What is object reference?

Question

Hi all,
what is object reference? How it works ?
is there any documents location for it?
Thanks

Answer 1

An object reference is a type in Java that holds, conceptually, the address of an object. Any variable you declare will either be of a primitive type (byte, char, short, int, long, float, double, boolan) or of a reference type (anything that you would think of as an "object" type).
A Java reference is conceptually very much like a C pointer, but more limited in what you can do with it--you can't assign arbirary values or do math or cast between reference types an integral types like you can with C pointers.
Any declaration you see in Java--variable, method return type, parameter--that's whose type is not one of the primitives (i.e., it's an "object" type) is a reference.
Foo foo1 = new Foo(); // 1
Foo foo2 = new Foo(); // 2
Foo foo3 = foo1; // 3
foo3 = foo2; //4 foo1, foo2, foo3, foo4 are all variables that hold object references.
At line 1, we create an object of type Foo and stick a reference to that in foo1.
At line 2, we create another Foo and stick a reference to it in foo2.
At line 3, we copy the reference in foo1 into foo3. foo1 and foo3 both refer to the same Foo object.
At line 4, we copy the reference in foo2 into foo3. Now foo2 and foo3 both refer to the same object. This doesn't change either of the Foo objects, and it doesn't change the foo1 reference. It just changes which object foo3 refers to.