Java 內部類和匿名類 實現JButton動作 ActionListener類

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

public class ControlCircle2 extends JFrame {
    private JButton jbtEnlarge=new JButton("Enlarge");
    private JButton jbtShrink=new JButton("Shrink");
    private CirclePanel canvas=new CirclePanel();
    
    public ControlCircle2(){
        JPanel panel=new JPanel();
        panel.add(jbtEnlarge);
        panel.add(jbtShrink);
        this.add(canvas,BorderLayout.CENTER);
        this.add(panel, BorderLayout.SOUTH);
        
        jbtEnlarge.addActionListener(new EnlargeListener());
        jbtShrink.addActionListener(new ShrinkListener());
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ControlCircle2 frame=new ControlCircle2();
        frame.setTitle("ControlCircle2");
        frame.setSize(200,200);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);

    }
    class ShrinkListener implements ActionListener{
        @Override
        public void actionPerformed(ActionEvent e) {
            // TODO Auto-generated method stub
            canvas.shrink();
        }
    }
    class EnlargeListener implements ActionListener{
        @Override
        public void actionPerformed(ActionEvent e) {
            // TODO Auto-generated method stub
            canvas.enlarge();
        }
    }
    
}
class CirclePanel extends JPanel {
    private int radius=5;
    public void enlarge(){
        radius++;
        repaint();
    }
    public void shrink(){
        if(radius>=1){
        radius--;
        repaint();}
        else
            JOptionPane.showMessageDialog(null, "Radius can not less than 1.");
    }
    protected void paintComponent(Graphics g){
        super.paintComponent(g);
        g.drawOval(getWidth()/2-radius, getHeight()/2,
                2*radius, 2*radius);
    }

}

為了讓actionPerformed方法可以訪問到canvas變量，將EnlargeListener定義為ControlCircle2類的內部類。

匿名內部類是沒有名字的內部類，它一步完成定義內部類和創建一個該類的實例。

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

public class AnonymousListenerDemo extends JFrame {
    public AnonymousListenerDemo(){
        JButton jbtNew=new JButton("New");
        JButton jbtOpen=new JButton("Open");
        JButton jbtSave=new JButton("Save");
        JButton jbtPrint=new JButton("Print");
        
        JPanel panel=new JPanel();
        panel.add(jbtNew);
        panel.add(jbtOpen);
        panel.add(jbtSave);
        panel.add(jbtPrint);
        
        add(panel);
        
        jbtNew.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e){
                System.out.println("Process New");
            }
        });//匿名內部類
        
        jbtOpen.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent e){
                System.out.println("Process Open");
            }
        });
        
        jbtSave.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent e){
                System.out.println("Process Save");
            }
        });
        
        jbtPrint.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent e){
                System.out.println("Process Print");
            }
        });
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        AnonymousListenerDemo frame=new AnonymousListenerDemo();
        frame.setTitle("AnonymousListenerDemo");
        frame.pack();//程序沒有使用setSize方法來設置框架的大小，而是使用pack方法，可以根據組件的大小來自動調整框架的大小。
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);

    }

}

 還可以只使用一個actionListener，通過獲取ActionEvent的類別，來觸發相應的動作。

class ButtonListener implements ActionListener {
        @Override
        public void actionPerformed(ActionEvent e) {
            // TODO Auto-generated method stub
            if(e.getSource()==jbtNew)//使用getSource方法，獲得事件的對象，然后使用對應的動作。
                {System.out.println("Process New");
                JOptionPane.showMessageDialog(null, "Process New");}
            else if(e.getSource()==jbtOpen)
                {System.out.println("Process Open");
                JOptionPane.showMessageDialog(null, "Process Open");}
            else if(e.getSource()==jbtSave)
                {System.out.println("Process Save");
                JOptionPane.showMessageDialog(null, "Process Save");}
            else if(e.getSource()==jbtPrint)
                {System.out.println("Process Print");
                JOptionPane.showMessageDialog(null, "Process Print");}
        }
    }