java - 一个类可以没有构造函数吗？

Question

这是一段代码作为示例，剩下的只是方法(迷宫类在底部)。所以当它被实例化时，使用

Maze labyrinth = new Maze();

和

System.out.println (labyrinth);

这将打印出网格数组。这是合法的吗？我认为所有类都需要构造函数它如何打印出二维网格数组？

迷宫类:

public class Maze
{
    private final int TRIED = 3;
    private final int PATH = 7;
    private int[][] grid = { {1,1,1,0,1,1,0,0,0,1,1,1,1},
                             {1,0,1,1,1,0,1,1,1,1,0,0,1},
                             {0,0,0,0,1,0,1,0,1,0,1,0,0},
                             {1,1,1,0,1,1,1,0,1,0,1,1,1},
                             {1,0,1,0,0,0,0,1,1,1,0,0,1},
                             {1,0,1,1,1,1,1,1,0,1,1,1,1},
                             {1,0,0,0,0,0,0,0,0,0,0,0,0},
                             {1,1,1,1,1,1,1,1,1,1,1,1,1} };

    public String toString ()
    {
        String result = "\n";
        for (int row = 0; row < grid.length; row++)
        {
            for (int column=0; column < grid[row].length; column++)
            result += grid[row][column] + "";
            result += "\n";
        }
        return result;
    }

}

Answer 1

不需要显式定义构造函数；但是，所有的类都必须有构造函数，如果你不提供任何构造函数，将会生成一个默认的空构造函数:

public Maze() {
}

见 Default Constructor .