Question

Say for example I have a class called Phone.

What is the difference between:

Phone p;

and

Phone p = new Phone(200) //(200 is the price of the phone).

and

new Phone(200)

I’ve googled and even tried it on Eclipse but can’t figure it out.

Answer 1

Phone p; only declares a reference handler p which doesn’t point anywhere (it is a not initialized and cannot be used until you assign something to it [thanks @Anthony]).

Phone p = new Phone(200); declares a reference handler p which points to a newly created Phone object (initialized with Phone(200)).

new Phone(200) creates a new Phone object, but since no reference to it is stored anywhere, it becomes immediately eligible for garbage collection (unless its constructor stores a reference somewhere, that is).

_{(Note that in Java, all “variables” whose type is a reference-type are really reference handlers. Only variables of value-type contain values directly. Since Phone is a reference-type (it’s a class), Phone p is always a “reference to a Phone“.)}