参考：http://yuncode.net/code/c_50b0c000f0c2e62
作者：程序猿style

界面.png

源码

package top.warmj.calculator;

import java.awt.*;
import java.awt.event.*;

public class Calc extends Frame implements ActionListener {
    Font font = new Font("宋体", Font.PLAIN, 24); // 全局字体，字体无效
    private Button b_7;
    private Button b_8;
    private Button b_9;
    private Button b_divi; // 除号
    private Button b_4;
    private Button b_5;
    private Button b_6;
    private Button b_multi; // 乘号
    private Button b_1;
    private Button b_2;
    private Button b_3;
    private Button b_sub; // 减号
    private Button b_dot; // 小数点
    private Button b_0;
    private Button b_equal; // 等于号
    private Button b_plus; // 加号
    private TextField tf_result; // 结果显示框
    private Button b_clear;
    private double resultNum = 0.0;
    private Button b_backspace;
    private Boolean isFirstNum = true; // 是否第一个数字，或按下运算按钮后的第一个数字
    private boolean isValid = true; // 操作是否合法
    private String operator = "="; // 当前运算的运算符
    private Button[] numButtonArrs; // 数字按钮数组
    private Button[] opeButtonArrs; // 运算符等按钮数组

    public static void main(String[] args) {
        new Calc("Simple Calculator —— WarMj");
    }

    // 程序功能
    public Calc() {
        init();
    }

    public Calc(String name) {
        super(name);
        init();
    }

    // 初始化
    public void init() {
        this.setSize(500, 270);
        this.setLocation(750, 400);
        this.setIconImage(Toolkit.getDefaultToolkit().createImage("calc.png"));
        this.setVisible(true);
        this.setResizable(false);
        northPanel();
        centerPanel();
        event();
    }

    // 按键点击动作监听
    public void actionPerformed(ActionEvent e) {
        // 获取事件源的标签
        String label = e.getActionCommand();
        if (label.equals(opeButtonArrs[5].getLabel())) {
            // 点击"Backspace"键
            handleBackspace();
        } else if (label.equals(opeButtonArrs[6].getLabel())) {
            // 点击"CE"键
            tf_result.setText("");
        } else if ("0123456789.".indexOf(label) >= 0) {
            // 点击数字键或者小数点键
            handleNumber(label);
        } else {
            // 用户点击运算符键
            handleOperator(label);
        }
    }

    // 运算符键功能
    private void handleOperator(String key) {
        if (operator.equals("/")) {
            // 除法运算
            // 如果当前结果文本框中的值等于0
            if (getNumberFromText() == 0.0) {
                // 操作不合法
                isValid = false;
                tf_result.setText("除数不能为零");
            } else {
                resultNum /= getNumberFromText();
            }
        } else if (operator.equals("+")) {
            // 加法运算
            resultNum += getNumberFromText();
        } else if (operator.equals("-")) {
            // 减法运算
            resultNum -= getNumberFromText();
        } else if (operator.equals("*")) {
            // 乘法运算
            resultNum *= getNumberFromText();
        } else if (operator.equals("=")) {
            // 赋值运算
            resultNum = getNumberFromText();
        }
        if (isValid) {
            // 双精度浮点数的运算
            long t1; // 存放长整数
            double t2; // 判断差值
            t1 = (long) resultNum;
            t2 = resultNum - t1;

            if (t2 == 0) {
                // 没有差值，说明是值是整数，这样没有小数点
                tf_result.setText(String.valueOf(t1));
            } else {
                // 有差值，说明是浮点数
                tf_result.setText(String.valueOf(resultNum));
            }
        }

        // 运算符等于用户按的按钮
        operator = key;
        isFirstNum = true;
        isValid = true;
    }

    // 数字键或小数点键功能
    private void handleNumber(String key) {
        if (isFirstNum) {
            // 如果输入的是第一个数字
            tf_result.setText(key);
        } else if (key.equals(".") && (tf_result.getText().indexOf(".") < 0)) {
            tf_result.setText(tf_result.getText() + ".");
        } else if (!key.equals(".")) {
            tf_result.setText(tf_result.getText() + key);
        }

        // 以后输入的就不是第一个数字了
        isFirstNum = false;
    }

    // 退格键功能
    private void handleBackspace() {
        if (tf_result.getText().equals("")) {
            isFirstNum = true;
            resultNum = 0.0;
            operator = "=";
        } else {
            String str = tf_result.getText();
            tf_result.setText(str.substring(0, str.length() - 1));
        }
    }

