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i am having a problem on my Battleship project. The problem is at Move checking and making.

When i click at enemy board and computer's turn comes I get null pointer exception at hit = inShips[i].checkMove(x, y); at checkMove method.

Here is the full project: http://db.tt/V6YiTJVw (You need to change image paths at selectionPanel and selectionFrame classes)

Thanks for your help

 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);
  }
4

1 回答 1

2

您的问题是我在其他人第一次使用对象数组时看到的常见问题。创建对象数组时，会创建数组，但数组的各个元素是null，即它们不引用对象。创建数组后，您需要创建真实对象：

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

当您在对象上调用方法时，引用后面需要有一个真实的对象。如果引用是null，则它不引用对象。由于您在引用上调用方法null，因此您的程序崩溃并且您得到一个NullPointerException.

于 2013-04-24T18:25:22.787 回答