Java：利用GUI实现一个计算器【简易/完整版本】（第十二周）

深碍√TFBOYSˉ_ 2022-05-15 02:39 130阅读 0赞

题目来源：大工慕课 [链接][Link 1]  
作者：Caleb Sung

# 题目要求 #

利用GUI实现一个计算器。点击一个按钮时，显示屏应该显示相应的数字。  
下图为设计样板：  
![70][]  
（MacOS真是随便写个Frame都可以这么好看呀……）

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**注1：本部分结束后，还将贴出教授写的简易版本。这个版本涉及计算的逻辑较为简单，但不能完整正常实现正常计算器的全部功能。此外本文还附有核心Java这本书的随书参考代码，其基于按键响应的编程思路也值得大家借鉴。**  
**注2：电脑端用户可以通过左侧的目录按键快速定位到文章相应位置。**

# 参考解答1（我的版本） #

这道题属于较为综合的题，其中涉及计算的部分涉及了数据结构的相关知识。这部分我讲不做讲解，请自行考察学习。

本篇代码除主函数之外，只有一个类（***类中的方法在下面分别列出***）。下面给出的第一部分代码用于实现计算器的GUI本身：

class CalculatorFrame extends JFrame implements ActionListener { 
    
        String operator = "";
        String input = "";
        boolean flag = true;
        JTextField display = new JTextField("Please input your formula:");
    
        public CalculatorFrame() {
            setTitle("Calculator");
            setVisible(true);
            setDefaultCloseOperation(EXIT_ON_CLOSE);
            setSize(250, 300);
            Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
            setLocation(screenSize.width / 2 - getSize().width / 2, screenSize.height / 2 - getSize().height / 2);
    
            display.setAlignmentY(RIGHT_ALIGNMENT);
            add(display, BorderLayout.NORTH);
    
            JPanel numPad = new JPanel();
            numPad.setLayout(new GridLayout(4, 4));
    
            JButton btnAdd = new JButton("+");
            btnAdd.setForeground(Color.RED);
            btnAdd.addActionListener(this);
    
            JButton btnMinus = new JButton("-");
            btnMinus.setForeground(Color.RED);
            btnMinus.addActionListener(this);
    
            JButton btnTimes = new JButton("*");
            btnTimes.setForeground(Color.RED);
            btnTimes.addActionListener(this);
    
            JButton btnDivision = new JButton("/");
            btnDivision.setForeground(Color.RED);
            btnDivision.addActionListener(this);
    
            JButton btnDot = new JButton(".");
            btnDot.setForeground(Color.RED);
            btnDot.addActionListener(this);
    
            JButton btnEqu = new JButton("=");
            btnEqu.setForeground(Color.RED);
            btnEqu.addActionListener(this);
    
            JButton[] btnNums = new JButton[10];
            for (int i = 0; i < 10; ++i) {
                btnNums[i] = new JButton("" + i);
                btnNums[i].setForeground(Color.BLUE);
                btnNums[i].addActionListener(this);
            }
    
            numPad.add(btnNums[7]);
            numPad.add(btnNums[8]);
            numPad.add(btnNums[9]);
            numPad.add(btnDivision);
            numPad.add(btnNums[4]);
            numPad.add(btnNums[5]);
            numPad.add(btnNums[6]);
            numPad.add(btnTimes);
            numPad.add(btnNums[1]);
            numPad.add(btnNums[2]);
            numPad.add(btnNums[3]);
            numPad.add(btnMinus);
            numPad.add(btnNums[0]);
            numPad.add(btnDot);
            numPad.add(btnEqu);
            numPad.add(btnAdd);
    
            add(numPad, BorderLayout.CENTER);
            validate();
        }
    
        //下续
    }

下面介绍在**CalculatorFrame**类中的两种Method：

## 1. 方法actionPerformed() ##

此方Method用于实现响应按键事件。

public void actionPerformed(ActionEvent e) {
            int cnt = 0;
            String actionCommand = e.getActionCommand();
            if (actionCommand.equals("+") || actionCommand.equals("-") || actionCommand.equals("*")
                    || actionCommand.equals("/"))
                input += " " + actionCommand + " ";
            else if (actionCommand.equals("=")) {
                input += "=" + cmp(input);
                display.setText(input);
                input = "";
                cnt = 1;
            } else
                input += actionCommand;
            if (cnt == 0)
                display.setText(input);
        }

