一、界面布局：

1.首先，由于計算器分為顯示框和按鈕，所以我們選用BorderLayout邊界布局；
2.窗體中放置三個JPanel面板，第一個面板放文本框，置于頂部；第二個面板放“清零”（AC）按鈕與“退格”按鈕，置于中部。第三個面板放數(shù)字與操作符組件（0-9，+ - * / . =），4*4網(wǎng)格布局，置于窗體底部；

(1)定義面板，文本框和按鈕組件：

JPanel top;
JPanel center;
JPanel botton;
JTextField xianshi;
JButton ac;
JButton tuige;
JButton bt1;
JButton bt2;
JButton bt3;
JButton bt4;
JButton bt5;
JButton bt6;
JButton bt7;
JButton bt8;
JButton bt9;
JButton bt0;
JButton dian;
JButton jia;
JButton jian;
JButton cheng;
JButton chu;
JButton dengyu;

(2)頂部布局

//繪制頂部布局（文本框）
        BorderLayout borderLayout=new BorderLayout();
        top=new JPanel();       
        add(top,BorderLayout.NORTH);        
        GridLayout t=new GridLayout();  
        top.setLayout(t);
        xianshi=new JTextField();
        top.add(xianshi);

(3)中部布局

//繪制中部布局（退格和歸零兩個按鈕）
        center=new JPanel();
        add(center,BorderLayout.CENTER);
        GridLayout c=new GridLayout(1,2,5,5);   
        center.setLayout(c);
        ac=new JButton("AC");
        tuige=new JButton("退格");
        center.add(ac);
        center.add(tuige);

(4)底部布局

//繪制底部布局（4*4的網(wǎng)格放一堆按鈕）

        botton=new JPanel();
        add(botton,BorderLayout.SOUTH);
        GridLayout b=new GridLayout(4,4,5,5);
        botton.setLayout(b);
        
        bt1=new JButton("1");   
        bt2=new JButton("2");
        bt3=new JButton("3");
        jia=new JButton("+");
        bt4=new JButton("4");
        bt5=new JButton("5");
        bt6=new JButton("6");
        jian=new JButton("-");
        bt7=new JButton("7");
        bt8=new JButton("8");
        bt9=new JButton("9");
        cheng=new JButton("*");
        bt0=new JButton("0");
        dian=new JButton(".");
        chu=new JButton("/");
        dengyu=new JButton("=");

(5)添加按鈕到底部面板

        botton.add(bt1);
        botton.add(bt2);
        botton.add(bt3);
        botton.add(jia);
        botton.add(bt4);
        botton.add(bt5);        
        botton.add(bt6);        
        botton.add(jian);       
        botton.add(bt7);        
        botton.add(bt8);        
        botton.add(bt9);        
        botton.add(cheng);      
        botton.add(bt0);        
        botton.add(dian);       
        botton.add(chu);        
        botton.add(dengyu);

二、添加監(jiān)聽器
1.首先，我們需要兩個監(jiān)聽器，第一個監(jiān)聽器用來監(jiān)聽0-9數(shù)字鍵，為數(shù)字監(jiān)聽器；另一個監(jiān)聽器用來監(jiān)聽加減乘除按鈕，為功能監(jiān)聽器。
2.我們需要立一個flag，且令flag初始值為true，以便于我們重啟計算器。

(1).創(chuàng)建數(shù)字監(jiān)聽器Listener1：

 class Listener1 implements ActionListener{

            @Override
            public void actionPerformed(ActionEvent e) {
                // TODO Auto-generated method stub
                String dianji = e.getActionCommand();//獲得點擊的按鈕
                if(flag) {
                    xianshi.setText("");
                    flag=false;
                }if(!dianji.equals("退格")){
                    xianshi.setText(xianshi.getText()+dianji);
                }if(dianji.equals("AC")) {
                    xianshi.setText("0");
                    flag=true;
            
                }if(dianji.equals("退格")) {
                    if(xianshi.getText().length()>1) {
                        xianshi.setText(xianshi.getText().substring(0,xianshi.getText().length()-1));
                        //字符串長度減1
                    }else {
                        xianshi.setText("0");
                    }if(xianshi.getText().equals("0")) {
                        flag=true;//當(dāng)文本框顯示0的時候，重啟
                    }
                    
                }if(dianji.equals(".")) {
                
                }
            }
         }

(2).創(chuàng)建功能監(jiān)聽器Listener2

 class Listener2 implements ActionListener{

        @Override
        public void actionPerformed(ActionEvent e) {
            // TODO Auto-generated method stub
            String dianji = e.getActionCommand();
            if(flag){
                fuhao=dianji;
            }else {
                if(fuhao.equals("+")) {
                    
                    result += Double.parseDouble(xianshi.getText());//字符串轉(zhuǎn)double                    
                }if(fuhao.equals("-")) {
                    result -= Double.parseDouble(xianshi.getText());
                }if(fuhao.equals("*")) {
                    result *= Double.parseDouble(xianshi.getText());
                }if(fuhao.equals("/")) {
                    result /= Double.parseDouble(xianshi.getText());
                }if(fuhao.equals("=")) {
                    result = Double.parseDouble(xianshi.getText());
                }
                xianshi.setText(""+result);
                fuhao=dianji;
                flag=true;
            }
        }
         
     }

三、代碼效果圖：

計算器.png

四、完整代碼如下:

package jiemian;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;


import javax.swing.*;
public class JSQ extends JFrame {
    public static void main(String[] args) {
        JSQ frame=new JSQ();
        frame.setSize(350,250);
        frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
        frame.setVisible(true);

