Java：利用GUI实现一个计算器【简易/完整版本】（第十二周）

Java：利用GUI实现一个计算器【简易/完整版本】（第十二周）

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 = DefaultToolkit().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;} elseinput += 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]pareTo("+") == 0) {double help = Double.parseDouble(str[i + 1]);s.push(help);}if (str[i]pareTo("-") == 0) {double help = Double.parseDouble(str[i + 1]);s.push(-help);}if (str[i]pareTo("*") == 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]pareTo("/") == 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 displayadd(display, BorderLayout.NORTH);// Define all ButtonsJButton 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 padJPanel p = new JPanel();// Set 4*4 Grid Layoutp.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 {@Overridepublic void actionPerformed(ActionEvent e) {String num = e.getActionCommand();if (start) {display.setText(num);start = false;}elsedisplay.Text()+num);         }   }class ArithmaticListener implements ActionListener {@Overridepublic void actionPerformed(ActionEvent e) {start = true;String command = e.getActionCommand();double x = Double.Text());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 displaydisplay = 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 gridpanel = 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 = ActionCommand();if (start){display.setText("");start = false;}display.Text() + input);}}/*** This action executes the command that the button action string denotes.*/private class CommandAction implements ActionListener{public void actionPerformed(ActionEvent event){String command = ActionCommand();if (start){if (command.equals("-")){display.setText(command);start = false;}else lastCommand = command;}else{calculate(Double.Text()));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