Java基础学习之Swing事件监听

一、初始代码架构

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


public class Btn extends JFrame{
    public static void main(String []args){
        JFrame f = new JFrame("事件监听测试");
        f.setBounds(0,0,300,400);
        f.addWindowListener(new WindowAdapter(){
            public void windowClosing(WindowEvent e){
                f.setVisible(false);
                f.dispose();
                System.exit(0);
            }
        });
        Container page = f.getContentPane();
        page.setLayout(new FlowLayout());
        JButton btn = new JButton("打印");
        page.add(btn);
        f.setVisible(true);
    }
    

}

运行的结果

二、需求分析

想要点击按钮的时候在终端打印一行信息（比如"按钮被点击"）

产品爸爸，提了新需求，不能实现也要创造办法实现的啦

2.1 写监听器

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


public class Btn{
    public static void main(String []args){
        JFrame f = new JFrame("事件监听测试");
        f.setBounds(0,0,300,400);
        f.addWindowListener(new WindowAdapter(){
            public void windowClosing(WindowEvent e){
                f.setVisible(false);
                f.dispose();
                System.exit(0);
            }
        });
        Container page = f.getContentPane();
        page.setLayout(new FlowLayout());
        JButton btn = new JButton("打印");

        /**
         * 事件监听的使用步骤：
         * 1. 创建监听听
         * 2. 将监听器注册到按钮上
         * 
         */
        btnListener bl = new btnListener();
        btn.addActionListener(bl);
        page.add(btn);
        f.setVisible(true);
    }

    
    

}

class btnListener implements ActionListener{
        @Override
        public void actionPerformed(ActionEvent e){
            System.out.println("按钮被点击了----");
        }
    }

点击按钮的结果

 

2.2 发现问题

中规中矩地实现监听器地话，发现要另外写一个类实现ActionListener 接口地方法，使得代码架构显得比较臃肿。

2.3 使用匿名内部类优化代码

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


public class Btn{
    public static void main(String []args){
        JFrame f = new JFrame("事件监听测试");
        f.setBounds(0,0,300,400);
        f.addWindowListener(new WindowAdapter(){
            public void windowClosing(WindowEvent e){
                f.setVisible(false);
                f.dispose();
                System.exit(0);
            }
        });
        Container page = f.getContentPane();
        page.setLayout(new FlowLayout());
        JButton btn = new JButton("打印");

        /**
         * 事件监听的使用步骤：
         * 1. 创建监听听
         * 2. 将监听器注册到按钮上
         * 
         */
        ActionListener bl = new ActionListener(){
            @Override
            public void actionPerformed(ActionEvent e){
                System.out.println("匿名内部类优化----");
            }
        };

        btn.addActionListener(bl);
        page.add(btn);
        f.setVisible(true);
    }

    
    

}

class btnListener implements ActionListener{
        @Override
        public void actionPerformed(ActionEvent e){
            System.out.println("按钮被点击了----");
        }
    }

2.4 优化完之后发现还是不是很优雅

因为每次监听都有重复代码

@Override
 public void actionPerformed(ActionEvent e){
     System.out.println("匿名内部类优化----");
 } 

2.5 使用Lambda表达式再优化

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


public class Btn{
    public static void main(String []args){
        JFrame f = new JFrame("事件监听测试");
        f.setBounds(0,0,300,400);
        f.addWindowListener(new WindowAdapter(){
            public void windowClosing(WindowEvent e){
                f.setVisible(false);
                f.dispose();
                System.exit(0);
            }
        });
        Container page = f.getContentPane();
        page.setLayout(new FlowLayout());
        JButton btn = new JButton("打印");

        /**
         * 事件监听的使用步骤：
         * 1. 创建监听听
         * 2. 将监听器注册到按钮上
         * 
         */
        // ActionListener bl = new ActionListener(){
        //     @Override
        //     public void actionPerformed(ActionEvent e){
        //         System.out.println("匿名内部类优化----");
        //     }
        // };

        // btn.addActionListener(bl);
        btn.addActionListener((e)->{
            System.out.println("使用Lambda表达式优化");
        });
        page.add(btn);
        f.setVisible(true);
    }

    
    

}

class btnListener implements ActionListener{
        @Override
        public void actionPerformed(ActionEvent e){
            System.out.println("按钮被点击了----");
        }
    }

结果

2.6 最终的代码

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Btn{
    public static void main(String []args){
        JFrame f = new JFrame("事件监听测试");
        f.setBounds(0,0,300,400);
        f.addWindowListener(new WindowAdapter(){
            public void windowClosing(WindowEvent e){
                f.setVisible(false);
                f.dispose();
                System.exit(0);
            }
        });
        Container page = f.getContentPane();
        page.setLayout(new FlowLayout());
        JButton btn = new JButton("打印");
        
        btn.addActionListener((e)->{
            System.out.println("使用Lambda表达式优化");
        });
        page.add(btn);
        f.setVisible(true);
    }
}

三、ActionListener接口源码

/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.awt.event;

import java.util.EventListener;

/**
 * The listener interface for receiving action events.
 * The class that is interested in processing an action event
 * implements this interface, and the object created with that
 * class is registered with a component, using the component's
 * {@code addActionListener} method. When the action event
 * occurs, that object's {@code actionPerformed} method is
 * invoked.
 *
 * @see ActionEvent
 * @see How to Write an Action Listener
 *
 * @author Carl Quinn
 * @since 1.1
 */
public interface ActionListener extends EventListener {

    /**
     * Invoked when an action occurs.
     * @param e the event to be processed
     */
    public void actionPerformed(ActionEvent e);

}

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