Java程序编写一个计算器类，要求实现加、减、乘、除运算，注意在进行除法运算时，如果除数为0，

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Caculator extends JFrame implements KeyListener{ //构造Caculator类
private Container content;//构造容器
private JButton bCancel;  //清除按钮
private JButton[] b=new JButton[16];  //构造按钮数组
private char LastOp;   //操作符号
private boolean Countable;   //用于判断是否可计算
private String KeyLabel[]={"7","8","9","/","4","5","6","*","1","2","3","-","0",".","=","+"};
private StringBuffer str;
private JPanel KeyPanel,TextPanel;  //按键面板，结果面板
private JTextArea tResult; //用于显示结果的文本域
private double x=0,y=0; //操作数
 public Caculator(){
     setTitle("袖珍计算器");
     setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     content =getContentPane(); //初始化一个容器
     content.setLayout(new BorderLayout());    //设置容器的布局方式
     KeyPanel=new JPanel(); 
     TextPanel=new JPanel();
     TextPanel.setLayout(new FlowLayout());     //设置TextPanel面板的布局方式
     KeyPanel.setLayout(new GridLayout(4,4));   //设置KeyPanel面板的布局方式
    tResult=new JTextArea(1,15);    //实例化一个JTextArea类
    tResult.setEditable(false);     //将tResult设置为不可编辑
    tResult.setText("0");           //文本域显示为0
    tResult.addKeyListener(this);   //添加键盘监听器
    str=new StringBuffer();         //实例化一个字符串缓冲区
       
    ButtonListener btnListener = new ButtonListener();   //实例化一个ButtonListener类的监听器
    for(int i=0;i<16;i++){
     b[i] = new JButton(KeyLabel[i]);
     b[i].addActionListener(btnListener);  //添加ButtonListener类监听器
     b[i].addKeyListener(this);   //添加键盘监听器
     KeyPanel.add(b[i]);
   } 
    bCancel=new JButton("C");   
    bCancel.addActionListener(btnListener);  //添加ButtonListener类监听器
    bCancel.addKeyListener(this);            //添加键盘监听器
    bCancel.setBackground(Color.RED);
    LastOp='!';    //若LastOp的值不为'+' '-' '*' '/'中的一个，则约定它的值是 '!'
    Countable=false;
         
   TextPanel.add(tResult);
   TextPanel.add(bCancel);
   content.add("North",TextPanel);
   content.add("Center",KeyPanel);
   pack();
   setResizable(false);
   setVisible(true);  
 }
 class ButtonListener implements ActionListener  //构造监听器
 {
 public void actionPerformed(ActionEvent e) {
         String s = ((JButton)e.getSource()).getText().trim(); //得到用户按下的按钮上的文本
         char c = s.charAt(0);       //得到s中索引为0的字符
              
     if(c == 'C')         //选择按钮C
     {
      tResult.setText("0");
      str.setLength(0);
      LastOp = '!';
      Countable = false;
      x = 0;
      y = 0;
      return;
     }
        
       
    if(c == '.')  //选择输入小数点
    {
      if( tResult.getText().trim().indexOf(".") != -1) return;
      else
      { str.insert(str.length(),".");
        tResult.append(".");
        return;
      }
    }
    if(c == '+'||c ==  '-'||c == '*'||c == '/'||c == '=')     //按加减乘除或等号键
    {
     Caculate(c);
     return;
    }     
      
//剩下的数字键
    tResult.setText(str.append(s).toString());
    Countable=true;
 }
 }
      
 //实现KeyListener监听器
 public void keyTyped(KeyEvent ek)
 {
  char c = ek.getKeyChar();      //获取键盘上按的数字键
 if(c=='1'||c=='2'||c=='3'||c=='4'||c=='5'||c=='6'||c=='7'||c=='8'||c=='9'||c=='0')
  {
   tResult.setText(str.append(c).toString());
   Countable=true;
   return;
  }
  if(c =='.')             //按小数点
  {
     if( tResult.getText().trim().indexOf(".") != -1) return;
     else
     { str.insert(str.length(),".");
       tResult.append(".");
       return;
     }
   }
        
