为什么我的二维数组打印全0？

Question

I have a 2-D array named Maze. it is a global variable. I hard coded the data at each position in my setData() method. but when I try to print my array down below it prints all 0s. why is that? thank you.

public class Maze
{
    int [][] maze = new int[4][6];
    public void setData()
    {
        maze[0][0] = 1; maze[0][1] = 0; maze[0][2] = 1; maze[0][3] = 1; maze[0][4] = 0; maze[0][5] = 1;
        maze[1][0] = 0; maze[1][1] = 0; maze[1][2] = 1; maze[1][3] = 0; maze[1][4] = 0; maze[1][5] = 0; 
        maze[2][0] = 1; maze[2][1] = 0; maze[2][2] = 1; maze[2][3] = 0; maze[2][4] = 1; maze[2][5] = 0; 
        maze[3][0] = 0; maze[3][1] = 0; maze[3][2] = 0; maze[3][3] = 0; maze[3][4] = 1; maze[3][5] = 1; 
    }  

    public void printMaze()
    {
        System.out.println("The matrix: ");

        for (int m=0; m<4; m++)
        {
            for (int n=0; n<6; n++)
                System.out.print(maze[m][n]);
            System.out.println();
        }
    }
}

public class MazeTester 
{
    public static void main (String [] args)
    {
        Maze mmgg = new Maze();

        mmgg.printMaze();
    }
}

Answer 1

You need to run setData to put all your values in.

   public static void main (String [] args)
   {
      setData();
      printMaze();
   }

Answer 2

您永远不会调用setData（）方法，因此该数组将充满默认值0。

Answer 3

Your array prints all 0s because you never initialize it (you just declared setData() and you didn't call it), thus its elements get default values which are 0 for int variables.

If you don't want to use the setData() method, you can initialize your array in an init bloc:

     {
          maze[0][0] = 1; maze[0][1] = 0; maze[0][2] = 1; maze[0][3] = 1; maze[0][4] = 0; maze[0][5] = 1;
          maze[1][0] = 0; maze[1][1] = 0; maze[1][2] = 1; maze[1][3] = 0; maze[1][4] = 0; maze[1][5] = 0; 
          maze[2][0] = 1; maze[2][1] = 0; maze[2][2] = 1; maze[2][3] = 0; maze[2][4] = 1; maze[2][5] = 0; 
          maze[3][0] = 0; maze[3][1] = 0; maze[3][2] = 0; maze[3][3] = 0; maze[3][4] = 1; maze[3][5] = 1; 
      }  

In that way, you just have to instantiate your classe Maze and call the method printMaze():

  public static void main ( String[] args ) {

        Maze mmg = new Maze();
        mmg.printMaze ();

       }

Answer 4

Just as jnd said, you will need to invoke the setData() method on your object reference - mmgg, like so:

mmgg.setData();

Also, to answer your question the reason why it prints all 0s; as you have observed is that upon instantiation of the object (this happens via the 'new' operator) the compiler sets your class's member variables to "reasonable" defaults.

Here are the defaults - which explain why your int values from your maze 2D array were zero after your Maze class was instantiated but without calling your setData() method...

1. byte [default = 0]
2. short [default = 0]
3. int [default = 0]
4. long [default = 0L]
5. float [default = 0.0F]
6. double [default = 0.0D]
7. boolean [default = false]
8. char [default = '\']
9. String (or any Object) [default = null]

[NB:- The compiler never assigns a default value to an uninitialized local variable]