Java基礎學習之Swing事件監聽
一、初始代碼架構
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("事件監聽測試");
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);
}
}
運行的結果
二、需求分析
想要點擊按鈕的時候在終端打印一行信息（比如”按鈕被點擊”）
產品爸爸，提瞭新需求，不能實現也要創造辦法實現的啦
2.1 寫監聽器
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Btn{
public static void main(String []args){
JFrame f = new JFrame("事件監聽測試");
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");
/**
* 事件監聽的使用步驟：
* 1. 創建監聽聽
* 2. 將監聽器註冊到按鈕上
*
*/
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("按鈕被點擊瞭----");
}
}
點擊按鈕的結果
2.2 發現問題
中規中矩地實現監聽器地話，發現要另外寫一個類實現
ActionListener接口地方法，使得代碼架構顯得比較臃腫。
2.3 使用匿名內部類優化代碼
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Btn{
public static void main(String []args){
JFrame f = new JFrame("事件監聽測試");
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");
/**
* 事件監聽的使用步驟：
* 1. 創建監聽聽
* 2. 將監聽器註冊到按鈕上
*
*/
ActionListener bl = new ActionListener(){
@Override
public void actionPerformed(ActionEvent e){
System.out.println("匿名內部類優化----");
}
};
btn.addActionListener(bl);
page.add(btn);
f.setVisible(true);
}
}
class btnListener implements ActionListener{
@Override
public void actionPerformed(ActionEvent e){
System.out.println("按鈕被點擊瞭----");
}
}
2.4 優化完之後發現還是不是很優雅
因為每次監聽都有重復代碼
@Override
public void actionPerformed(ActionEvent e){
System.out.println("匿名內部類優化----");
}
2.5 使用Lambda表達式再優化
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Btn{
public static void main(String []args){
JFrame f = new JFrame("事件監聽測試");
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");
/**
* 事件監聽的使用步驟：
* 1. 創建監聽聽
* 2. 將監聽器註冊到按鈕上
*
*/
// ActionListener bl = new ActionListener(){
// @Override
// public void actionPerformed(ActionEvent e){
// System.out.println("匿名內部類優化----");
// }
// };
// btn.addActionListener(bl);
btn.addActionListener((e)->{
System.out.println("使用Lambda表達式優化");
});
page.add(btn);
f.setVisible(true);
}
}
class btnListener implements ActionListener{
@Override
public void actionPerformed(ActionEvent e){
System.out.println("按鈕被點擊瞭----");
}
}
結果
2.6 最終的代碼
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Btn{
public static void main(String []args){
JFrame f = new JFrame("事件監聽測試");
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表達式優化");
});
page.add(btn);
f.setVisible(true);
}
}
三、ActionListener接口源碼
/*
* 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 <a href="https://docs.oracle.com/javase/tutorial/uiswing/events/actionlistener.html" rel="external nofollow" >How to Write an Action Listener</a>
*
* @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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