Question

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Is Java pass by reference?

I have a question about passing by value and passing by reference in java.

I have a “Graph” class that I wrote to display a long array of doubles as a graph, The (simplified) constructor looks like this.

private double[] Values;

public Graph(double[] values) {
   Values = values;
}

The array can be quite long and take up a reasonable amount of memory.

Essentially my question is this: If I call the constructor to create a new graph, will the array “Values” be a copy of the array that’s passed to it, or will it be a reference?

In my mind, Primitives are “pass by value” and Objects are “pass by reference”, which should mean that the array would be a copy. Although I’m aware that this definition is not technically correct.

If I am correct, and the array is a copy, what would be the best way to reduce the amount of memory this class uses, and reference the array from another class?
Would an abstract GetValues() method be a good way of achieving this?

Thanks in advance,

Chris.

Answer 1

While double is a primitive type, double[] is an Object type (array), so, no, the entire array will not be passed to the constructor, instead the array will be passed as “value of a reference”. You will not be able to replace the array inside the constructor, but you could, if you wanted, replace individual values in the array.