  if((int)c == KeyEvent.VK_DELETE )   //按delete键
    {
         tResult.setText("0");
          str.setLength(0);
          LastOp = '!';
          Countable = false;
          x = 0;
          y = 0;
          return;
   }
  if(c == '+'||c ==  '-'||c == '*'||c == '/'||c == '=')            //按加减乘除或等号键
  {
   Caculate(c);
   return;
  }     
}
 public void keyPressed(KeyEvent ek) {}
 public void keyReleased(KeyEvent ek) {}
 public void Caculate(char c)
 {
     if(c == '+')            //按加号键
      {
       Add();
       return;
      }     
             
     if( c == '-')          //按减号键
      {
       Minus();
       return;
      }     
     if(c  == '*')             //按乘号键
     {
     Mul();
     return;
      } 
      if(c == '/')             //按除号键
      {
     Div();
     return;
      }
      if(c == '=')       //按等号键
      {
     Equal();
     return;
     }
 }
 public void Add(){          //加方法
      if(Countable==true && LastOp != '!')   //判断是否进行运算
        { 
        y = Double.parseDouble(tResult.getText().trim());
        switch(LastOp)
        {
       case '+' : x = x+y;  break;
        case '-' : x = x-y;  break;
        case '*' : x = x*y;  break;
        case '/' :if(y != 0)  x = x/y;  
                 else
                 {
                   tResult.setText("除数不能为0");return;
                  }
        }       
        tResult.setText(""+x);   
        Countable = false;
       }
       else  x = Double.parseDouble(tResult.getText().trim());
       str.setLength(0);
       y = 0;
       LastOp = '+';  
        return ;  
 }
 public void Minus(){       //减方法
      if(Countable==true && LastOp != '!')      //判断是否进行运算
        { 
        y = Double.parseDouble(tResult.getText().trim());
        switch(LastOp)
        {
       case '+' : x = x+y;  break;
        case '-' : x = x-y;  break;
        case '*' : x = x*y;  break;
        case '/' :if(y != 0)  x = x/y;     
                 else
                 {
                   tResult.setText("除数不能为0");return;
                  }
        }
        tResult.setText(""+x);   
        Countable = false;
       }
       else  x = Double.parseDouble(tResult.getText().trim());
       str.setLength(0);
       y = 0;
       LastOp = '-';  
       return ; 
 }
 public void Mul(){    //乘方法
     if(Countable==true && LastOp != '!')     //判断是否进行运算
        { 
        y = Double.parseDouble(tResult.getText().trim());
        switch(LastOp)
        {
       case '+' : x = x+y;  break;
        case '-' : x = x-y;  break;
        case '*' : x = x*y;  break;
        case '/' :if(y != 0)  x = x/y;  
                 else
                 {
                   tResult.setText("除数不能为0");return;
                  }
         }
        tResult.setText(""+x);   
        Countable = false;
       }
       else  x = Double.parseDouble(tResult.getText().trim());
       str.setLength(0);
       y = 0;
       LastOp = '*';  
       return ; 
 }
 public void Div()  //除方法
 {
     if(Countable==true && LastOp != '!')          //判断是否进行运算
        { 
        y = Double.parseDouble(tResult.getText().trim());
        switch(LastOp)
        {
       case '+' : x = x+y;  break;
        case '-' : x = x-y;  break;
        case '*' : x = x*y;  break;
        case '/' :if(y != 0)  x = x/y;  
                else
                {
                 tResult.setText("除数不能为0");return;
                }
        }       
        tResult.setText(""+x);   
        Countable = false;
       }
       else  x = Double.parseDouble(tResult.getText().trim());
       str.setLength(0);
       y = 0;
       LastOp = '/';  
       return ; 
 }
 public void Equal()   //求结果的方法
 {
       y = Double.parseDouble(tResult.getText().trim());
        switch(LastOp)
        {
       case '+' : x = x+y;  break;
        case '-' : x = x-y;  break;
        case '*' : x = x*y;  break;
        case '/' :if(y != 0)  x = x/y;  
                 else
                 {
                   tResult.setText("除数不能为0");return;
                  }
       }
        tResult.setText(""+x);
        Countable=false;
        return;
 }
 public static void main(String args[])
 {
    Caculator cal=new Caculator();
 }
}

用Java定义一个类，实现加减乘除计算功能，把结果输出？