用java实现扫雷游戏，且给出代码，并满足以下要求：1. 能自动生成地雷的布局，而不能像预备知识中源文件那样是固定的地雷布局。2. 能够让玩家在进入新游戏之前可以选择游戏的难度（Easy、Intermediate 和 Difficult），难度可以从“棋盘”的大小和地雷的数量两个维度进行设定，具体规则自定义。3. 创建一个“File”菜单，该菜单具有如下菜单项：New Game、Reset Game 和 Exit。提示：可以使用 JMenuBar、JMenu 和 JMenuItem 类类型。

下面是一个使用 Java 实现的扫雷游戏的代码例子，它满足您给出的要求。这个例子使用了 Swing 库来创建图形用户界面（GUI）：

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JOptionPane;

public class MineSweeper extends JFrame implements ActionListener {
  private static final long serialVersionUID = 1L;

  private static final String[] DIFFICULTIES = {"Easy", "Intermediate", "Difficult"};
  private static final int[][] DIFFICULTY_SETTINGS = {{8, 8, 10}, {16, 16, 40}, {16, 30, 99}};

  private MineField mineField;

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

  public MineSweeper() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setTitle("Mine Sweeper");

    JMenuBar menuBar = new JMenuBar();
    setJMenuBar(menuBar);

    JMenu fileMenu = new JMenu("File");
    menuBar.add(fileMenu);

    JMenuItem newGameMenuItem = new JMenuItem("New Game");
    newGameMenuItem.addActionListener(this);
    fileMenu.add(newGameMenuItem);

    JMenuItem resetGameMenuItem = new JMenuItem("Reset Game");
    resetGameMenuItem.addActionListener(this);
    fileMenu.add(resetGameMenuItem);

    JMenuItem exitMenuItem = new JMenuItem("Exit");
    exitMenuItem.addActionListener(this);
    fileMenu.add(exitMenuItem);

    startNewGame();
  }

  private void startNewGame() {
    int difficulty = JOptionPane.showOptionDialog(
        this, "Choose a difficulty:", "New Game",
        JOptionPane.DEFAULT_OPTION, JOptionPane.PLAIN_MESSAGE,
        null, DIFFICULTIES, DIFFICULTIES[0]);
    if (difficulty == JOptionPane.CLOSED_OPTION) {
      System.exit(0);
    }
    int rows = DIFFICULTY_SETTINGS[difficulty][0];
    int cols = DIFFICULTY_SETTINGS[difficulty][1];
    int mines = DIFFICULTY_SETTINGS[difficulty][2];
    mineField = new MineField(rows, cols, mines);
    setLayout(new GridLayout(rows, cols));
    for (int row = 0; row < rows; row++) {
      for