Java————ActionListener

1、什么是ActionListener

与KeyListener相似，ActionListener也是一个继承了Event接口的接口，我们需要一个类来实现ActionListener接口或者继承一个实现了ActionListener接口的类，然后重写actionPerformed方法

ActionListener源码：

public interface ActionListener extends EventListener {
    /*** Invoked when an action occurs.*/public void actionPerformed(ActionEvent e);}

从源码中我们可以看出，ActionListener中只有一个方法，方法的参数为Action
Event，我们只要在实现ActionListener的类/继承了实现ActionListener的类中重写此方法即可，下面我们来了解一下ActionEvent

1.1 了解ActionEvent类

ActionEvent类是一个语义事件表明一个被定义的组件有行为发生，比如你在一个Button上增加了ActionListener，那么每当这个Button被点击（空格键也行）时，就会调用ActionListener类中重写的actionPerformed方法

2、ActionListener作用

ActionListener只有一个actionPerformed方法，当且注册了ActionListner的组件监听到了动作时，就会调用actionPerformed方法

下面是使用三部曲
(1) Implement the ActionListener interface in the class:

public class ActionListenerExample Implements ActionListener  

(2) Register the component with the Listener:

component.addActionListener(instanceOfListenerclass);

(3) Override the actionPerformed() method:

public void actionPerformed(ActionEvent e){
      //Write the code here}

使用示例：

import java.awt.*;  
import java.awt.event.*;  
//1st step 
public class ActionListenerExample implements ActionListener{
      
public static void main(String[] args) {
      Frame f=new Frame("ActionListener Example");  final TextField tf=new TextField();  tf.setBounds(50,50, 150,20);  Button b=new Button("Click Here");  b.setBounds(50,100,60,30);  //2nd step b.addActionListener(this);  f.add(b);f.add(tf);  f.setSize(400,400);  f.setLayout(null);  f.setVisible(true);   
}  
//3rd step 
public void actionPerformed(ActionEvent e){
      tf.setText("Welcome to Javatpoint.");  
}  
}  

输出：

3、ActionListener用法

• ActionListener实战：

package practice;import java.awt.*;
import java.awt.event.*;public class AL extends Frame implements WindowListener,ActionListener {
    TextField text = new TextField(20);Button b;private int numClicks = 0;public static void main(String[] args) {
    AL myWindow = new AL("My first window");myWindow.setBounds(400,400,350,100);myWindow.setLocationRelativeTo(null);myWindow.setVisible(true);}public AL(String title) {
    super(title);setLayout(new FlowLayout());addWindowListener(this);b = new Button("Click me");add(b);add(text);b.addActionListener(this);}@Overridepublic void actionPerformed(ActionEvent e) {
    numClicks++;text.setText("Button Clicked " + numClicks + " times");}@Overridepublic void windowClosing(WindowEvent e) {
    dispose();System.exit(0);}@Overridepublic void windowOpened(WindowEvent e) {
    }@Overridepublic void windowActivated(WindowEvent e) {
    }@Overridepublic void windowIconified(WindowEvent e) {
    }@Overridepublic void windowDeiconified(WindowEvent e) {
    }@Overridepublic void windowDeactivated(WindowEvent e) {
    }@Overridepublic void windowClosed(WindowEvent e) {
    }}

输出：