Java：利用GUI实现一个计算器【简易/完整版本】（第十二周）

版权声明：根据《中华人民共和国著作权法》，如需转载请标明来源并联系作者进行授权。本文作者保留依法追究未经授权转载等侵犯作者著作权等的违法行为之权利。 https://blog.csdn.net/qq_41933331/article/details/81982594

题目来源：大工慕课 链接
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：

（MacOS真是随便写个Frame都可以这么好看呀……）

---

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