如何从 Java 中的子类访问私有数组？

Question

I know its not possible to directly call private array's from within a subclass but I still need to someway to access it so what's the best way to go about this? Right now I have a class for my main method, random array, player array and a fourth class which I want to use to compare the two arrays.

So far I have tried to make a getter method which just returns the array and then I would call that getter method from the compare class. This failed so then I tried to make a basic for loop would return each value in that array but this also does not work. So my question is how can I get the the values of a private array into a subclass?

Here is one of my attempts which just prints 0 0 0 0

    public class test {
      public static void main(String[] args) {
      Scanner console = new Scanner(System.in);

      PlayerArray player = new PlayerArray(console);

      testArray test = new testArray();
      test.printArray();
    }


    class PlayerArray extends RandomArray {
       private int[] playerArray = new int[4];

       public PlayerArray() {
       }

       public PlayerArray(Scanner console) {
           System.out.println();
           System.out.println("Enter 4 numbers you wish to guess: ");
           for(int i=0; i<playerArray.length; i++) {
              playerArray[i] = console.nextInt();
           }
       }

      public int[] getPlayerArray() {
         return playerArray;
      }
    }


  class testArray extends PlayerArray {

    public void testArray() {
    }

    public void printArray() {
        System.out.println(getPlayerArray());
        for (int i = 0; i < 4; i++) {
            System.out.print(getPlayerArray()[i]);
        }

    }
 }

Answer 1

You're doing it.

However, public void testArray() does nothing - did you intend to make a constructor? Those don't have a return type, so, just public testArray .

Because you did not write a constructor, java made one for you. It's equivalent to:

public testArray() {
    super();
}

as in, it calls the PlayerArray constructor that doesn't do anything, thus resulting in the playerArray holding 4x a 0 value. If you want something else, well, that Scanner reference isn't going to appear out of thin air, so:

public testArray(Scanner console) {
    super(scanner);
}

to invoke 'the right one'.

NB: It should be TestArray , and making arrays visible to externals is bad as making them public; you have no control over it, and anybody you give it to can change it with eg getPlayerArray()[i] = 10; . Generally, use Lists ( java.util.List ) and such instead of arrays.

Answer 2

  PlayerArray player = new PlayerArray(console);

Here you create an instance of PlayerArray which takes in the console and populating the internal array.

  testArray test = new testArray();
  test.printArray();

Here you create a NEW instance of testArray where the internal array hasn't been populated.

For it to print the correct values you need to copy the printArray() method to the Player class and call the printArray() method on the player instance.

  player.printArray();

and just delete the testArray() instance from the Main method. It serves no purpose here.

Alternatively you can add a constructor in the Player class that takes in a Console and passes it to the Super via super(console);