calculator.java

Java 图形界面入门实例

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

public class Calculator extends Applet implements ActionListener 
{
    private TextField display ;
    private double arg=0 ;
    private String op="=" ;
    private boolean start=true ;
    
    public void init()
    {
        setLayout(new BorderLayout());
        display=new TextField("0");
        display.setEditable(true);
        add(display,"North");
        
        Panel p=new Panel();
        p.setLayout(new GridLayout(4,4));
        String buttons="123+456-789*0.=/" ;
        for(int i=0;i<buttons.length();i++)
        {
            Button b=new Button(buttons.substring(i,i+1));
            p.add(b);
            b.addActionListener(this);
        }
        add(p,"Center");
    }
    
    public void actionPerformed(ActionEvent ev)
    {
        String s=ev.getActionCommand();
        if('0'<=s.charAt(0) && s.charAt(0)<='9' || s.equals("."))
        {
            if(start)
            display.setText(s);
            else 
            display.setText(display.getText()+s);
            start=false ;
        }
        else 
        {
            if(start)
            {
                if(s.equals("-"))
                {
                    display.setText(s);
                    start=false ;
                }
                else 
                op=s ;
             }
             else
             {
                    calculate(Double.parseDouble(display.getText()));
                    op=s ;
                    start=true ;
             }
            }
        }
        
        public void calculate(double n)
        {
            if(op.equals("+"))
            arg+=n ;
            else if(op.equals("-"))
            arg-=n ;
            else if(op.equals("*"))
            arg*=n ;
            else if(op.equals("/"))
            arg/=n ;
            else if(op.equals("="))
            arg=n ;
            display.setText(Double.toString(arg));
        }
    }