btnevt_ca.java

java练习程序

import java.applet.*;
import java.awt.*;
import java.awt.event.*;

public class BtnEvt_Ca extends Applet implements ActionListener
{
  TextField text1,text2,text3;
  Button Btn1,Btn2,Btn3,Btn4;
  public void init()
  {
  	text1=new TextField(10);
  	text2=new TextField(10);
  	text3=new TextField(10);
  	add(text1);
  	add(text2);
  	add(text3);

  	Btn1=new Button("加");
  	Btn2=new Button("减");
  	Btn3=new Button("乘");
  	Btn4=new Button("除");
  	add(Btn1);
  	add(Btn2);
  	add(Btn3);
  	add(Btn4);
  	Btn1.addActionListener(this);
  	Btn2.addActionListener(this);
  	Btn3.addActionListener(this);
  	Btn4.addActionListener(this);
  }
  public void paint(Graphics g)
  {
  	g.drawString("在左边第一、二个文本框中输入数字，再单击相应的按钮",
  		10,100);
  	g.drawString("第三个文本框显示运算结果",10,120);
  }
  public void actionPerformed(ActionEvent e)
  {
  	double n;
  	if(e.getSource()==Btn1)
  	{
  		double n1,n2;
  		n1=Double.valueOf(text1.getText()).doubleValue();
  		n2=Double.valueOf(text2.getText()).doubleValue();
  		n=n1+n2;
  		text3.setText(String.valueOf(n));
  	}else if(e.getSource()==Btn2)
  	{
  		double n1,n2;
  		n1=Double.valueOf(text1.getText()).doubleValue();
  		n2=Double.valueOf(text2.getText()).doubleValue();
  		n=n1-n2;
  		text3.setText(String.valueOf(n));
  	}else if(e.getSource()==Btn3)
  	{
  		double n1,n2;
  		n1=Double.valueOf(text1.getText()).doubleValue();
  		n2=Double.valueOf(text2.getText()).doubleValue();
  		n=n1*n2;
  		text3.setText(String.valueOf(n));
  	}else if(e.getSource()==Btn4)
  	{
  		double n1,n2;
  		n1=Double.valueOf(text1.getText()).doubleValue();
  		n2=Double.valueOf(text2.getText()).doubleValue();
  		n=n1/n2;
  		text3.setText(String.valueOf(n));
  	}
  }

}
/*
public class ch8_1 extends Applet
{
  
  String s;
  public void init()
  {
  	text1=new TextField(10);
  	text1.setEditable(false);
  	text2=new TextField(10);
//  	text2.setEchoChar('*'); 	
  	text3=new TextField("文本框",20);
  	
  	add(text1);
  	add(text2);
  	add(text3);
  	s=text2.getText();
  	text3.setText(s);
  }
}
*/