    // 事件
    public void event() {
        // 创建键盘监听对象
        KeyAdapter keyadapter = new KeyAdapter() {
            public void keyPressed(KeyEvent e) {
                if (e.getKeyCode() > 47 && e.getKeyCode() < 58) {
                    handleNumber(e.getKeyText(e.getKeyCode()));
                } else if (e.getKeyCode() > 95 && e.getKeyCode() < 106) {
                    handleNumber(e.getKeyText(e.getKeyCode()).substring(7, 8));
                }

                switch (e.getKeyCode()) {
                    case 106: // 乘号 *
                        handleOperator("*");
                        break;
                    case 61:
                    case 107: // 加号 +
                        handleOperator("+");
                        break;
                    case 45:
                    case 109: // 减号 -
                        handleOperator("-");
                        break;
                    case 111: // 除号 /
                        handleOperator("/");
                        break;
                    case 10: // 回车 Enter
                        handleOperator("=");
                        break;
                    case 8: // 退格 Backpace
                        handleBackspace();
                        break;
                    case 46:
                    case 110: // 小数点 .
                        handleNumber(".");
                        break;
                    case 27:
                        tf_result.setText("");
                        break;
                    default:
                        break;
                }
            }
        };

        // 添加键盘监听事件
        tf_result.addKeyListener(keyadapter);

        for (int i = 0; i < numButtonArrs.length; i++) {
            // 给按钮添加监听事件，由于本类已经实现 ActionListener 接口，所以直接用 this
            numButtonArrs[i].addActionListener(this); // 点击
            numButtonArrs[i].addKeyListener(keyadapter); // 按钮
        }

        for (int i = 0; i < opeButtonArrs.length; i++) {
            opeButtonArrs[i].addActionListener(this); // 点击
            opeButtonArrs[i].addKeyListener(keyadapter); // 按钮
        }

        // 关闭窗口
        this.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
    }

    // 北布局，计算结果和清零按钮
    public void northPanel() {
        Panel north = new Panel();

        // 结果框
        tf_result = new TextField();
        tf_result.setEditable(false);
        tf_result.setBackground(Color.WHITE);
        tf_result.setColumns(25);
        tf_result.setFont(font);
        tf_result.setText("");

        // 退格按钮
        b_backspace = new Button("←");
        b_backspace.setPreferredSize(new Dimension(50, 35));
        b_backspace.setFont(font);

        // 清零按钮
        b_clear = new Button("CE");
        b_clear.setPreferredSize(new Dimension(50, 35));
        b_clear.setFont(font);

        north.add(tf_result);
        north.add(b_backspace);
        north.add(b_clear);
        this.add(north, BorderLayout.NORTH);
    }

    // 中间布局，其他运算按钮
    public void centerPanel() {
        Panel center = new Panel();

        b_7 = getButton("7");
        b_8 = getButton("8");
        b_9 = getButton("9");
        b_divi = getButton("/");
        b_4 = getButton("4");
        b_5 = getButton("5");
        b_6 = getButton("6");
        b_multi = getButton("*");
        b_1 = getButton("1");
        b_2 = getButton("2");
        b_3 = getButton("3");
        b_sub = getButton("-");
        b_dot = getButton(".");
        b_0 = getButton("0");
        b_equal = getButton("=");
        b_plus = getButton("+");

        // 数字和小数点按钮数组
        numButtonArrs = new Button[] { b_0, b_1, b_2, b_3, b_4, b_5, b_6, b_7, b_8, b_9, b_dot };

        // 运算符按钮数组
        opeButtonArrs = new Button[] { b_plus, b_sub, b_multi, b_divi, b_equal, b_backspace, b_clear };

        center.add(b_7);
        center.add(b_8);
        center.add(b_9);
        center.add(b_divi);
        center.add(b_4);
        center.add(b_5);
        center.add(b_6);
        center.add(b_multi);
        center.add(b_1);
        center.add(b_2);
        center.add(b_3);
        center.add(b_sub);
        center.add(b_dot);
        center.add(b_0);
        center.add(b_equal);
        center.add(b_plus);

        center.setVisible(true);
        this.add(center, BorderLayout.CENTER);
    }

    // 获取按钮功能
    public Button getButton(String name) {
        Button button = new Button(name);
        button.setPreferredSize(new Dimension(115, 40));
        button.setFont(font);

        return button;
    }

    // 获取当前数字
    private double getNumberFromText() {
        double result = 0.0;
        try {
            result = Double.valueOf(tf_result.getText()).doubleValue();
        } catch (NumberFormatException e) {
        }
        return result;
    }
}

calc.png