设计并实现一个类似于windows操作系统附件中自带的计算器的一款简单的计算器，要求界面美观，设计合理；带有常用的菜单并实现其功能；能完成加、减、乘、除等简单的计算，在下面用java写出其核心代码。

很高兴收到您的问题，以下是代码实现：

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

public class Calculator extends JFrame {

    private JPanel jPanel;
    private JTextField jTextField;
    private JButton button1, button2, button3, button4, button5, button6, button7, button8, button9, button0, buttonAdd, buttonMinus, buttonMultiply, buttonDivide, buttonEqual, buttonDot, buttonClear;
    private double firstNum;
    private String operator;

    public Calculator() {
        initUI();
    }

    private void initUI() {
        setLayout(new BorderLayout());

        jPanel = new JPanel();
        jPanel.setLayout(new GridLayout(5, 4, 5, 5));

        jTextField = new JTextField("");
        jTextField.setHorizontalAlignment(JTextField.RIGHT);
        jTextField.setEditable(false);

        buttonClear = new JButton("C");
        button1 = new JButton("1");
        button2 = new JButton("2");
        button3 = new JButton("3");
        buttonAdd = new JButton("+");

        button4 = new JButton("4");
        button5 = new JButton("5");
        button6 = new JButton("6");
        buttonMinus = new JButton("-");

        button7 = new JButton("7");
        button8 = new JButton("8");
        button9 = new JButton("9");
        buttonMultiply = new JButton("*");

        buttonDot = new JButton(".");
        button0 = new JButton("0");
        buttonEqual = new JButton("=");
        buttonDivide = new JButton("/");

        buttonClear.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                jTextField.setText("");
            }
        });

        button1.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                jTextField.setText(jTextField.getText() + "1");
            }
        });

        button2.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                jTextField.setText(jTextField.getText() + "2");
            }
        });

        button3.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                jTextField.setText(jTextField.getText() + "3");
            }
        });

        button4.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                jTextField.setText(jTextField.getText() + "4");
            }
        });

        button5.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                jTextField.setText(jTextField.getText() + "5");
            }
        });

        button6.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                jTextField.setText(jTextField.getText() + "6");
            }
        });

        button7.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                jTextField.setText(jTextField.getText() + "7");
            }
        });

        button8.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                jTextField.setText(jTextField.getText() + "8");
            }
        });

        button9.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                jTextField.setText(jTextField.getText() + "9");
            }
        });

        button0.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                jTextField.setText(jTextField.getText() + "0");
            }
        });

        buttonAdd.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                firstNum = Double.parseDouble(jTextField.getText());
                operator = "+";
                jTextField.setText("");
            }
        });

        buttonMinus.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                firstNum = Double.parseDouble(jTextField.getText());
                operator = "-";
                jTextField.setText("");
            }
        });

        buttonMultiply.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                firstNum = Double.parseDouble(jTextField.getText());
                operator = "*";
                jTextField.setText("");
            }
        });

        buttonDivide.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                firstNum = Double.parseDouble(jTextField.getText());
                operator = "/";
                jTextField.setText("");
            }
        });

        buttonDot.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                jTextField.setText(jTextField.getText() + ".");
            }
        });

        buttonEqual.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                double secondNum = Double.parseDouble(jTextField.getText());
                if (operator.equals("+")) {
                    jTextField.setText(String.valueOf(firstNum + secondNum));
                } else if (operator.equals("-")) {
                    jTextField.setText(String.valueOf(firstNum - secondNum));
                } else if (operator.equals("*")) {
                    jTextField.setText(String.valueOf(firstNum * secondNum));
                } else if (operator.equals("/")) {
                    jTextField.setText(String.valueOf(firstNum / secondNum));
                }
                operator = "";
            }
        });

        jPanel.add(buttonClear);
        jPanel.add(buttonDivide);
        jPanel.add(buttonMultiply);
        jPanel.add(buttonMinus);
        jPanel.add(button7);
        jPanel.add(button8);
        jPanel.add(button9);
        jPanel.add(buttonAdd);
        jPanel.add(button4);
        jPanel.add(button5);
        jPanel.add(button6);
        jPanel.add(buttonDot);
        jPanel.add(button1);
        jPanel.add(button2);
        jPanel.add(button3);
        jPanel.add(buttonEqual);
        jPanel.add(button0);

        add(jTextField, BorderLayout.NORTH);
        add(jPanel, BorderLayout.CENTER);

        setTitle("计算器");
        setLocationRelativeTo(null);
        setResizable(false);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(300, 400);
    }

    public static void main(String[] args) {
        Calculator calculator = new Calculator();
        calculator.setVisible(true);
    }
}

这是一个简单的计算器，可以进行加、减、乘、除和小数点运算，并且还具有清空和求和功能。希望能帮到你。