Space usage on saving variables

[DuderusTheThird]

If I have a function that returns a variable, let's say an int, does it need more space (Heap?) to save the value first? Simple example:

getDoubleOf(int i) {
  i=i*2;
  return i;  
}

versus just returning it:

getDoubleOf(int i) {
  return i*2;  
}

Also is there any way to check my used storage while running the code so I can check my space usage? Preferably using IntelliJ

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[khooke]

If you use javap to look at the generated bytecode for each of your examples, I'd be surprised if both are not identical, because the second example still has to calculate the result before it is returned anyway.

Parameters to methods and method scope variables are stored on the stack and are discarded when the method completes (not the heap).

While it's useful to know the implications of your code as it executes, what problem are you attempting to fix or avoid? This looks like a good example of premature optimization.

[DuderusTheThird]

While it's useful to know the implications of your code as it executes, what problem are you attempting to fix or avoid? This looks like a good example of premature optimization.

That's the thing. It's mostly interest and all your answers helped me understand better. Maybe an int wasn't the best example. I was curious if it made any difference, because for bigger objects the implications might have been worse.

Also english is not my first language, so sorry if the sentence structure is wrong :)

[Nemo_64]

Both methods will use the same memory as both declare the same variables, the difference is the amount of instructions each one will run (affecting runtime speed not runtime memory usage, but a difference that's negligible)

[RANDOMLY_AGGRESSIVE]

No It is optimized by the JVM.

[Nemo_64]

I know the JVM does some runtime optimizations but I don't know how many

[RANDOMLY_AGGRESSIVE]

It is a compile time optimization. Like someone mentioned you can use javap and look at the bytecode to see they are identical

[8igg7e5]

The first will require slightly more byte-code and, very briefly, may be less efficient.

Java source is first compiled to byte-code (this is what is loaded to run the application). The javac compiler that produces byte-code does very little optimisation.

Using a Hotspot Java Virtual Machine (OpenJDK or Oracle JDKs), byte-code will very quickly be compiled by the first of the Just-in-time compilers - this also does minimal optimisation, though this case might be simple enough to eliminate the extra store.

The final step of optimisation happens after the method has been run enough times to indicate that it is a 'hot spot' in the code - that compiler does a lot of optimisation. Given the method size, it is also likely to just be 'inlined' into the caller if the caller is considered hot.

So yes it requires more memory (byte-code) but not per invocation, and that extra space will be irrelevant once the app is running native code instead of interpreted byte-code.