Example Program with a Button

Here is a sample program, nearly the same as the one in the previous chapter, with the addition of a button.

To construct a JButton object, use new, as with all classes. Now you have a JButton object, but you still need to do something with it.

import java.awt.*; 
import java.awt.event.*;
import javax.swing.*;

public class ButtonDemo extends JFrame
{
  JButton bChange ; // reference to the button object

  // constructor for ButtonDemo
  ButtonDemo() 
  {
    // construct a Button
    bChange = new JButton("Click Me!"); 

    // add the button to the JFrame
    getContentPane().add( bChange );     
  }

  public static void main ( String[] args )
  {
    ButtonDemo frm = new ButtonDemo();
    
    WindowQuitter wquit = new WindowQuitter();
    frm.addWindowListener( wquit );
    
    frm.setSize( 200, 150 );     
    frm.setVisible( true );      
  }
}

class WindowQuitter  extends WindowAdapter
{
  public void windowClosing( WindowEvent e )
  {
    System.exit( 0 );  
  }
}

This program adds a JButton to the frame when the frame is constructed.

The button (and other GUI components) are added to the frame's content pane. The content pane is a container that represents the main rectangle of the frame.

To get a reference to the content pane, use the getContentPane() method of the frame.