Anonymous Class

• You can declare an inner class has no name.
• You can define the class, and create an object of that type as a parameter all in one line.

start	press "add 1" 9 times
press "subtract 1" once	press "reset to 0"

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

public class AnonymousTest extends JFrame {
    // create 4 components, 3 buttons and one label
    private JButton addButton = new JButton("add 1");
    private JButton subtractButton = new JButton("subtract 1");
    private JButton resetButton = new JButton("Reset to 0");
    private JLabel countLabel = new JLabel("0", JLabel.CENTER);
    // count
    private int count = 0;
    // contentPane
    private Container contentPane = getContentPane();
    
    public AnonymousTest() {
        // set layout
        contentPane.setLayout(new GridLayout(4,1));
        // add components to the frame
        contentPane.add(addButton);
        contentPane.add(subtractButton);
        contentPane.add(resetButton);
        contentPane.add(countLabel);
        
        addButton.addActionListener(
            // anonymous class
            new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                   count++;
                   countLabel.setText(Integer.toString(count));
                }
           }// end of anonymous class
        );
        
        subtractButton.addActionListener(
            // anonymous class
            new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                   count--;
                   countLabel.setText(Integer.toString(count));
                }
           }// end of anonymous class
        );
        
        resetButton.addActionListener(
            // anonymous class
            new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                   count = 0;
                   countLabel.setText(Integer.toString(count));
                }
           }// end of anonymous class
        );
        
    }
    
    
    public static void main(String[] args) {
        AnonymousTest f = new AnonymousTest();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.pack();
        f.setVisible(true);
    }
}

• There are 3 different actions : add one, subtract one and reset to 0
• create 3 anonymoues class for 3 different actions
• the highlight parts (a)define a class, (b) create an instance at the same time.
• able to access the outer class( AnonymousTest)'s member variable. Example, the codes can access count and countLabel.
• anonymous class is convenient to use. You don't have to create 3 seperate inner classes like the examples gave in last lecture note.
• Anonymous classes can make code difficult to read. You should limit their use to those classes that are very small (no more than a method or two) and whose use is well-understood (like the AWT event-handling adapter classes).

new ClassName() { 
   // your codes
   // override methods
}

new ActionListener() {
   public void actionPerformed(ActionEvent e) {
      // codes
   }
}