## 2. 方法calc() ##

此Method用于实现执行计算。

private String calc(String input) {
            String str[];
            str = input.split(" ");
            Stack<Double> s = new Stack<Double>();
            double m = Double.parseDouble(str[0]);
            s.push(m);
            for (int i = 1; i < str.length; i++) {
                if (i % 2 == 1) {
                    if (str[i].compareTo("+") == 0) {
                        double help = Double.parseDouble(str[i + 1]);
                        s.push(help);
                    }
    
                    if (str[i].compareTo("-") == 0) {
                        double help = Double.parseDouble(str[i + 1]);
                        s.push(-help);
                    }
    
                    if (str[i].compareTo("*") == 0) {
                        double help = Double.parseDouble(str[i + 1]);
                        double ans = s.peek();//取栈顶
                        s.pop();//消栈
                        ans *= help;
                        s.push(ans);
                    }
    
                    if (str[i].compareTo("/") == 0) {
                        double help = Double.parseDouble(str[i + 1]);
                        double ans = s.peek();
                        s.pop();
                        ans /= help;
                        s.push(ans);
                    }
                }
            }
            double ans = 0;
            while (!s.isEmpty()) {
                ans += s.peek();
                s.pop();
            }
            String result = String.valueOf(ans);
            return result;
        }

--------------------

# 参考解答2（教授简易版本） #

import java.awt.BorderLayout;
    import java.awt.GridLayout;
    import java.awt.event.ActionEvent;
    import java.awt.event.ActionListener;
    
    import javax.swing.*;
    
    /** * A frame with a calculator panel. */
    public class CalculatorFrame extends JFrame { 
        String lastCommand = "=";
        double result = 0;
        JTextField display = new JTextField();
        boolean start = true;
    
        public CalculatorFrame() {
            setTitle("Swing Components");
            setSize(300, 200);
            setDefaultCloseOperation(EXIT_ON_CLOSE);
            setVisible(true);
    
            // Add the display
    
            add(display, BorderLayout.NORTH);
    
            // Define all Buttons
            JButton btnAdd = new JButton("+");
            JButton btnMinus = new JButton("-");
            JButton btnTimes = new JButton("*");
            JButton btnDivision = new JButton("/");
            JButton btnDot = new JButton(".");
            JButton btnEqu = new JButton("=");
    
            btnAdd.addActionListener(new ArithmaticListener());
            btnMinus.addActionListener(new ArithmaticListener());
            btnTimes.addActionListener(new ArithmaticListener());
            btnDivision.addActionListener(new ArithmaticListener());
            btnEqu.addActionListener(new ArithmaticListener());
    
            JButton[] btnNums = new JButton[10];
            for (int i = 0; i < 10; ++i) {
                btnNums[i] = new JButton("" + i);
                btnNums[i].addActionListener(new NumberInputListener());
            }
            btnDot.addActionListener(new NumberInputListener());
    
            // Add the number pad
            JPanel p = new JPanel();
            // Set 4*4 Grid Layout
            p.setLayout(new GridLayout(4, 4));
            p.add(btnNums[7]);
            p.add(btnNums[8]);
            p.add(btnNums[9]);
            p.add(btnDivision);
    
            p.add(btnNums[4]);
            p.add(btnNums[5]);
            p.add(btnNums[6]);
            p.add(btnTimes);
    
            p.add(btnNums[1]);
            p.add(btnNums[2]);
            p.add(btnNums[3]);
            p.add(btnMinus);
    
            p.add(btnNums[0]);
            p.add(btnDot);
            p.add(btnEqu);
            p.add(btnAdd);
            add(p, BorderLayout.CENTER);
            pack();
        }
    
        class NumberInputListener implements ActionListener { 
    
            @Override
            public void actionPerformed(ActionEvent e) {
                String num = e.getActionCommand();
                if (start) {
                    display.setText(num);
                    start = false;
                }
                else
                    display.setText(display.getText()+num);         
            }   
        }
    
        class ArithmaticListener implements ActionListener { 
    
            @Override
            public void actionPerformed(ActionEvent e) {
                start = true;
                String command = e.getActionCommand();
                double x = Double.parseDouble(display.getText());
                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;
                display.setText(""+result);
                lastCommand = command;
            }
        }
    }

