Java编写计算器

主要用JAVA编写一个计算器，能实现加减乘除、开平方、求阶乘等计算功能,计算器有图形化界面，能对异常进行处理，并且检验输入的合法性，对不合法的输入给出具体的提示信息
代码如下

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class CalculatorFrame extends JFrame implements ActionListener {
	private JTextField resultDisplay; //结果显示文本框
    private double num1; //第一个数字
    private double num2; //第二个数字
    private char operator = 'C'; //操作符，默认为清屏

    public CalculatorFrame() 
    {
        super("计算器");

        JPanel mainPanel = new JPanel(); //主面板
        mainPanel.setLayout(new BorderLayout());

        resultDisplay = new JTextField(); //结果显示文本框
        resultDisplay.setEditable(false); //不能编辑
        mainPanel.add(resultDisplay, BorderLayout.NORTH); //添加到面板上方

        JPanel buttonPanel = new JPanel(new GridLayout(5, 4, 5, 5)); //按钮面板，4行4列，行列间距为5

        addButton(buttonPanel, "7"); 
        addButton(buttonPanel, "8");
        addButton(buttonPanel, "9");
        addButton(buttonPanel, "÷"); //添加按钮：“7”、“8”、“9”、“÷”

        addButton(buttonPanel, "4");
        addButton(buttonPanel, "5");
        addButton(buttonPanel, "6");
        addButton(buttonPanel, "×"); //添加按钮：“4”、“5”、“6”、“×”

        addButton(buttonPanel, "1");
        addButton(buttonPanel, "2");
        addButton(buttonPanel, "3");
        addButton(buttonPanel, "-"); //添加按钮：“1”、“2”、“3”、“-”

        addButton(buttonPanel, "0");
        addButton(buttonPanel, ".");
        addButton(buttonPanel, "C");
        addButton(buttonPanel, "+"); //添加按钮：“0”、“.”、“C”、“+”

        addButton(buttonPanel, "x²");
        addButton(buttonPanel, "√");
        addButton(buttonPanel, "x!");
        addButton(buttonPanel, "="); //添加按钮：“x²”、“√”、“x!”、“=” 

        mainPanel.add(buttonPanel, BorderLayout.CENTER); //添加按钮面板，位于主面板的中央

        JButton equalsButton = new JButton("="); //等于号按钮
        equalsButton.addActionListener(this); //添加事件响应器
        mainPanel.add(equalsButton, BorderLayout.SOUTH); //添加到主面板下方

        add(mainPanel); //将主面板添加到窗口中
    }

    private void addButton(Container panel, String label) 
    {
        JButton button = new JButton(label); //新建按钮
        button.addActionListener(this); //添加事件响应器
        panel.add(button); //添加到按钮面板中
    }

    // 响应用户操作事件
    public void actionPerformed(ActionEvent evt) 
    {
        String text = evt.getActionCommand(); //获取用户操作

        if (text.equals("C")) 
        { //清屏
            resultDisplay.setText("");
            num1 = 0;
            num2 = 0;
            operator = 'C';
            return;
        }

        if (text.equals("x²")) 
        { //平方
            num1 = Double.parseDouble(resultDisplay.getText()); //获取当前数字
            resultDisplay.setText(String.valueOf(num1 * num1)); //计算平方并显示
            operator = 'C';
            return;
        }

        if (text.equals("√")) 
        { //开方
            num1 = Double.parseDouble(resultDisplay.getText()); //获取当前数字
            if (num1 < 0) 
            { //负数不能开方
                resultDisplay.setText("不能对负数求平方根");
                return;
            }
            resultDisplay.setText(String.valueOf(Math.sqrt(num1))); //计算开方并显示
            operator = 'C';
            return;
        }

        if (text.equals("x!")) 
        { //阶乘
            num1 = Double.parseDouble(resultDisplay.getText()); //获取当前数字
            resultDisplay.setText(String.valueOf(factorial(num1))); //计算阶乘并显示
            operator = 'C';
            return;
        }

        if (text.equals("+") || text.equals("-") || text.equals("×") ||
            text.equals("÷")) 
        { //基本运算
            num1 = Double.parseDouble(resultDisplay.getText()); //获取第一个数字
            operator = text.charAt(0); //获取操作符
            resultDisplay.setText(""); //清空结果文本框
            return;
        }

        if (text.equals("=")) 
        { //计算结果
            num2 = Double.parseDouble(resultDisplay.getText()); //获取第二个数字

            switch (operator) { //选择合适的操作符进行计算
            case '+':
                resultDisplay.setText(String.valueOf(num1 + num2));
                break;
            case '-':
                resultDisplay.setText(String.valueOf(num1 - num2));
                break;
            case '×':
                resultDisplay.setText(String.valueOf(num1 * num2));
                break;
            case '÷':
                if (num2 == 0) 
                { //除数不能为零
                    resultDisplay.setText("除数不能为零");
                    return;
                }
                resultDisplay.setText(String.valueOf(num1 / num2));
                break;
        }

        operator = 'C'; //清除操作符
        return;
        }

    resultDisplay.setText(resultDisplay.getText() + text); //输出数字或小数点
    }

    // 计算阶乘
    public static double factorial(double num) 
    {
    	if (num == 0)
    		return 1;

    	double result = 1;

    	for (int i = 1; i <= num; i++) 
    	{
    		result *= i;
    	}

    	return result;
    }

    public static void main(String[] args) 
    {
    	CalculatorFrame calculator = new CalculatorFrame();
    	calculator.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    	calculator.setSize(300, 350);
    	calculator.setVisible(true);
    }
}