小型计算器

使用Java语言编写一个小型运算器，可以实现四则运算。

import java.awt.BorderLayout;
import java.awt.Button;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class Calculator extends JFrame{
    //声明一个文本栏控件，用于显示计算结果
    private JTextField txtResult;
    private JPanel p;
    //定义一个字符串数组，将计算器中按钮的文字都放在该数组中
    private String name[]={
            "7","8","9","+","4","5","6","-",
            "1","2","3","*","0",".","=","/"};
    //声明一个按钮数组，该数组的长度以字符串数组的长度为准
    private JButton button[]=new JButton[name.length];
    //定义一个存放计算结果的变量，初始为0
    private double result=0;
    //存放最后一个操作符，初始为“=”
    private String lastCommand="=";
    //标识是否开始
    private boolean start =true;
    public Calculator(){
        super("计算器");
        //实例化文本栏控件
        txtResult=new JTextField(20);
        //设置文本框不是焦点状态
        txtResult.setFocusable(false);
        //将文本栏控件放置在窗体框架的上方（北部）
        this.add(txtResult,BorderLayout.NORTH);
        //实例化面板对象，同时设置此面板布局为4行4列的网格布局
        p=new JPanel(new GridLayout(4,4));
        /**
         * 循环实例化按钮对象数组
         * 实例化按钮监听对象
         */
        ButtonAction ba=new ButtonAction();
        //实例化键盘监听对象
        KeyAction ka=new KeyAction();
        for(int i=0;i<button.length;i++){
            button[i]=new JButton(name[i]);
            //注册监听
            button[i].addActionListener(ba);
            button[i].addKeyListener(ka);
            p.add(button[i]);
        }
        this.add(p,BorderLayout.CENTER);
        //设定窗口大小
        this.setSize(200,200);
        //设定窗口左上角坐标
        this.setLocation(200, 100);
        //设定窗口默认关闭方式为退出应用程序
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        //设定窗口可视
        this.setVisible(true);
    }
    //计算
    public void calculate(double x){
        if(lastCommand.equals("+"))
            result +=x;
        else if(lastCommand.equals("-"))
            result -=x;
        else if(lastCommand.equals("*"))
            result *=x;
        else if(lastCommand.equals("/"))
            result /=x;
        else if(lastCommand.equals("="))
            result =x;
        //将结果显示在文本栏
        txtResult.setText(""+result);
                
    }
    //单击按钮监听
    private class ButtonAction implements ActionListener{
        public void actionPerformed(ActionEvent e){
            String input =e.getActionCommand();
            //单击操作符号按钮
            if(input.equals("+")||input.equals("-")||input.equals("*")
                    ||input.equals("/")||input.equals("=")){
                if(start){
                    if(input.equals("-")){
                        txtResult.setText(input);
                        start=false;
                    }else
                        lastCommand=input;
                }else{
                    calculate(Double.parseDouble(txtResult.getText()));
                    lastCommand=input;
                    start=true;
                }
            }else{
                if(start){
                    txtResult.setText("");
                    start=false;
                }
                txtResult.setText(txtResult.getText()+input);
            }
            }
        }
    //键盘监听
    private class KeyAction extends KeyAdapter{
        public void KeyTyped(KeyEvent e){
            char key=e.getKeyChar();
            //敲击的键盘是数字
            if(key=='0'||key=='1'||key=='2'||key=='3'||key=='4'
                    ||key=='5'||key=='6'||key=='7'||key=='8'
                    ||key=='9'){
                if(start){
                    txtResult.setText("");
                    start=false;
                }
                txtResult.setText(txtResult.getText()+ key);
            }
            //敲击的是操作符号
            else if(key=='+'||key=='-'||key=='*'||key=='/'
                    ||key=='='){
                if(start){
                    if(key=='-'){
                        txtResult.setText(String.valueOf(key));
                        start=false;
                    }else
                        lastCommand=String.valueOf(key);
                }else{
                    calculate(Double.parseDouble(txtResult.getText()));
                    lastCommand=String.valueOf(key);
                    start=true;
                }
            }
        }
    }
    public static void main(String[] args){
        new Calculator();
    }
    }