        }
    JPanel top;
    JPanel center;
    JPanel botton;
    JTextField xianshi;
    JButton ac;
    JButton tuige;

    
    JButton bt1;
    JButton bt2;
    JButton bt3;
    JButton bt4;
    JButton bt5;
    JButton bt6;
    JButton bt7;
    JButton bt8;
    JButton bt9;
    JButton bt0;
    JButton dian;   
    JButton jia;
    JButton jian;
    JButton cheng;
    JButton chu;
    JButton dengyu;

    
    
    
    Listener1 a1;
    Listener2 a2;
    boolean flag;//定義運算開始標(biāo)志
    
    double result;//定義result接收運算結(jié)果
    String fuhao;//定義fuhao接收符號
    
    public JSQ() {
        fuhao="=";
        result=0;
        flag=true;
        this.setTitle("小王計算器");
        
        //繪制頂部布局（文本框）
        BorderLayout borderLayout=new BorderLayout();
        top=new JPanel();       
        add(top,BorderLayout.NORTH);        
        GridLayout t=new GridLayout();  
        top.setLayout(t);
        xianshi=new JTextField();
        top.add(xianshi);
        

        //繪制中部布局（退格和歸零兩個按鈕）
        center=new JPanel();
        add(center,BorderLayout.CENTER);
        GridLayout c=new GridLayout(1,2,5,5);   
        center.setLayout(c);
        ac=new JButton("AC");
        tuige=new JButton("退格");
        center.add(ac);
        center.add(tuige);
        
        
        
        //繪制底部布局（4*4的網(wǎng)格放一堆按鈕）
        botton=new JPanel();
        add(botton,BorderLayout.SOUTH);
        GridLayout b=new GridLayout(4,4,5,5);
        botton.setLayout(b);
        
        bt1=new JButton("1");   
        bt2=new JButton("2");
        bt3=new JButton("3");
        jia=new JButton("+");
        bt4=new JButton("4");
        bt5=new JButton("5");
        bt6=new JButton("6");
        jian=new JButton("-");
        bt7=new JButton("7");
        bt8=new JButton("8");
        bt9=new JButton("9");
        cheng=new JButton("*");
        bt0=new JButton("0");
        dian=new JButton(".");
        chu=new JButton("/");
        dengyu=new JButton("=");
        
        a1=new Listener1();
        a2=new Listener2();
        
        
        //添加按鈕到底部面板
        botton.add(bt1);
        botton.add(bt2);
        botton.add(bt3);
        botton.add(jia);
        botton.add(bt4);
        botton.add(bt5);        
        botton.add(bt6);        
        botton.add(jian);       
        botton.add(bt7);        
        botton.add(bt8);        
        botton.add(bt9);        
        botton.add(cheng);      
        botton.add(bt0);        
        botton.add(dian);       
        botton.add(chu);        
        botton.add(dengyu);
        
        
        //按鈕全部加上監(jiān)聽器（a1為數(shù)字監(jiān)聽器，a2為運算符號的功能監(jiān)聽器）
        bt1.addActionListener(a1);
        bt2.addActionListener(a1);
        bt3.addActionListener(a1);
        jia.addActionListener(a2);
        bt4.addActionListener(a1);
        bt5.addActionListener(a1);
        bt6.addActionListener(a1);
        jian.addActionListener(a2);
        bt7.addActionListener(a1);
        bt8.addActionListener(a1);
        bt9.addActionListener(a1);
        cheng.addActionListener(a2);
        bt0.addActionListener(a1);
        dian.addActionListener(a1);
        chu.addActionListener(a2);
        dengyu.addActionListener(a2);
        tuige.addActionListener(a1);
        ac.addActionListener(a1);

        
    }
    
      
     class Listener1 implements ActionListener{

            @Override
            public void actionPerformed(ActionEvent e) {
                // TODO Auto-generated method stub
                String dianji = e.getActionCommand();//獲得點擊的按鈕
                if(flag) {
                    xianshi.setText("");
                    flag=false;
                }if(!dianji.equals("退格")){
                    xianshi.setText(xianshi.getText()+dianji);
                }if(dianji.equals("AC")) {
                    xianshi.setText("0");
                    flag=true;
            
                }if(dianji.equals("退格")) {
                    if(xianshi.getText().length()>1) {
                        xianshi.setText(xianshi.getText().substring(0,xianshi.getText().length()-1));
                        //字符串長度減1
                    }else {
                        xianshi.setText("0");
                    }if(xianshi.getText().equals("0")) {
                        flag=true;//當(dāng)文本框顯示0的時候，重啟
                    }
                    
                }if(dianji.equals(".")) {
                
                }
            }
         }
     class Listener2 implements ActionListener{

        @Override
        public void actionPerformed(ActionEvent e) {
            // TODO Auto-generated method stub
            String dianji = e.getActionCommand();
            if(flag){
                fuhao=dianji;
            }else {
                if(fuhao.equals("+")) {
                    
                    result += Double.parseDouble(xianshi.getText());//字符串轉(zhuǎn)double                    
                }if(fuhao.equals("-")) {
                    result -= Double.parseDouble(xianshi.getText());
                }if(fuhao.equals("*")) {
                    result *= Double.parseDouble(xianshi.getText());
                }if(fuhao.equals("/")) {
                    result /= Double.parseDouble(xianshi.getText());
                }if(fuhao.equals("=")) {
                    result = Double.parseDouble(xianshi.getText());
                }
                xianshi.setText(""+result);
                fuhao=dianji;
                flag=true;
            }
        }
         
     }
    
     }