How is this private variable accessible?

Question

How is the compiler not complaining when I write the following code?

public class MyClass  {     private int count;      public MyClass(int x){         this.count=x;     }      public void testPrivate(MyClass o){         System.out.println(o.count);     }    } 

Even though it is an instance of the same class in which testPrivate is written, shouldn't it give a compilation error at System.out.println(o.count)? After all, I am trying to access a private variable directly.
The code even runs fine.

Answer 1

A private member is accessible from any method within the class in which it is declared, regardless of whether that method accesses its own (this) instance's private member or some other instance's private member.

This is stated in JLS 6.6.1:

...Otherwise, if the member or constructor is declared private, then access is permitted if and only if it occurs within the body of the top level class (§7.6) that encloses the declaration of the member or constructor.

This feature of Java allows you to write methods that accept an instance of the class as an argument (for example - clone(Object other), compareTo(Object other)) without relying on the class having non private getters for all the private properties that need to be accessed.

Answer 2

Private fields are private to the class as a whole, not just to the object.

Other classes do not know that MyClass has a field called count; however, A MyClass object knows that another MyClass object has the count field.