio Buttons)– Text Entry Fields– Lists– Containers (to hold set of other UI elements)– Layout Managers (to control the positioning of other UI
elements within Containers)
To use a UI component, create an instance of it, then use the “add” method to place it under the control of a container (the basic applet window is such a container).
Label
• A component which displays a String. Cannot be modified by the user, but can be changed by the application.
• Why use a label instead of an ordinary text string?– You don’t have to redraw labels yourself using paint(). The
AWT keeps track of them and redraws them when needed.– Labels follow the layout of the container in which they are
placed, and can be aligned with other UI components.
Example of Label• import java.awt.Label;• /*<applet code=LabelTest.class
width="300" height="300"> • </applet> */• public class LabelTest extends java.applet.Applet {• public void init() {• add(new Label("This is a label"));• add(new Label("Another one“,Label.RIGHT));• }• }
Button
• A component which, when “clicked” with the mouse, triggers some action.• /*<applet code=ButtonTest.class width="300" height="300"> • </applet> */• import java.awt.Button;• public class ButtonTest extends java.applet.Applet {• public void init() {• add(new Button("Rewind"));• add(new Button("Play"));• add(new Button("Fast Forward"));• add(new Button("Stop"));• add(new Button("Eject"));• }• }
Check Box• A component which can be selected or unselected (checked or
unchecked) to provide options. Unlike buttons, check boxes are not normally used to trigger direct actions.
• import java.awt.Checkbox;• /*<applet code=CheckboxTest.class width="300" height="300"> • </applet> */• public class CheckboxTest extends java.applet.Applet {• public void init() {• add(new Checkbox("Compiler Design"));• add(new Checkbox("Intro to Java"));• add(new Checkbox("Java 2", true));• add(new Checkbox("C++"));• } }• Note the use of the 2-argument constructor to force the “Java 2”
Checkbox to be initially checked. Method getState(), returns true or false depending on whether the box is checked or not.
Radio Buttons• A set of Radio Buttons is a grouped collection of Checkboxes, only one of
which may be checked at a time. A set of radio buttons is made by first creating a CheckboxGroup object, then creating a number of Checkboxes and associating each one with the CheckboxGroup.
• import java.awt.Checkbox;• import java.awt.CheckboxGroup;• /*<applet code=RadiobuttonTest.class width="300" height="300"> • </applet> */• public class RadiobuttonTest• extends java.applet.Applet {• public void init() {• CheckboxGroup cbg = new CheckboxGroup();• add(new Checkbox("Happy", true, cbg));• add(new Checkbox("Sad", false, cbg));• }• }
• Note that Radio Buttons (exclusive choice) typically appear Round, whereas Check Boxes (nonexclusive choice) typically appear Square.
• Method getState() can be used to check the state of an individual radio button just as it can be used to interrogate a check box. Method getSelectedCheckbox() (defined in Checkbox-Group) can be used to find which radio button in a group is selected.
• Checkbox selected;• selected = cbg.getSelectedCheckbox();
Text Field• A component which allows a single line of text to be edited by the user.• import java.awt.Label;• import java.awt.TextField;• import java.awt.event.*;• public class TextFieldTest extends java.applet.Applet implements ActionListener {• public void init() {• TextField tf = new TextField(20);• tf.setEchoChar('?');• tf.addActionListener(this);• add(new Label("Password: ", Label.RIGHT));• add(tf);• }• public void actionPerformed(• ActionEvent e) {• String text = e.getActionCommand();• System.out.println(text);• }• }
• The text field generates an ActionEvent when the return key is pressed. The “action command” contains the text in the field at the time when the return key was pressed.
• The setEchoChar('?') method is used to change the echo character to ‘?’. This is useful for fields which are private (e.g., passwords). Note that if this method is not called, the text field will echo the character typed.
• To respond to changes in the text field implement a• “Text Listener”. This means that you have to create a class object
implementing the TextListener interface (i.e., a method called “textValueChanged”, and add this as a text listener to the TextField object.
