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Chapter vi(class applet)
Class Applet describes how Java applets run inside web browsers and provides examples of creating and running simple applets using the Abstract Window Toolkit (AWT) and Swing. It discusses the basic lifecycle methods of applets like init(), start(), stop(), and destroy(). Sample applets are provided to demonstrate drawing shapes, displaying text, and handling button clicks to update the display. Applets are embedded in HTML files and run within the browser.
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Chapter vi(class applet)
- 1.
- 2. • applications liveand run inside the Web browser’s window. • How to run JavaApplet – Create File: A.java – Compile: A.java=> A.class – Create and Open A.html • there are two varieties of applets: – applets use the Abstract Window Toolkit (AWT) – Swing class Japplet
- 3. A.Java import java.applet.*; import java.awt.*; publicclass A extends Applet{ private int w, h; public void init( ) { w = 45; h = 50; } public void paint(Graphics g){ g.drawRect(w, h, 20, 80); } } A.html <html> <applet code="A.class" height=200 width=320> </applet> </html>
- 4. public class JappletTest1extends Applet { // Called first. public void init() { // initialization } /* Called second, after init(). Also called whenever the applet is restarted. */ public void start() { // start or resume execution } // Called when the applet is stopped. public void stop() { // suspends execution } /* Called when applet is terminated. This is the last method executed. */ public void destroy() { // perform shutdown activities } // Called when an applet's window must be restored. public void paint(Graphics g) { // redisplay contents of window } }
- 5. import java.awt.*; import java.applet.*; publicclass Japplet1 extends Applet{ String msg; public void init() { setBackground(Color.cyan); setForeground(Color.red); msg = "Inside init( ) --"; } public void start(){ msg += " Inside start( ) --"; } public void paint(Graphics g) { msg += " Inside paint( )."; g.drawString(msg, 10, 30); } }
- 6. import java.awt.*; import java.awt.event.*; importjava.applet.*; public class AppletFrame extends Applet implements ActionListener { String msg = ""; Button yes, no, maybe; public void init() { yes = new Button("Yes"); no = new Button("No"); maybe = new Button("Undecided"); add(yes); add(no); add(maybe); yes.addActionListener(this); no.addActionListener(this); maybe.addActionListener(this); } public void actionPerformed(ActionEvent ae) { String str = ae.getActionCommand(); if(str.equals("Yes")) { msg = "You pressed Yes."; } else if(str.equals("No")) { msg = "You pressed No."; } else { msg = "You pressed Undecided."; } repaint(); } public void paint(Graphics g) { g.drawString(msg, 6, 100); } }
- 7. <html> <applet code ="Applet1.class" width = "300" height = "45"></applet> </html>
Editor's Notes
- #8 import java.awt.Graphics; // program uses class Graphics import javax.swing.JApplet; // program uses class JApplet public class Applet1 extends JApplet { // draw text on applet's background public void paint( Graphics g ) { // call superclass version of method paint super.paint( g ); // draw a String at x-coordinate 25 and y-coordinate 25 g.drawString( "Welcome to Computer Backanot!", 25, 25 ); } // end method paint } // end class WelcomeApplet
- #9 import java.awt.Graphics; // program uses class Graphics import javax.swing.JApplet; // program uses class JApplet import javax.swing.JOptionPane; // program uses class JOptionPane public class Applet1 extends JApplet { private double sum; // sum of values entered by user // initialize applet by obtaining values from user public void init () { String firstNumber; // first string entered by user String secondNumber; // second string entered by user double number1; // first number to add double number2; // second number to add // obtain first number from user firstNumber = JOptionPane.showInputDialog("Enter first floating-point value" ); // obtain second