Java中为按钮添加监听器(事件处理）四种形式总结

拼搏现实的明天。 2022-05-28 10:28 178阅读 0赞

以下的示例程序是要在一个面板中添加三个按钮，并分别添加三个监听器对象用来作为按钮的动作监听器，当点击不同的按钮时使得面板的背景色变成相应的颜色：

import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;
    
    public class ButtonFrame{
    	public static void main(String[] args){
    	    EventQueue.invokeLater(() -> {
        	        JFrame frame= new CreatButtonFrame();
                    frame.setTitle("ButtonTest");
                    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                    frame.setVisible(true);});	
    	}
    }
    
    class CreatButtonFrame extends JFrame{
    	private JPanel buttonPanel;
    	private static final int DEFAULT_WIDTH = 300;
    	private static final int DEFAULT_HEIGHT = 200;
    	public CreatButtonFrame(){
    		setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
    	    JButton yellowButton = new JButton("Yellow");
    	    JButton blueButton = new JButton("Blue");
    	    JButton redButton = new JButton("Red");
    	    buttonPanel = new JPanel();
    	    buttonPanel.add(yellowButton);
    	    buttonPanel.add(blueButton);
    	    buttonPanel.add(redButton);
    	    add(buttonPanel);
    	    ColorAction yellowAction = new ColorAction(Color.YELLOW);
    	    ColorAction blueAction = new ColorAction(Color.BLUE);
    	    ColorAction redAction = new ColorAction(Color.RED);
    	    yellowButton.addActionListener(yellowAction);
    	    blueButton.addActionListener(blueAction);
    	    redButton.addActionListener(redAction);
    	}
    	
    	class ColorAction implements ActionListener{
    		private Color backgroundColor;
    		public ColorAction(Color c){
    			backgroundColor = c;
    		}
    		public void actionPerformed(ActionEvent event){
    			buttonPanel.setBackground(backgroundColor);
    		}
    	}
    }

以上程序没必要单独为事件监听器定义一个类并构造类的3个对象，因此，可以使用lambda表达式简化如下：

此外，当我们不习惯于使用lambda表达式，而是更喜欢创建实现了ActionListener接口的事件源容器，然后这个容器再设置自身作为监听器，则可以修改为如下的形式:

import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;
    
    public class ButtonFrame{
    	public static void main(String[] args){
    		EventQueue.invokeLater(() -> {
        	JFrame frame= new CreatButtonFrame();
            frame.setTitle("ButtonTest");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setVisible(true);});	
    	}
    }
    
    class CreatButtonFrame extends JFrame implements ActionListener{
    	private JPanel buttonPanel;
    	private static final int DEFAULT_WIDTH = 300;
    	private static final int DEFAULT_HEIGHT = 200;
    	private Button yellowButton,blueButton,redButton;
    	public CreatButtonFrame(){
    		setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
    		buttonPanel = new JPanel();
    		yellowButton=new Button("yellow");
    		blueButton=new Button("blue");
    		redButton=new Button("red");
    		yellowButton.addActionListener(this);
    		blueButton.addActionListener(this);
    		redButton.addActionListener(this);
    		buttonPanel.add(yellowButton);
    		buttonPanel.add(blueButton);
    		buttonPanel.add(redButton);
    		add(buttonPanel);
    	}
    	public void actionPerformed(ActionEvent event) {
    		Object source=event.getSource();
    		if(source==yellowButton) {
    			buttonPanel.setBackground(Color.yellow);
    		}else if(source==blueButton) {
    			buttonPanel.setBackground(Color.blue);
    		}else if(source==redButton){
    			buttonPanel.setBackground(Color.red);
    		}
    	}
    }

此外，还可以采用一种机制指定事件监听器，其事件处理器包含一个方法调用。例如当一个按钮监听器需要执行调用:

frame.doMethod();

可以通过EventHandler类创建一个监听器：

EventHandler.create(ActionListener.class,frame,"doMethod")

但利用lambda表达式更容易实现：

event -> frame.doMethod();

因此，这种通过EventHandler类创建监听器的方法不常用。该方法的完整示例如下，该示例在点击按钮“Click Here”后会打印“Hello World！”的消息：

import java.awt.*; 
    import java.awt.event.*; 
    import javax.swing.*; 
    import java.beans.*; 
    public class Buttonhand extends JFrame{
    	public static void main(String args[]){
    		JFrame frame = new Buttonhand(); 
    		frame.setSize(300, 400); 
    		frame.setVisible(true); 	
    	}
    	public Buttonhand(){
    		super("事件处理"); 
    		setDefaultCloseOperation(EXIT_ON_CLOSE); 
    		JButton button = new JButton("Click Here"); 
    		Container contentPane = getContentPane(); 
    		contentPane.add(button, BorderLayout.CENTER); 
    		button.addActionListener( (ActionListener)EventHandler.create( ActionListener.class, this, "print") ); 
    	}
    	public void print(){
    		System.out.println("Hello World!");	
    	} 
    }