java设计和编写一个简易的计算器：实现计算器的界面；实现计算按钮不同的计算功能；显示计算器按钮运算后的结果。要求：按钮C在输入框旁边，剩下的按钮顺序为 1 2 3 + 4 5 6 - 7 8 9 * 0 . = /

以下是一个简单的Java计算器的代码示例：

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Calculator extends JFrame implements ActionListener {

    private JTextField display;
    private double num1, num2, result;
    private String operator;

    public Calculator() {
        super("Calculator");
        setLayout(new BorderLayout());

        // 创建显示框
        display = new JTextField("0");
        display.setEditable(false);
        add(display, BorderLayout.NORTH);

        // 创建按钮面板
        JPanel buttonPanel = new JPanel();
        buttonPanel.setLayout(new GridLayout(4, 4));

        // 添加按钮
        addButton(buttonPanel, "C");
        addButton(buttonPanel, "1");
        addButton(buttonPanel, "2");
        addButton(buttonPanel, "3");
        addButton(buttonPanel, "+");
        addButton(buttonPanel, "4");
        addButton(buttonPanel, "5");
        addButton(buttonPanel, "6");
        addButton(buttonPanel, "-");
        addButton(buttonPanel, "7");
        addButton(buttonPanel, "8");
        addButton(buttonPanel, "9");
        addButton(buttonPanel, "*");
        addButton(buttonPanel, "0");
        addButton(buttonPanel, ".");
        addButton(buttonPanel, "=");
        addButton(buttonPanel, "/");

        add(buttonPanel, BorderLayout.CENTER);

        // 添加计算器事件监听器
        num1 = 0;
        num2 = 0;
        result = 0;
        operator = "";
    }

    // 添加按钮方法
    private void addButton(Container c, String label) {
        JButton button = new JButton(label);
        button.addActionListener(this);
        c.add(button);
    }

    // 处理按钮事件
    public void actionPerformed(ActionEvent event) {
        String command = event.getActionCommand();

        if (command.equals("C")) {
            // 清除显示框
            display.setText("0");
            num1 = 0;
            num2 = 0;
            result = 0;
            operator = "";
        } else if (command.equals("+") || command.equals("-") || command.equals("*") || command.equals("/")) {
            // 处理运算符
            num1 = Double.parseDouble(display.getText());
            operator = command;
            display.setText("");
        } else if (command.equals("=")) {
            // 处理等号
            num2 = Double.parseDouble(display.getText());
            if (operator.equals("+")) {
                result = num1 + num2;
            } else if (operator.equals("-")) {
                result = num1 - num2;
            } else if (operator.equals("*")) {
                result = num1 * num2;
            } else if (operator.equals("/")) {
                result = num1 / num2;
            }
            display.setText(String.valueOf(result));
        } else {
            // 处理数字和小数点
            String currentText = display.getText();
            if (currentText.equals("0")) {
                currentText = "";
            }
            display.setText(currentText + command);
        }
    }

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

该计算器使用 `JTextField` 显示计算结果和输入数字、运算符，使用 `JButton` 添加数字和运算符按钮，使用 `GridLayout` 将按钮添加到面板中。在 `actionPerformed` 方法中，根据不同的按钮处理不同的事件，包括清除显示框、处理运算符、处理等号以及输入数字和小数点等。最后，通过 `JFrame` 显示计算器界面。