用java怎么写

如果你想在Java中实现一个计算器，可以通过创建一个图形用户界面（GUI）来实现用户输入和输出的交互效果。下面是一个简单的Java GUI计算器示例：

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

public class Calculator extends JFrame implements ActionListener {
    private JTextField displayField;
    private JButton button0, button1, button2, button3, button4, 
                    button5, button6, button7, button8, button9,
                    buttonAdd, buttonSub, buttonMul, buttonDiv, buttonEq,
                    buttonClear, buttonDot;
    double num1, num2, result;
    int operator;

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

        //创建显示面板
        JPanel displayPanel = new JPanel();
        displayField = new JTextField(20);
        displayField.setEditable(false);
        displayField.setHorizontalAlignment(JTextField.RIGHT);
        displayPanel.add(displayField);

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

        //创建数字按钮
        button7 = new JButton("7");
        button7.addActionListener(this);
        buttonPanel.add(button7);

        button8 = new JButton("8");
        button8.addActionListener(this);
        buttonPanel.add(button8);

        button9 = new JButton("9");
        button9.addActionListener(this);
        buttonPanel.add(button9);

        buttonDiv = new JButton("/");
        buttonDiv.addActionListener(this);
        buttonPanel.add(buttonDiv);

        button4 = new JButton("4");
        button4.addActionListener(this);
        buttonPanel.add(button4);

        button5 = new JButton("5");
        button5.addActionListener(this);
        buttonPanel.add(button5);

        button6 = new JButton("6");
        button6.addActionListener(this);
        buttonPanel.add(button6);

        buttonMul = new JButton("*");
        buttonMul.addActionListener(this);
        buttonPanel.add(buttonMul);

        button1 = new JButton("1");
        button1.addActionListener(this);
        buttonPanel.add(button1);

        button2 = new JButton("2");
        button2.addActionListener(this);
        buttonPanel.add(button2);

        button3 = new JButton("3");
        button3.addActionListener(this);
        buttonPanel.add(button3);

        buttonSub = new JButton("-");
        buttonSub.addActionListener(this);
        buttonPanel.add(buttonSub);

        button0 = new JButton("0");
        button0.addActionListener(this);
        buttonPanel.add(button0);

        buttonDot = new JButton(".");
        buttonDot.addActionListener(this);
        buttonPanel.add(buttonDot);

        buttonEq = new JButton("=");
        buttonEq.addActionListener(this);
        buttonPanel.add(buttonEq);

        buttonAdd = new JButton("+");
        buttonAdd.addActionListener(this);
        buttonPanel.add(buttonAdd);

        buttonClear = new JButton("C");
        buttonClear.addActionListener(this);
        buttonPanel.add(buttonClear);

        //将面板添加到窗体中
        add(displayPanel, BorderLayout.NORTH);
        add(buttonPanel, BorderLayout.CENTER);

        //设置窗体属性
        setSize(300, 300);
        setLocationRelativeTo(null);
        setResizable(false);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
    }

    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == button0) {
            displayField.setText(displayField.getText() + "0");
        } else if (e.getSource() == button1) {
            displayField.setText(displayField.getText() + "1");
        } else if (e.getSource() == button2) {
            displayField.setText(displayField.getText() + "2");
        } else if (e.getSource() == button3) {
            displayField.setText(displayField.getText() + "3");
        } else if (e.getSource() == button4) {
            displayField.setText(displayField.getText() + "4");
        } else if (e.getSource() == button5) {
            displayField.setText(displayField.getText() + "5");
        } else if (e.getSource() == button6) {
            displayField.setText(displayField.getText() + "6");
        } else if (e.getSource() == button7) {
            displayField.setText(displayField.getText() + "7");
        } else if (e.getSource() == button8) {
            displayField.setText(displayField.getText() + "8");
        } else if (e.getSource() == button9) {
            displayField.setText(displayField.getText() + "9");
        } else if (e.getSource() == buttonDot) {
            displayField.setText(displayField.getText() + ".");
        } else if (e.getSource() == buttonAdd) {
            num1 = Double.parseDouble(displayField.getText());
            operator = 1;
            displayField.setText("");
        } else if (e.getSource() == buttonSub) {
            num1 = Double.parseDouble(displayField.getText());
            operator = 2;
            displayField.setText("");
        } else if (e.getSource() == buttonMul) {
            num1 = Double.parseDouble(displayField.getText());
            operator = 3;
            displayField.setText("");
        } else if (e.getSource() == buttonDiv) {
            num1 = Double.parseDouble(displayField.getText());
            operator = 4;
            displayField.setText("");
        } else if (e.getSource() == buttonClear) {
            displayField.setText("");
        } else if (e.getSource() == buttonEq) {
            num2 = Double.parseDouble(displayField.getText());
            switch (operator) {
                case 1:
                    result = num1 + num2;
                    break;
                case 2:
                    result = num1 - num2;
                    break;
                case 3:
                    result = num1 * num2;
                    break;
                case 4:
                    result = num1 / num2;
                    break;
                default:
                    break;
            }
            displayField.setText(String.valueOf(result));
        }
    }

    public static void main(String[] args) {
        new Calculator();
    }
}

这个示例中创建了一个JFrame窗体，并添加了一个JTextField文本框用于显示计算结果，以及一组JButton按钮用于输入数字和操作符。当用户点击数字按钮时，程序会将数字添加到文本框中；当用户点击操作符按钮时，程序会记录当前的数字以及操作符；当用户点击等号按钮时，程序会根据当前的数字和操作符计算结果并显示在文本框中。