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).