在用户和计算机之间移动时战舰运行时错误

Question

我在战舰项目上遇到了一个问题。问题在于Move的检查和制作。

当我点击敌人板和计算机的轮到我得到空指针异常在hit = inShips[i]。checkMove (x, y);

这是完整的项目:http://db.tt/V6YiTJVw(你需要改变图像路径在selectionPanel和selectionFrame类)

谢谢你的帮助

 public void checkMove(JButton[][] inBoard, Ship[] inShips, int x, int y) {
        boolean hit = false;
       // Ship[] inShips = new Ship[5];
        int i = -1;
        System.out.println("CHECKING MOVE AT CLASS PLAYBOARD (checkMove): ");
        System.out.println("xCoord " + x);
        System.out.println("yCoord " + y);
        System.out.println("");
    //    do {
            i++;
            System.out.println("INSHIPS: ");
            System.out.println("!!!!!!!!!!!!!!!! " + i);
            hit = inShips[i].checkMove(x, y);
            System.out.println("IS HIT? : " + String.valueOf(hit));
     //   } while ((i < 4) && (!hit));

checkMove at ship class:

   public boolean checkMove(int x, int y)
  { 
    for (int i = 0; i < this.size; i++)
    {
      if ((this.shipCoords[i][0] == x) && (this.shipCoords[i][1] == y))
      {
        this.piecesHit += 1;
        this.lastPieceHit[0] = x;
        this.lastPieceHit[1] = y;
        if (this.piecesHit == this.size)
          this.sunk = true;
        return true;
      }
    }
    return false;
  }

public void getMove(int x, int y) {
    if(this.computer == null) 
    checkMove(this.myBoard, this.myShips, x, y);
    else
    checkMove(this.myBoard, this.myShips, x, y);
    if (this.myTurn == -1) 
        return;

    this.myTurn = 1;
    this.status.setText("Status: Waiting for your move.");

}





public void getMove(int x, int y) {
        System.out.println("GETTING MOVE FROM COMPUTER CLASS: ");
        System.out.println("%%%%%%%%%%%%COMPUTER CLASS X COORD FIRST COMES: " + x);
        System.out.println("%%%%%%%%%%%%COMPUTER CLASS Y COORD FIRST COMES: " + y);
        this.computerGameBoard.getMove(x, y); //Gets move from the player from PlayBoard class t through computerGameBoard variable.
        int XCoord = this.compMoves[this.numMove][0];
        int YCoord = this.compMoves[this.numMove][2];
         System.out.println("!@#*(!@(#&*!@*&#!@*(#*(!@&*$^!@&$^#!@&*(#@!#!@");
           for(int[] zz : compMoves) {
                System.out.println("");
                System.out.println(Arrays.toString(zz));
            }
        System.out.println("XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXCOORD: " + XCoord);
        System.out.println("YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYCOORD: " + YCoord);
        this.playerGameBoard.getMove(XCoord, YCoord);
        this.computerGameBoard.makeMove(XCoord, YCoord);
        this.numMove = numMove + 1;
    }

 public void makeMove(int x, int y)
  {
      System.out.println("MAKING MOVE WITH COORDS:   X " + x + "  Y " +y );
    checkMove(this.opponentBoard, this.opponentShips, x, y);
    if (this.myTurn == -1)
      return;
    this.myTurn = 0;
    this.status.setText("Status: Waiting for opponent move");

    if (this.computer != null)
      this.computer.getMove(x, y);
  }

Answer 1

你的问题是一个常见的问题，我看到别人第一次使用对象数组。当你创建一个对象数组时，数组被创建了，但是数组的单个元素是null，即它们不引用对象。创建数组之后，需要创建实际对象:

Ship inShips[] = new Ship[5];
for(int i = 0; i < inShips.length; ++i)
    inShips[i] = new Ship();

当你在一个对象上调用一个方法时，在引用后面需要有一个真正的对象。如果引用是null，则它不引用对象。由于您正在调用null引用上的方法，因此您的程序崩溃并且您得到NullPointerException。