number from user secondNumber = JOptionPane.showInputDialog( "Enter second floating-point value" ); // convert numbers from type String to type double number1 = Double.parseDouble( firstNumber ); number2 = Double.parseDouble( secondNumber ); sum = number1 + number2; // add numbers } // end method init // draw results in a rectangle on applet's background public void paint( Graphics g ) { super.paint( g ); // call superclass version of method paint // draw rectangle starting from (15, 10) that is 270 // pixels wide and 20 pixels tall g.drawRect( 15, 10, 270, 20 ); // draw results as a String at (25, 25) g.drawString( "The sum is " + sum, 25, 25 ); } // end method paint } // end class AdditionApplet
- #10 import javax.swing.JApplet; // program uses class JApplet import java.awt.*; import java.awt.event.*; public class Applet1 extends JApplet { Button btSum,btMin,btDiv,btMult; TextField tfVal1,tfVal2,tfResult; public void init () { Frame frm = new Frame("Calculation"); Panel P1=new Panel(); P1.setLayout(new GridLayout(3,2)); P1.add(new Label("Value 1:"));P1.add(tfVal1=new TextField(20)); P1.add(new Label("Value 2:"));P1.add(tfVal2=new TextField(20)); P1.add(new Label("Result:"));P1.add(tfResult=new TextField(20)); Panel P2=new Panel(); P2.add(btSum=new Button(" + "));P2.add(btMin=new Button(" - ")); P2.add(btDiv=new Button(" / "));P2.add(btMult=new Button(" * ")); Button btEx; P2.add(btEx=new Button("Exit")); Panel P=new Panel(); P.setLayout(new BorderLayout()); P.add(new Label(" Arithmatics Operation"),BorderLayout.NORTH); P.add(P1,BorderLayout.CENTER); P.add(P2,BorderLayout.SOUTH); frm.setSize(200,100); add(P); btSum.addActionListener( new ActionListener(){ public void actionPerformed(ActionEvent e) { tfResult.setText((Float.parseFloat(tfVal1.getText())+Float.parseFloat(tfVal2.getText()))+ ""); } }); btMult.addActionListener( new ActionListener(){ public void actionPerformed(ActionEvent e) { tfResult.setText((Float.parseFloat(tfVal1.getText())*Float.parseFloat(tfVal2.getText()))+ ""); } }); btDiv.addActionListener( new ActionListener(){ public void actionPerformed(ActionEvent e) { tfResult.setText((Float.parseFloat(tfVal1.getText())/Float.parseFloat(tfVal2.getText()))+ ""); } }); btMin.addActionListener( new ActionListener(){ public void actionPerformed(ActionEvent e) { tfResult.setText((Float.parseFloat(tfVal1.getText())-Float.parseFloat(tfVal2.getText()))+ ""); } }); btEx.addActionListener( new ActionListener(){ public void actionPerformed(ActionEvent e) { System.exit(0); } }); } // end method init } // end class AdditionApplet
- #11 import javax.swing.*; import javax.swing.JOptionPane; // program uses class JOptionPane import java.awt.*; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; public class Applet1 extends JApplet { JTextField jTfEn,jTfKh; JButton jBapply,jBexit,jBclear; public void init () { setSize(300, 200); JPanel jp1=new JPanel(); jp1.setLayout(new GridLayout(3,3)); JLabel jlEn=new JLabel("Enlish:");jp1.add(jlEn);jTfEn=new JTextField(20);jp1.add(jTfEn); Font font = new Font("Limon S1", Font.PLAIN, 30); JLabel jlKh=new JLabel("Khmer:");jp1.add(jlKh);jTfKh=new JTextField(20);jp1.add(jTfKh); jTfKh.setFont(font); JPanel jp2=new JPanel(); jp2.setLayout(new FlowLayout()); jBapply=new JButton("Apply");jp2.add(jBapply);jBexit=new JButton("Exit");jp2.add(jBexit); jBclear=new JButton("Clear");jp2.add(jBclear); JPanel jp=new JPanel(); jp.setLayout(new BorderLayout()); jp.add(jp1,BorderLayout.NORTH); jp.add(jp2,BorderLayout.CENTER); jBapply.addActionListener(new ActionListener(){ public void actionPerformed(ActionEvent e) { if(jTfEn.getText().equals("")) { JOptionPane.showMessageDialog(null,"Please, Enter English word bat!"); } else jTfKh.setText(jTfEn.getText()); } }); jBexit.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent arg0) { System.exit(0); } }); jBclear.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent arg0) { jTfKh.setText(""); jTfEn.setText(""); } }); add(jp); } // end method init } // end class AdditionApplet