--------------------

# 参考解答（核心Java版本的代码） #

## Calculator.java ##

package calculator;
    
    import java.awt.*;
    import javax.swing.*;
    
    /** * @version 1.34 2015-06-12 * @author Cay Horstmann */
    public class Calculator { 
       public static void main(String[] args)
       {
          EventQueue.invokeLater(() -> {
             CalculatorFrame frame = new CalculatorFrame();
             frame.setTitle("Calculator");
             frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
             frame.setVisible(true);
          });
       }
    }

## CalculatorFrame.java ##

package calculator;
    
    import javax.swing.*;
    
    /** * A frame with a calculator panel. */
    public class CalculatorFrame extends JFrame { 
       public CalculatorFrame()
       {
          add(new CalculatorPanel());
          pack();
       }
    }

## CalculatorPanel.java ##

package calculator;
    
    import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;
    
    /** * A panel with calculator buttons and a result display. */
    public class CalculatorPanel extends JPanel { 
       private JButton display;
       private JPanel panel;
       private double result;
       private String lastCommand;
       private boolean start;
    
       public CalculatorPanel()
       {
          setLayout(new BorderLayout());
    
          result = 0;
          lastCommand = "=";
          start = true;
    
          // add the display
    
          display = new JButton("0");
          display.setEnabled(false);
          add(display, BorderLayout.NORTH);
    
          ActionListener insert = new InsertAction();
          ActionListener command = new CommandAction();
    
          // add the buttons in a 4 x 4 grid
    
          panel = new JPanel();
          panel.setLayout(new GridLayout(4, 4));
    
          addButton("7", insert);
          addButton("8", insert);
          addButton("9", insert);
          addButton("/", command);
    
          addButton("4", insert);
          addButton("5", insert);
          addButton("6", insert);
          addButton("*", command);
    
          addButton("1", insert);
          addButton("2", insert);
          addButton("3", insert);
          addButton("-", command);
    
          addButton("0", insert);
          addButton(".", insert);
          addButton("=", command);
          addButton("+", command);
    
          add(panel, BorderLayout.CENTER);
       }
    
       /** * Adds a button to the center panel. * @param label the button label * @param listener the button listener */
       private void addButton(String label, ActionListener listener)
       {
          JButton button = new JButton(label);
          button.addActionListener(listener);
          panel.add(button);
       }
    
       /** * This action inserts the button action string to the end of the display text. */
       private class InsertAction implements ActionListener { 
          public void actionPerformed(ActionEvent event)
          {
             String input = event.getActionCommand();
             if (start)
             {
                display.setText("");
                start = false;
             }
             display.setText(display.getText() + input);
          }
       }
    
       /** * This action executes the command that the button action string denotes. */
       private class CommandAction implements ActionListener { 
          public void actionPerformed(ActionEvent event)
          {
             String command = event.getActionCommand();
    
             if (start)
             {
                if (command.equals("-"))
                {
                   display.setText(command);
                   start = false;
                }
                else lastCommand = command;
             }
             else
             {
                calculate(Double.parseDouble(display.getText()));
                lastCommand = command;
                start = true;
             }
          }
       }
    
       /** * Carries out the pending calculation. * @param x the value to be accumulated with the prior result. */
       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;
          display.setText("" + result);
       }
    }

--------------------

# 运行效果 #

![这里写图片描述][70 1]

[Link 1]: https://mooc.dlut.edu.cn/
[70]: /images/20220515/4727362f31984fa684bf25e7ab7e8b2f.png
[70 1]: /images/20220515/b583ff8f1e804c2b8dc66994702bf431.png