A good answer might be:

There is no listener for the button's events. If there is no listener for a particular type of event, then the program ignores events of that type.

Details

There is a listener for the frame's "close button," but not for the button. You can click the button, and generate an event, but no listener receives the event.

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

public class ButtonDemo extends JFrame
{
  JButton bChange ; 

  // constructor for ButtonDemo
  ButtonDemo() 
  {
    // construct a Button
    JButton 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 );  
  }
}

The program in the previous chapter does not define a constructor because it inherits the constructor from its parent class (JFrame), which is enough to do the job. When you add components to a container, you need to define a constructor for the frame.

QUESTION 5:

First let us look at the problem of the button that fills the frame. What size to you think would be better for the button? Where do you think the button should go?