事件监听是指当某个事件发生的时候干一些什么。

例如之前在关闭frame窗口时就写过一个window窗口监听，当点击左上角❌时调用System.exit进行程序关闭。

1.按钮监听

下面的例子是监听按钮Button被点击时触发的事件

同时我们将窗口关闭监听事件进行了优化，将windowCloseing写为一个方法，在使用时直接调用不用再进行方法的重写。

package YMP.GUI;
​
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
​
public class TestActionEvent {public static void main(String[] args) {Frame frame=new Frame();Button button=new Button("Button");
​//通过addActionListener()给button添加监听//addActionListener需要ActionListener接口，所以构造一个ActionListener
​//button添加监听，当button被点击时调用MyActionListener（）button.addActionListener(new MyActionListener());frame.add(button,BorderLayout.CENTER);
​frame.setSize(200,200);frame.setVisible(true);
​//调用windowClose方法关闭窗口windoeClose(frame);}//关闭窗口事件private static void windoeClose(Frame frame){frame.addWindowListener(new WindowAdapter() {@Overridepublic void windowClosing(WindowEvent e) {System.exit(0);}});}
}
​
class MyActionListener implements ActionListener{@Overridepublic void actionPerformed(ActionEvent e) {System.out.println("aaa");//当监听到行为时的事件：输出aaa}
}

2.两个按钮共用一个监听

package YMP.GUI.ActionListener;
​
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
​
public class TestActionListener2 {public static void main(String[] args) {Frame frame=new Frame();Button button1=new Button("Start" );Button button2=new Button("Stop" );
​button1.addActionListener(new MyMonitor());button2.addActionListener(new MyMonitor());
​button2.setActionCommand("bton2-stop");//这里设置了ActionCommand
​frame.add(button1,BorderLayout.NORTH);frame.add(button2,BorderLayout.SOUTH);
​frame.setSize(200,200);frame.setVisible(true);windowClose(frame);
​}private static void windowClose(Frame frame){frame.addWindowListener(new WindowAdapter() {@Overridepublic void windowClosing(WindowEvent e) {System.exit(0);}});}
}
class MyMonitor implements ActionListener{
​@Overridepublic void actionPerformed(ActionEvent e) {//e.getActionCommand(); 获得按钮信息ActionCommand，若不加修改则默认为按钮labelSystem.out.println(e.getActionCommand());//这里在控制台输出了Command
​//通过if语句判断两个按钮，使得两个按钮共用一个监听if(e.getActionCommand().equals("Start")){System.out.println("Start按钮");}if(e.getActionCommand().equals("bton2-stop")){System.out.println("Stop按钮");}}
}

3.输入框监听事件（TextField）

package YMP.GUI.ActionListener;
​
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
​
public class TestTextField {public static void main(String[] args) {new MyFrame();windowClose(new MyFrame());}private static void windowClose(Frame frame){frame.addWindowListener(new WindowAdapter() {@Overridepublic void windowClosing(WindowEvent e) {System.exit(0);}});}
​
}
​
class MyFrame extends Frame {public MyFrame() {TextField textField = new TextField();//创建文本框对象add(textField);
​textField.addActionListener(new MyTextActionListener());
​setSize(500, 80);setVisible(true);
​//设置置换编码// textField.setEchoChar('*');}
}
​class MyTextActionListener implements ActionListener {
​
​@Overridepublic void actionPerformed(ActionEvent e) {TextField field = (TextField) e.getSource();//获得资源，返回对象System.out.println(field.getText());//输出文本框内容field.setText("");//设置回车后文本框清空}}
​
​

4.简易计算器

制作以下图片所示简易计算器

过程设计

1.图示计算器是由3个text field，一个label和一个button组合

2.第一，二个文本框用于接收用户输入信息，button按下在第三个文本框输出结果

代码实现

![屏幕截图 2024-06-12 203920](C:\Users\youmu\Pictures\Screenshots\屏幕截图 2024-06-12 203920.png)package YMP.GUI.ActionListener;
​
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
​
public class TestCalc {public static void main(String[] args) {new Calculator();}
}
class Calculator extends Frame{public Calculator(){TextField T1=new TextField(10);//columns 可输入最大个数TextField T2=new TextField(10);TextField T3=new TextField(20);
​Button button=new Button("=");Label label=new Label("+");
​setLayout(new FlowLayout());add(T1);add(label);add(T2);add(button);add(T3);
​pack();setVisible(true);
​button.addActionListener(new MyCalculatorListenner(T1,T2,T3));
​addWindowListener(new WindowAdapter() {@Overridepublic void windowClosing(WindowEvent e) {System.exit(0);}});}
}
class MyCalculatorListenner implements ActionListener{private TextField T1,T2,T3;public MyCalculatorListenner(TextField T1,TextField T2,TextField T3){this.T1=T1;this.T2=T2;this.T3=T3;
​}
​@Overridepublic void actionPerformed(ActionEvent e) {int n1=Integer.parseInt(T1.getText());int n2=Integer.parseInt(T2.getText());T3.setText(""+(n1+n2));T1.setText("");T2.setText("");}
}

代码优化，完全面向对象

既然我们使用的是java，就该运用java的特长面向对象

package YMP.GUI.ActionListener;
​
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
​
public class TestCalc {public static void main(String[] args) {new Calculator().loadFrame();}
}
class Calculator extends Frame{//属性TextField T1,T2,T3;
​//方法public void loadFrame(){T1=new TextField(10);//columns 可输入最大个数T2=new TextField(10);T3=new TextField(20);
​Button button=new Button("=");Label label=new Label("+");
​setLayout(new FlowLayout());add(T1);add(label);add(T2);add(button);add(T3);
​pack();setVisible(true);
​button.addActionListener(new MyCalculatorListenner(this));
​addWindowListener(new WindowAdapter() {@Overridepublic void windowClosing(WindowEvent e) {System.exit(0);}});
​}public Calculator(){
​}
}
class MyCalculatorListenner implements ActionListener{//获得计算器对象，在一个类中组合另一个类Calculator calculator=null;public MyCalculatorListenner(Calculator calculator){this.calculator=calculator;
​}
​@Overridepublic void actionPerformed(ActionEvent e) {int n1=Integer.parseInt(calculator.T1.getText());int n2=Integer.parseInt(calculator.T2.getText());
​calculator.T3.setText(""+(n1+n2));calculator.T1.setText("");calculator.T2.setText("");}
}

两个代码效果都是一样的，但是第二个完全面向对象，第一个面向过程。

高级！！！