不打印二维数组

Question

When I call the printBoard method it doesn't print anything. Could't find out what I wrote wrong How could I fix that if the error is nowhere else.

public class Board {
    private int rows;
    private int cols;
    private char[][] Board = new char[rows][cols];

    public Board(int row, int col) {
        rows = row;
        cols = col;

        for (int i = 0; i < Board.length; i++) {
            for (int j = 0; j < Board[i].length; j++) {
                Board[i][j] = '-';
            }
        }
    }

    public void printBoard() {
        for (int i = 0; i < Board.length; i++) {
            for (int j = 0; j < Board[i].length; j++) {
                System.out.print(Board[i][j]);
                System.out.print("|");
            }
            System.out.println(" ");
        }
    }
}

Answer 1

You do not recreate Board in the constructor when you set rows and cols , the array is initialized with default 0 values.

It should be:

public Board(int row, int col) {
    rows = row;
    cols = col;

    Board = new char[rows][cols]; // <-- reset array
                
    for (int i=0; i<Board.length ; i++) {
        for (int j=0; j<Board[i].length; j++) {
             Board[i][j]='-';
        }
   }
}

You might have assumed that Board array would be initialized with the values set in the constructor, but in fact the constructor is invoked after initializing the instance variables in the order of their appearance in the class definition.