利用JAVA完成计算器的加、减、乘、除、开方、求反等功能，具体功能需求可以参考window自带计算器。完成对计算器界面开发的代码,完成计算器逻辑功能的开发

以下是一个简单的利用JAVA实现计算器的例子，包括基本的加、减、乘、除、开方和求反功能：

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

public class Calculator extends JFrame implements ActionListener {
    private static final long serialVersionUID = 1L;
    private JTextField textField;
    private JButton btn0, btn1, btn2, btn3, btn4, btn5, btn6, btn7, btn8, btn9;
    private JButton btnAdd, btnSub, btnMul, btnDiv, btnDot, btnEql, btnSqrt, btnNeg;

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

    public Calculator() {
        setTitle("Calculator");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(240, 300);
        setLocationRelativeTo(null);

        textField = new JTextField(15);
        textField.setHorizontalAlignment(JTextField.RIGHT);
        textField.setEditable(false);

        btn0 = new JButton("0");
        btn1 = new JButton("1");
        btn2 = new JButton("2");
        btn3 = new JButton("3");
        btn4 = new JButton("4");
        btn5 = new JButton("5");
        btn6 = new JButton("6");
        btn7 = new JButton("7");
        btn8 = new JButton("8");
        btn9 = new JButton("9");
        btnAdd = new JButton("+");
        btnSub = new JButton("-");
        btnMul = new JButton("*");
        btnDiv = new JButton("/");
        btnDot = new JButton(".");
        btnEql = new JButton("=");
        btnSqrt = new JButton("sqrt");
        btnNeg = new JButton("+/-");

        JPanel panel1 = new JPanel();
        panel1.setLayout(new GridLayout(4, 3));
        panel1.add(btn1);
        panel1.add(btn2);
        panel1.add(btn3);
        panel1.add(btn4);
        panel1.add(btn5);
        panel1.add(btn6);
        panel1.add(btn7);
        panel1.add(btn8);
        panel1.add(btn9);
        panel1.add(btn0);
        panel1.add(btnDot);
        panel1.add(btnNeg);

        JPanel panel2 = new JPanel();
        panel2.setLayout(new GridLayout(4, 1));
        panel2.add(btnAdd);
        panel2.add(btnSub);
        panel2.add(btnMul);
        panel2.add(btnDiv);

        JPanel panel3 = new JPanel();
        panel3.setLayout(new GridLayout(1, 2));
        panel3.add(btnSqrt);
        panel3.add(btnEql);

        JPanel contentPane = new JPanel();
        contentPane.setLayout(new BorderLayout());
        contentPane.add(textField, BorderLayout.NORTH);
        contentPane.add(panel1, BorderLayout.CENTER);
        contentPane.add(panel2, BorderLayout.EAST);
        contentPane.add(panel3, BorderLayout.SOUTH);

        setContentPane(contentPane);
        setVisible(true);

        btn0.addActionListener(this);
        btn1.addActionListener(this);
        btn2.addActionListener(this);
        btn3.addActionListener(this);
        btn4.addActionListener(this);
        btn5.addActionListener(this);
        btn6.addActionListener(this);
        btn7.addActionListener(this);
        btn8.addActionListener(this);
        btn9.addActionListener(this);
        btnAdd.addActionListener(this);
        btnSub.addActionListener(this);
        btnMul.addActionListener(this);
        btnDiv.addActionListener(this);
        btnDot.addActionListener(this);
        btnEql.addActionListener(this);
        btnSqrt.addActionListener(this);
        btnNeg.addActionListener(this);
    }

    public void actionPerformed(ActionEvent e) {
        String input = e.getActionCommand();
        if (input.equals("C")) {
            textField.setText("");
        } else if (input.equals("+/-")) {
            num1 = Double.parseDouble(textField.getText());
            num1 = -num1;
            textField.setText(Double.toString(num1));
        } else if (input.equals("sqrt")) {
            num1 = Double.parseDouble(textField.getText());
            num1 = Math.sqrt(num1);
            textField.setText(Double.toString(num1));
        } else if (input.equals("+")) {
            num1 = Double.parseDouble(textField.getText());
            operator = "+";
            textField.setText("");
        } else if (input.equals("-")) {
            num1 = Double.parseDouble(textField.getText());
            operator = "-";
            textField.setText("");
        } else if (input.equals("*")) {
            num1 = Double.parseDouble(textField.getText());
            operator = "*";
            textField.setText("");
        } else if (input.equals("/")) {
            num1 = Double.parseDouble(textField.getText());
            operator = "/";
            textField.setText("");
        } else if (input.equals("=")) {
            num2 = Double.parseDouble(textField.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;
            }
            textField.setText(Double.toString(result));
        } else {
            String currentText = textField.getText();
            currentText += input;
            textField.setText(currentText);
        }
    }

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

该程序使用了Java Swing库来创建GUI，实现了基本的加、减、乘、除、开方和求反功能。用户可以通过按钮输入数字和操作符，并且计算器会在文本框中显示结果。