20. Runtime Events

• Event-driven program expects various events in any order: user keystrokes, mouse clicks, minimizing windows, and so on

• Source: a component where the event is generated

• Listener: an object to be notified about the event and processing it

• To accept event messages, create a class that implements ActionListener:

  
      import java.awt.*;
      import java.awt.event.*;
      import javax.swing.*;
      import javax.swing.event.*;
  
      class MyButtonClickAction implements ActionListener
      {
          JButton mButton;
  
          public MyButtonClickAction( JButton button )
          {
              mButton = button;
          }
  
          /** 
          * Handles user clicks
          */
          public void actionPerformed( ActionEvent event )
          {
              mButton.setText( "Click!" );
          }
      }//class MyButtonClickAction
  
  

• Add action listener to the event source widget:

  
      JButton button = new JButton( "Hello" );
      button.addActionListener( new MyButtonClickAction( button ) );