编写一个模拟计算器的程序，使用面板和网格布局，添加一个文本框，10个数字按钮(0-9)，3个加减除按钮，一个等号按钮，一个清除按钮，要求将计算公式和结果显示在文本框中。

以下是一个使用Java Swing库编写的模拟计算器程序的示例代码，包括面板和网格布局，文本框，数字和操作符按钮以及事件处理程序。

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

public class Calculator extends JFrame implements ActionListener {
    private JTextField textField;
    private JButton[] numberButtons = new JButton[10];
    private JButton[] operationButtons = new JButton[4];
    private JButton clearButton, equalsButton;
    private JPanel panel;

    private double num1 = 0, num2 = 0, result = 0;
    private char operator;

    public Calculator() {
        setTitle("Calculator");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(300, 400);

        textField = new JTextField();
        textField.setPreferredSize(new Dimension(250, 50));
        textField.setEditable(false);

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

        for(int i = 0; i < 10; i++) {
            numberButtons[i] = new JButton(String.valueOf(i));
            numberButtons[i].addActionListener(this);
        }

        operationButtons[0] = new JButton("+");
        operationButtons[1] = new JButton("-");
        operationButtons[2] = new JButton("*");
        operationButtons[3] = new JButton("/");
        for(int i = 0; i < 4; i++) {
            operationButtons[i].addActionListener(this);
        }

        clearButton = new JButton("C");
        clearButton.addActionListener(this);

        equalsButton = new JButton("=");
        equalsButton.addActionListener(this);

        panel.add(numberButtons[1]);
        panel.add(numberButtons[2]);
        panel.add(numberButtons[3]);
        panel.add(operationButtons[0]);
        panel.add(numberButtons[4]);
        panel.add(numberButtons[5]);
        panel.add(numberButtons[6]);
        panel.add(operationButtons[1]);
        panel.add(numberButtons[7]);
        panel.add(numberButtons[8]);
        panel.add(numberButtons[9]);
        panel.add(operationButtons[2]);
        panel.add(clearButton);
        panel.add(numberButtons[0]);
        panel.add(equalsButton);
        panel.add(operationButtons[3]);

        add(textField, BorderLayout.NORTH);
        add(panel, BorderLayout.CENTER);

        setVisible(true);
    }

    public void actionPerformed(ActionEvent e) {
        for(int i = 0; i < 10; i++) {
            if(e.getSource() == numberButtons[i]) {
                textField.setText(textField.getText().concat(String.valueOf(i)));
            }
        }
        if(e.getSource() == operationButtons[0]) {
            num1 = Double.parseDouble(textField.getText());
            operator = '+';
            textField.setText("");
        }
        if(e.getSource() == operationButtons[1]) {
            num1 = Double.parseDouble(textField.getText());
            operator = '-';
            textField.setText("");
        }
        if(e.getSource() == operationButtons[2]) {
            num1 = Double.parseDouble(textField.getText());
            operator = '*';
            textField.setText("");
        }
        if(e.getSource() == operationButtons[3]) {
            num1 = Double.parseDouble(textField.getText());
            operator = '/';
            textField.setText("");
        }
        if(e.getSource() == equalsButton) {
            num2 = Double.parseDouble(textField.getText());
            switch(operator) {
                case '+':
                    result = num1 + num2;
                    break;
                case '-':
                    result = num1 - num2;
                    break;
                case '*':
                    result = num1 * num2;
                    break;
                case '/':
                    result = num1 / num2;
                    break;
            }
            textField.setText(String.valueOf(result));
            num1 = result;
        }
        if(e.getSource() == clearButton) {
            textField.setText("");
        }
    }

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