Question

How can I pass an array by reference in Java? For instance I need to do some operations on the arrays A and B and populate the array C which should be available to the caller.

  public boolean Operate(int[] A, int[] B, int[] C)
  {
     //Write into the empty array C by manipulating values of A and B  and it should be accessible to caller
  }

I read that unlike C#, pass by reference is not there in Java. In that case what is the best way to do this.

Answer 1

You are getting the term ‘pass by reference‘ confused with ‘pass (the reference of an object) by value‘ (which is what Java and C#, without out/ref do). In the above, if the contents of A, B or C are changed, they are changed because NO NEW OBJECT IS CREATED/CLONED/DUPLICATED when they are passed to the method. In C#, ‘ref’ and ‘out’ how one uses ‘pass by reference‘. Note that when ‘pass by reference‘ is used, assigning to a variable changes the value of the variable pass in by the caller (this is not possible in Java).

See Wiki: Evaluation Strategies.

Edit: If you really wish to follow this approach, remember that the calling convention does not dictate object mutability. Consider the following:

void merge(int[] A, int[] B, int[][] C) {
    int[] t = internalMerge(A, B);
    C[0] = t;
}
int[][] icky = new int[1][0];
merge(..., ..., icky);
int[] r = icky[1];

However, I would simply structure the code better. There is very little reason to use this approach and it introduces more side-effects and state mutations. As you can see, there is already a run-time error that the above code introduces. As others have suggested, why not simply return the more appropriate value?