Minesweeper map generation in Java

MineSweeper.java

// Save this as MineSweeper.java
// compile with this command
// javac MineSweeper.java
// then run with this command
// java MineSweeper

// We need this for random numbers.
import java.util.Random;

class MineSweeper {
  int mWidth = 30; // width of the minefield
  int mHeight = 16; // height of the minefield
  int mMines = 99; // number of mines
  char[][] mMinefield; // 2-dimensional array of chars for our board

  public MineSweeper() {
    System.out.println("Generating minefield...");

    mMinefield = new char[mHeight][mWidth];

    System.out.println("Clearing minefield...");

    clearMinefield();

    System.out.println("Placing mines...");

    placeMines();
    drawMinefield();

    System.out.println("Calculating hints...");

    calculateHints();
    drawMinefield();
  }

  public void placeMines() {
    int minesPlaced = 0;
    Random random = new Random(); // this generates random numbers for us
    while(minesPlaced < mMines) {
      int x = random.nextInt(mWidth); // a number between 0 and mWidth - 1
      int y = random.nextInt(mHeight);
      // make sure we don't place a mine on top of another
      if(mMinefield[y][x] != '*') {
        mMinefield[y][x] = '*';
        minesPlaced ++;
      }
    }
  }

  public void clearMinefield() {
    // Set every grid space to a space character.
    for(int y = 0; y < mHeight; y ++) {
      for(int x = 0; x < mWidth; x ++) {
        mMinefield[y][x] = ' ';
      }
    }
  }

  public void drawMinefield() {
    for(int y = 0; y < mHeight; y ++) {
      for(int x = 0; x < mWidth; x ++) {
        System.out.print(mMinefield[y][x]);
      }
      System.out.print("\n");
    }
  }

  public void calculateHints() {
    for(int y = 0; y < mHeight; y ++) {
      for(int x = 0; x < mWidth; x ++) {
        if(mMinefield[y][x] != '*') {
          mMinefield[y][x] = minesNear(y, x);
        }
      }
    }
  }

  public char minesNear(int y, int x) {
    int mines = 0;
    // check mines in all directions
    mines += mineAt(y - 1, x - 1);  // NW
    mines += mineAt(y - 1, x);      // N
    mines += mineAt(y - 1, x + 1);  // NE
    mines += mineAt(y, x - 1);      // W
    mines += mineAt(y, x + 1);      // E
    mines += mineAt(y + 1, x - 1);  // SW
    mines += mineAt(y + 1, x);      // S
    mines += mineAt(y + 1, x + 1);  // SE
    if(mines > 0) {
      // we're changing an int to a char
      // why?!
      // http://www.asciitable.com/
      // 48 is ASCII code for '0'
      return (char)(mines + 48);
    } else {
      return ' ';
    }
  }

  // returns 1 if there's a mine a y,x or 0 if there isn't
  public int mineAt(int y, int x) {
    // we need to check also that we're not out of array bounds as that would
    // be an error
    if(y >= 0 && y < mHeight && x >= 0 && x < mWidth && mMinefield[y][x] == '*') {
      return 1;
    } else {
      return 0;
    }
  }

  // this starts the command line application
  public static void main(String[] args) {
    MineSweeper mineSweeper = new MineSweeper();
  }
}