Java，关于使用对象数组的 NullPointerException

Question

这是代码示例。我想创建一个一维对象数组，给它们赋值，在其他方法中使用它，然后将它作为二维数组打印出来。

起初我想打印起始板，但是当我尝试循环遍历数组时出现 NullPointException。二维数组是一个 6x6 矩阵。

public class Field{
    int diceCount, playerNumber;

    //get and set methods etc.
}

public class Board{
    public Field[] board = new Field[36];

    public void boardBuilder(){
        for(int i = 0; i < board.length; i++){
            board[i] = new Field();
            //give value to the Fields      
        }
    }
}

public class IoMethods{
    public Board board = new Board();

    public void boardPrintOut(){
        int helper;
        for(int i = 0; i < 6; i++){
            for(int j = 0; j < 6; j++){
                //The next line is where it gets the Exception
                helper = board.board[i*6 + j].getPlayerNumber();

                //print part
            }
        }
    }
}

Answer 1

您没有构建电路板。在遍历成员之前执行 board.boardBuilder()

board.boardBuilder()
for(int i = 0; i < 6; i++){
    for(int j = 0; j < 6; j++){
        //The next line is where it gets the Exception
        helper = board.board[i*6 + j].getPlayerNumber();
            //print part
    }
}