Do objects encapsulate data so that not even other instances of the same class can access the data?

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I don’t tend to think of it in terms of one object having access to another, but rather what code has access to what data within an object.

In Java (and C#, btw) code within a class has access to the private members of any object of the same class. Then you’ve got package/assembly access and public access.

The tricky one is protected access, which is sort of access to code in subclasses – but it depends on the target object: you’re only allowed to access protected members of an object if it’s an instance of the same type as the location of the code, or some subclass – even if it’s being exposed by a parent class. So for instance, suppose you had:

class Parent
{
    protected int x;
}

class Child1 extends Parent
class Child2 extends Parent
class Grandchild extends Child1

Then within the Child1 code, you can access Parent.x only for objects which are known (at compile-time) to be instances of Child1 or Grandchild. You couldn’t, for instance, use new Parent().x or new Child2().x.

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