3．编写程序实现一个简单计算器的基本功能，具体可以模仿Windows附件中的计算器或模拟常见的实物计算器。使用java

以下是一个简单的基于Java Swing的计算器程序实现：

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

public class Calculator extends JFrame implements ActionListener {

    private static final long serialVersionUID = 1L;
    private JPanel panel;
    private JButton[] buttons;
    private JTextField display;
    private String[] buttonLabels = {"7", "8", "9", "/", "4", "5", "6", "*", "1", "2", "3", "-", "0", ".", "=", "+"};
    private double result = 0;
    private String operator = "";
    private boolean start = true;

    public Calculator() {
        super("Calculator");
        setSize(300, 300);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
        setResizable(false);

        panel = new JPanel();
        panel.setLayout(new GridLayout(4, 4));

        buttons = new JButton[buttonLabels.length];
        for (int i = 0; i < buttonLabels.length; i++) {
            buttons[i] = new JButton(buttonLabels[i]);
            buttons[i].addActionListener(this);
            panel.add(buttons[i]);
        }

        display = new JTextField();
        display.setEditable(false);
        display.setHorizontalAlignment(JTextField.RIGHT);

        getContentPane().add(display, BorderLayout.NORTH);
        getContentPane().add(panel, BorderLayout.CENTER);

        setVisible(true);
    }

    public void actionPerformed(ActionEvent event) {
        String command = event.getActionCommand();
        if (command.matches("[0-9\\.]")) {
            if (start) {
                display.setText(command);
                start = false;
            } else {
                display.setText(display.getText() + command);
            }
        } else if (command.matches("[+\\-*/=]")) {
            if (operator.equals("")) {
                result = Double.parseDouble(display.getText());
            } else if (operator.equals("+")) {
                result += Double.parseDouble(display.getText());
            } else if (operator.equals("-")) {
                result -= Double.parseDouble(display.getText());
            } else if (operator.equals("*")) {
                result *= Double.parseDouble(display.getText());
            } else if (operator.equals("/")) {
                result /= Double.parseDouble(display.getText());
            }
            display.setText("" + result);
            operator = command;
            start = true;
        }
    }

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

}

该程序使用GridLayout布局管理器来排列按钮，并实现了ActionListener接口以处理按钮点击事件。在actionPerformed方法中，程序先判断点击的按钮是数字还是运算符，然后根据不同的运算符来计算结果，并将结果显示在文本框中。