• In the listener method, retrieve the current text like so:– TextField tf = (TextField) e.getSource();– String text = tf.getText();
import java.awt.Label;import java.awt.TextField;import java.awt.event.*;public class TextFieldTest2 extends java.applet.Applet implements ActionListener, TextListener {public void init() {TextField tf = new TextField(20);tf.addActionListener(this);tf.addTextListener(this);add(new Label("Name: ", Label.RIGHT));add(tf);}public void actionPerformed( ActionEvent e) {String text = e.getActionCommand();System.out.println("Action Event: “ + text);}public void textValueChanged( TextEvent e) {TextField tf = (TextField) e.getSource();String text = tf.getText();System.out.println("Text Event: " + text);}}
Choice Menu (List)• A component which allows the user to select one option from a
number presented in a menu format.• import java.awt.Choice;• public class ChoiceMenuTest• extends java.applet.Applet {• public void init() {• Choice c = new Choice();• c.add("Apples"); • c.add("Ornages");• c.add("Lemons");• c.add("Bananas");• add(c);• }• }
Event and Listener (Event Handling):
• Changing the state of an object is known as an event. For example, click on button, dragging mouse etc. The java.awt.event package provides many event classes and Listener interfaces for event handling.
Event classes and Listener interfaces:Event Classes Listener Interfaces
ActionEvent ActionListener
MouseEvent MouseListener and MouseMotionListener
MouseWheelEvent MouseWheelListener
KeyEvent KeyListener
ItemEvent ItemListener
TextEvent TextListener
AdjustmentEvent AdjustmentListener
WindowEvent WindowListener
ComponentEvent ComponentListener
ContainerEvent ContainerListener
FocusEvent FocusListener
Steps to perform EventHandling:
• Following steps are required to perform event handling :– Implement the Listener interface and overrides its
methods– Register the component with the Listener
• For registering the component with the Listener, many classes provide the registration methods. For example:
• Buttonpublic void addActionListener(ActionListener a){}
• MenuItempublic void addActionListener(ActionListener a){}
• TextFieldpublic void addActionListener(ActionListener a){}public void addTextListener(TextListener a){}
• TextAreapublic void addTextListener(TextListener a){}
• Checkboxpublic void addItemListener(ItemListener a){}
• Choicepublic void addItemListener(ItemListener a){}
• Listpublic void addActionListener(ActionListener a){}
public void addItemListener(ItemListener a){}
EventHandling Codes:
• We can put the event handling code into one of the following places:
– Same class
– Other class
– Annonymous class
• import java.awt.*; • import java.awt.event.*; • class AEvent extends Frame i
mplements ActionListener{ • TextField tf; • AEvent(){ • tf=new TextField(); • tf.setBounds(60,50,170,20); • Button b=new Button("click
me"); • b.setBounds(100,120,80,30); • b.addActionListener(this); • add(b);• add(tf);
• setSize(300,300); • setLayout(null); • setVisible(true); • } • public void actionPerformed(
ActionEvent e){ • tf.setText("Welcome"); • } • public static void main(String
args[]){ • new AEvent(); • } • }
Example of event handling by Outer class(1)
• import java.awt.*; • import java.awt.event.*; • class AEvent2 extends Frame impl
ements ActionListener{ • TextField tf; • AEvent2(){ • tf=new TextField(); • tf.setBounds(60,50,170,20); • Button b=new Button("click me"); • b.setBounds(100,120,80,30); • b.addActionListener(this); • add(b);add(tf); • setSize(300,300);
• setLayout(null); • setVisible(true); • } • public void actionPerformed(Actio
nEvent e){ • tf.setText("Welcome"); • } • public static void main(String args[
]){ • new AEvent2(); • } • }
Example of event handling by Outer class(2)
• import java.awt.event.*; • class Outer implements ActionListener{ • AEvent2 obj; • Outer(AEvent2 obj){ • this.obj=obj; • } • public void actionPerformed(ActionEvent e){ • obj.tf.setText("welcome"); • } • • }
Example of event handling by Annonymous class:
• import java.awt.*; • import java.awt.event.*; • class AEvent3 extends Frame{ • TextField tf; • AEvent3(){ • tf=new TextField(); • tf.setBounds(60,50,170,20); • Button b=new Button("click me
"); • b.setBounds(50,120,80,30); • b.addActionListener(new Actio
nListener(){ • public void actionPerformed()
