java怎么触发事件 java按钮触发事件

 

Button类的函数 public  void addActionListener(ActionListener) ，调用该方法可以向按钮增加动作监视器； 

public  void  removeActionListener（ActionListener)调用该方法可以移除按钮上的动作监视器。

  

eg. 如下，求textField1中树的平方显示在textField2中，并且有异常处理

import java.awt.*;
import java.applet.*;
import java.awt.event.*;
 
class  RealizeActionListener  implements    ActionListener
{
    ButtonExample  buttonExample;
    public RealizeActionListener(ButtonExample buttonExample)
    {
        this.buttonExample = buttonExample;
    }
    public void actionPerformed(ActionEvent e)
    {
        try
        {
           double num = Double.valueOf(buttonExample.textField1.getText()).doubleValue();
           num = Math.pow(num, 2);
           buttonExample.textField2.setText(" " + num);
        }
        catch(NumberFormatException event)
        {
           buttonExample.textField2.setText("输入格式不正确！");
        }
    }
}
 
 
public class ButtonExampleextends  Applet
{
    TextField textField1, textField2;
    RealizeActionListener realizeActionListener;
    Button buttonCompute;
    public void init()
    {
        textField1 = new TextField(20);
        textField2 = new TextField(20);
        buttonCompute = new Button("计算平方");
        realizeActionListener = new RealizeActionListener(this);        //监视器类对象
        add(textField1);
        add(textField2);
        add(buttonCompute);
        buttonCompute.addActionListener(realizeActionListener);    //为按钮添加监视器
    }
}

运行结果：