Object visibility

[Igor Zeta]

Hiall,
I've red the following on a
study note by "Ashraf Fouad Ayoub".
In a true false question.
could you explain me the following sentence:
Objects themselves do not have visibility, only references to the object
In what context?
What do you think it refer to?

[Valentin Crettaz]

It means that when declaring
private Object obj = new Object();
as an instance member of some class, it is the reference variable obj that is private to the class in which it is declared, not the actual Object instance refered to by obj (which is on the heap).
The object instance could be returned by some method in the class but the reference variable itself cannot.

[Tom Adams]

something like this...
The object can be modified by any object reference that can get a hold of it.

class Test {
private StringBuffer sb= new StringBuffer("Test ");
public StringBuffer getSb() { return sb;  }
public void printSb() { System.out.println(sb); }
}
public class Test12 {
public static void main( String[] argv ) {
Test t= new Test();
StringBuffersb= t.getSb();
sb.append("Modified by Test12");
t.printSb();
//System.out.println( t.sb );  compiler error sb has private access
}
}
---------- run ----------
Test Modified by Test12
Output completed (0 sec consumed) - Normal Termination

[Igor Zeta]

Ok Now is better.
So is the same of saying:

An object although private can be updated having copy of its reference?

[Valentin Crettaz]

No! An object cannot be private or protected or whatever access you may want to give it. Only the reference to an object, that is the variable you are using for referencing the object, may have an access modifier.

[Dan Culache]

An object although private can be updated having copy of its reference?

Once you have a reference to this object you want to update it right. In order to update it you must call or access its members. This is when the access modifiers come into play again since you won't be able to call or access members of that object that have restricted access (private, default and you are in another package, protected and you are in another package and not a subclass).