{
• tf.setText("hello"); • } • }); • add(b);add(tf); • setSize(300,300); • setLayout(null); • setVisible(true); • } • public static void main(String a
rgs[]){ • new AEvent3(); • } • }
• import java.awt.*;• import java.applet.*;• import java.awt.event.*;• /*• <applet CODE=AdapDemo.class WIDTH=300
HEIGHT=200>• </applet>• */• public class AdapDemo extends Applet • {• public String myMessage = "x = ?, y = ?";• public void init()• {• // tell the applet to listen for mouse related
events addMouseListener(new MAdapter (this)); • }• public void paint(Graphics g)• {• System.out.println("paint called");
• g.drawString(myMessage, 50, 50);• }• }• class MAdapter extends MouseAdapter• {• AdapDemo ad;• MAdapter(AdapDemo ad)• {• this.ad=ad;• }• // Respond to a mouse press on applet• public void mousePressed(MouseEvent me) • {• // display the x and y coordinate of mouse pointer• ad.myMessage = "x = " + me.getX() + ", y = " +
me.getY();• ad.repaint();• }• }
KeyboardListener• import java.awt.*; • import java.awt.event.*;• public class KeyboardListener extends Frame
implements KeyListener• {• TextField myText;• Label myLabel;• public KeyboardListener(String s )• {
super(s); • Panel myPanel =new Panel();• myLabel = new Label ("Key Listener!" ) ;• myPanel.add(myLabel); • add(myPanel);• addKeyListener ( this ); • setSize ( 200,200 );• setVisible(true);• addWindowListener(new WindowAdapter()• {• public void windowClosing(WindowEvent we)• {• System.exit(0);
• }• });• }• public void keyTyped ( KeyEvent ke )• {• myLabel.setText("Key Typed");• char youTyped= ke.getKeyChar();• myLabel.setText("You press: " + youTyped );• }• public void keyPressed ( KeyEvent ke)• {• myLabel.setText ( "Key Pressed" ) ; • }• public void keyReleased ( KeyEvent ke )• {• myLabel.setText( "Key Released" ) ; • }• public static void main (String[]args )• {• new KeyboardListener( "KeyListener Tester" ) ; • }• }
MouseListenerDemo• import java.awt.*;• import java.applet.*;• import java.awt.event.*;• /*<applet CODE=MouseListenerDemo.class WIDTH=300
HEIGHT=200> </applet> */• public class MouseListenerDemo extends Applet
implements MouseListener• {• public String myMessage = "x = ?, y = ?";• public void init()• {• // tell the applet to listen for mouse related events• addMouseListener(this); • repaint();• }• public void paint(Graphics g)• {• System.out.println("paint called");• g.drawString(myMessage, 50, 50);• }• // Respond to a mouse press on applet• public void mousePressed(MouseEvent me) • {• // display the x and y coordinate of mouse pointer
• myMessage = "x = " + me.getX() + ", y = " + me.getY();• System.out.println("mouse button pressed");• repaint();• }• // you must implement all the methods of MouseListener
interface. • public void mouseClicked(MouseEvent e)• {• System.out.println("mouse button clicked");• }• public void mouseEntered(MouseEvent e)• {• System.out.println("mouse enter in application area");• }• public void mouseExited(MouseEvent e)• {• System.out.println("mouse exit in application area");• }• public void mouseReleased(MouseEvent e)• {• System.out.println("mouse button released");• }• }
MyActionListener• import javax.swing.*;• import java.awt.Button;• import java.awt.FlowLayout;• import java.awt.TextField;• import java.awt.event.*;• public class MyActionListener extends JFrame
implements WindowListener, • ActionListener• {• TextField text = new TextField(20);• Button b1;• private int numOfClicks = 0;• public static void main(String[] args)• {• MyActionListener myWindow = new
MyActionListener("Using ActonListener");• myWindow.setSize(350,200);• myWindow.setVisible(true);• }• public MyActionListener(String title)• {• super(title);• setLayout(new FlowLayout());• addWindowListener(this);
• b1 = new Button("Click me");• add(b1);• add(text);• b1.addActionListener(this);• }• public void actionPerformed(ActionEvent ae)• {• numOfClicks++;• text.setText("Button Clicked " + numOfClicks + "
times");• }• public void windowClosing(WindowEvent we)• {• dispose();• System.exit(0);• }• public void windowOpened(WindowEvent we) {}• public void windowActivated(WindowEvent we) {}• public void windowIconified(WindowEvent we) {}• public void windowDeiconified(WindowEvent we) {}• public void windowDeactivated(WindowEvent we) {}• public void windowClosed(WindowEvent we) {}• }
