按钮事件处理程序

import java.awt.*;import java.awt.event.*;import java.applet.*;public class ButtonDemo extends Applet implements ActionListener{String msg=" ";//定义按钮“是”、“否”、“取消”public void init(){Button yes =new Button("是");Button no=new Button("否");Button maybe=new Button("取消");add(yes);add(no);add(maybe);yes.addActionListener(this);no.addActionListener(this);maybe.addActionListener(this);}public void actionPerformed(ActionEvent e){String str=e.getActionCommand();if(str=="是"){msg="您单击了按钮'是'。";}else if(str=="否"){msg="您单击了按钮'否'。";}else{msg="您单击了按钮'取消'。";}repaint();}public void paint(Graphics g){g.drawString(msg, 6, 100);}}