Best Practice for Returning Object References

Question

Consider this code snippet:

class MyClass{
    private List myList;
    //...
    public List getList(){
        return myList;
    }
}

As Java passes object references by value, my understanding is that any object calling getList() will obtain a reference to myList, allowing it to modify myList despite it being private. Is that correct?

And, if it is correct, should I be using

return new LinkedList(myList);

to create a copy and pass back a reference to the copy, rather than the original, in order to prevent unauthorised access to the list referenced bymyList?

Answer 1

I do that. Better yet, sometimes I return an unmodifiable copy using the Collections API.

If you don't, your reference is not private. Anyone that has a reference can alter your private state. Same holds true for any mutable reference (e.g., Date).

Answer 2

It depends on what you want.

Do you want to expose the list and make it so people can edit it?

Or do you want to let people look at it, but not modify it?

There is no right or wrong way in this case. It just depends on your design needs.