Java如何实现一个简单计算器

package test1;
 
import java.awt.Frame;
import java.awt.TextField;
import java.awt.Button;
import java.awt.Panel;
import java.awt.GridLayout;
 
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
 
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class calculate {
    TextField tfResult;
    Button btNum[],btOper[],btPoint,btEqual,btBack,btSqrt,btPingfang,btLifang;
    int num1,num2;//操作数
    char oper;//操作符
    boolean isNum;//代表数字标志位
    public void init(){
        Frame f;
        
        tfResult=new TextField();
        
        btNum=new Button[10];//数组对象
        for(int i=0;i<=9;i++){
            btNum[i]=new Button(i+"");
        }
        btOper=new Button[4];
        btOper[0]=new Button("+");
        btOper[1]=new Button("-");
        btOper[2]=new Button("*");
        btOper[3]=new Button("/");
        
        btPoint=new Button(".");
        btEqual=new Button("=");
        btBack=new Button("Backspace");
        btSqrt=new Button("Sqrt");
        btPingfang=new Button("2");
        btLifang=new Button("3");
        f=new Frame("小羊羔的计算器！");
        
        f.setSize(300,300);
        
        //放置组件
        f.add(tfResult,"North");
        Panel panel=new Panel();
        f.add(panel,"Center");
        GridLayout gl=new GridLayout(5,4);
        panel.setLayout(gl);
        panel.add(btNum[1]);
        panel.add(btNum[2]);
        panel.add(btNum[3]);
        panel.add(btOper[0]);
        
        panel.add(btNum[4]);
        panel.add(btNum[5]);
        panel.add(btNum[6]);
        panel.add(btOper[1]);
        
        panel.add(btNum[7]);
        panel.add(btNum[8]);
        panel.add(btNum[9]);
        panel.add(btOper[2]);
        
        panel.add(btNum[0]);
        panel.add(btPoint);
        panel.add(btEqual);
        panel.add(btOper[3]);
        
        panel.add(btBack);
        panel.add(btSqrt);
        panel.add(btPingfang);
        panel.add(btLifang);
        f.setVisible(true);
        
        //注册监听
        f.addWindowListener(new MyWinLis());
        //数字按钮注册监听
        MyNumLis mnl=new MyNumLis();
        for(int i=0;i<=9;i++)
            btNum[i].addActionListener(mnl);
        
        //操作符按钮注册监听
        MyOperLis mol=new MyOperLis();
        for(int j=0;j<=3;j++)
            btOper[j].addActionListener(mol);
        //等号按钮注册监听
        MyEqualLis mel=new MyEqualLis();
        btEqual.addActionListener(mel);
        //删除按钮注册监听
        MyBackLis mbl=new MyBackLis();
        btBack.addActionListener(mbl);
        //开根号按钮注册监听
        MySqrtLis msl=new MySqrtLis();
        btSqrt.addActionListener(msl);
        //平方按钮注册监听
        MyPingfangLis mpl=new MyPingfangLis();
        btPingfang.addActionListener(mpl);
        //百分号注册监听
        MyLifangLis mll=new MyLifangLis();
        btLifang.addActionListener(mll);
    }
    //定义监听器类
    class MyNumLis implements ActionListener{
        public void actionPerformed(ActionEvent e){
            String t=e.getActionCommand();
            String s=tfResult.getText();
            if(isNum==false)
                tfResult.setText(t);
            else 
                tfResult.setText(s+t);
            isNum=true;
        }
    }
    class MySqrtLis implements ActionListener{
        public void actionPerformed(ActionEvent e){
            double t=Double.parseDouble(tfResult.getText());
            tfResult.setText(Math.sqrt(t)+"");
            isNum=false;
        }
    }
    class MyPingfangLis implements ActionListener{
        public void actionPerformed(ActionEvent e){
            num1=Integer.parseInt(tfResult.getText());
            tfResult.setText(num1*num1+"");
        }
    }
    class MyLifangLis implements ActionListener{
        public void actionPerformed(ActionEvent e){
            num1=Integer.parseInt(tfResult.getText());
            tfResult.setText(num1*num1*num1+"");
        }
    }
    class MyOperLis implements ActionListener{
        public void actionPerformed(ActionEvent e){
            num1=Integer.parseInt(tfResult.getText());//转化为INT
            oper=e.getActionCommand().charAt(0);
            isNum=false;
        }
    }
    class MyEqualLis implements ActionListener{
        public void actionPerformed(ActionEvent e){
            int result=0;
            isNum=false;
            num2=Integer.parseInt(tfResult.getText());
            switch(oper){
                case '+':result=num1+num2;break;
                case '-':result=num1-num2;break;
                case '*':result=num1*num2;break;
                case '/':result=num1/num2;break;
            }
            tfResult.setText(result+"");
        }
    }
    class MyBackLis implements ActionListener{
        public void actionPerformed(ActionEvent e){
            tfResult.setText("");
            isNum=false;
        }
    }
    class MyWinLis extends WindowAdapter{
        public void windowClosing(WindowEvent e){
            e.getWindow().setVisible(false);
            e.getWindow().dispose();
            System.exit(0);
        }
    }
    
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        new calculate().init();
    }
 
}