floataddapp.java

java程序设计 清华出版社 孙燮华老师编写的程序源代码

//floatAddApp.java, Author Xie-Hua Sun, 2001.03.16
import java.lang.*;
import java.awt.*;
import java.awt.event.*;

public class floatAddApp extends Frame implements ActionListener{
  TextField text1,text2,answertext;
  Label pluslabel;
  Button button1;
	  
  public floatAddApp(){
    setLayout(new FlowLayout());      
    text1=new TextField(10);
    pluslabel=new Label("+",Label.CENTER);//put "+" in center
    text2=new TextField(10);
    button1=new Button("=");
    button1.addActionListener(this);
    answertext=new TextField(10);
    add(text1);
    add(pluslabel);
    add(text2);
    add(button1);
    add(answertext);
    setSize(250,100);
    setVisible(true);
  }
      
  public void actionPerformed(ActionEvent e){
    if(e.getSource()==button1){
      Float f1=Float.valueOf(text1.getText());
      Float f2=Float.valueOf(text2.getText());
      floatAdd adder=new floatAdd();//create an object for adding floats
      float sum=adder.add(f1,f2);   //add two Floats
      answertext.setText(String.valueOf(sum));
    }
  }

  public static void main(String args[]){
    floatAddApp myAdd=new floatAddApp();        
  }
}

//扩展接口addTool
class floatAdd implements addTool{
  public float add(Object x1,Object x2){ //add two values
    if((x1 instanceof Float)&&(x2 instanceof Float)){
      float f1=((Float)x1).floatValue();
      float f2=((Float)x2).floatValue();
      return(f1+f2);
    }
    else throw addTool.err1;    
  }
}