Does declaring a separate variable and then referencing it cost more space than to set the reference to the new variable?

Question

I can't find anything that is a direct answer to this question but if I am mistaken please link the right question.

Essentially, I'm asking whether there are any disadvantages of this:

MyObject myObject = new MyObject();
this.classReference = myObject;

as compared to this:

this.classReference = new MyObject();

My guess is that differences would be negligible after the code is compiled to bytecode.

The bytecode is different, but the JIT compiler will eliminate the difference. — Andreas, Sep 07 '20 at 21:32
"*Essentially, I'm asking whether there are any disadvantages of this*" - You create an unnecessary stack variable. But the JIT compiler may or may not optimize this out. — Turing85, Sep 07 '20 at 21:32
See [What does a just-in-time (JIT) compiler do?](https://stackoverflow.com/questions/95635/what-does-a-just-in-time-jit-compiler-do) — Turing85, Sep 07 '20 at 21:34
hey @Andreas could you post your version of the answer? youre the first one to actually answer my question of whether some sort of compiler would make the difference negligible — notacorn, Sep 12 '20 at 15:33

score 3 · Answer 1 · answered Sep 07 '20 at 21:43

In this:

MyObject myObject = new MyObject();
this.classReference = myObject;

you have two variables holding a reference to one object. It is important to understand that 'myObject' is not 'an object', it holds a reference to an object. 'new' returns a reference, the reference is stored in `myObject', and copied to 'classReference'.

(By the way, your variable seems misnamed -- it is not a reference to a class, it is a reference to an object, an instance of a class.)

So the only difference between the above and this:

this.classReference = new MyObject();

is that in the former case, there was space allocated on the stack for a local variable (but the allocation was probably in the method prologue, so takes no extra time), and then you need to copy the reference somewhere else. The extra overhead is very very small.

This is assuming that the compiler doesn't optimize away 'myObject' in the first place.

Does declaring a separate variable and then referencing it cost more space than to set the reference to the new variable?

1 Answers1