JApplet

1. Introduction
2. Hello World Example
3. More complex example using dialog boxes
4. Example with content pane.

1. INTRODUCTION

Java Swing includes a class JApplet contained in the javax.swong package) which replaces the Applet found in previous examples. A trivail example using the JApplet class is presented below in Table 1:

2. HELLO WORLD EXAMPLE

The copde given in Table 1 is the the standrad "Hello World" program as a JApplet.

// Hello World Japplet Example
// Frans Coenen
// 13 June 3003
// University of Liverpool

// Java Core Packages
import java.awt.Graphics;

// Jave extension packages
import javax.swing.JApplet;


public class HelloWorldJApplet extends JApplet {

    public void paint(Graphics g) {
        // Call super  class constuctors
        super.paint(g);

        // Hello word
        g.drawString("Helo Word in a JApplet",25,25);
        }
    }

Table 1: Hellow Word JApplet

Here is the applet

3. MORE COMPLEX EXAMPLE USING DIALOG BOXES

The code presented in Table 2 gives a more complex JApplet using input and message dialog boxes.

// ADDITION Japplet Example
// Frans Coenen
// 13 June 3003
// University of Liverpool

// Java Core Packages
import java.awt.Graphics;

// Jave extension packages
import javax.swing.*;


public class AdditionJApplet extends JApplet {

    /* ------ FIELDS ------ */
    int num1, num2 = 0;
    boolean errorFlag=false;

    final int START = 1;
    final int END   = 10;

    /* INITILISE JAPPLET */

    public void init() {
        String stNum1, stNum2;

        try{
            // Get first number]
            while  (true) {
                stNum1 = JOptionPane.showInputDialog("Enter first integer value between " + START +
        		" and " + END);
                num1   = Integer.parseInt(stNum1);
                if (num1>=START && num1<=END) break;
                JOptionPane.showMessageDialog(null,"ERROR 1: Input for first integer value " +
                	" must be a between " + START + " and " + END);
                }
	    // Get second number
            while  (num2END) {
                stNum2 = JOptionPane.showInputDialog("Enter second integer value between " + START +
        		" and " + END);
                num2   = Integer.parseInt(stNum2);
                if (num2>=START && num2<+END) break;
                JOptionPane.showMessageDialog(null,"ERROR 2: Input for second integer value " +
                	" must be a between " + START + " and " + END);
                	
                }
            }
        catch(NumberFormatException e) {
            errorFlag=true;
            }
	}

    /* PAINT */

    public void paint(Graphics g) {
        // Call super  class conastuctors
        super.paint(g);

        // Hello word
        g.drawRect(15,10,270,20);
        if (errorFlag) g.drawString("Operation canceled",25,25);
        else g.drawString("The sum is " + (num1+num2),25,25);
        }
    }

Table 2: More complicated JApplet

Here is the applet:

4. EXAMPLE WITH CONTENT PANE

Code in Table 3 retrieves the applrets content pane and then adds to this.

// TEXT AREA Japplet Example
// Frans Coenen
// 13 June 3003
// University of Liverpool

// Java Core Packages
import java.awt.*;
import java.awt.event.*;

// Jave extension packages
import javax.swing.*;

public class TextAreaJApplet extends JApplet implements ActionListener {

    /* ------ FIELDS ------ */
    JTextArea textArea1, textArea2;

    /* INITILISE JAPPLET */

    public void init() {
        // Get the applet's GUI component display area
        Container container = getContentPane();
        container.setBackground(Color.pink);
        container.setLayout(new FlowLayout());

        // Text area 1
        String string = "Some text in here, Some text in here, Some text in here";
        textArea1 = new JTextArea(string, 10, 15);
        container.add(new JScrollPane(textArea1));
	
        // Copy button
        JButton copyButton = new JButton("COPY");
        copyButton.addActionListener(this);
        container.add(copyButton);

	// Text area 2
	textArea2 = new JTextArea(10, 15);
	textArea2.setEditable(false);
        container.add(new JScrollPane(textArea2));
        }

    public void actionPerformed(ActionEvent event) {
        textArea2.setText(textArea1.getSelectedText());
        }
    }

Table 3: JApplet with content pane