Efficiency of having logic in-line vs calling a method?

Question

I currently have a disagreement going on with my 2nd year JAVA professor that I'm hoping y'all could help solve:

The code we started with was this:

   public T peek()
   {
       if (isEmpty())
       .........
   }
   public boolean isEmpty() 
   {
       return topIndex<0;
   }

And she wants us to remove the isEmpty() reference and place its code directly into the if statement (i.e. change the peek method contents to: if(topIndex<0).......) to "Make the code more efficient". I have argued that a) the runtime/compile time optimizer would most likely have inlined the isEmpty() call, b) even if it didn't, the 5-10 machine operations would be negligible in nearly every situation, and c) its just bad style because it makes the program less readable and less changeable.

So, I guess my question is: Is there any runtime efficiency gained by inlineing logic as opposed to just calling a method? I have tried simple profiling techniques (aka long loop and a stopwatch) but tests have been inconclusive.

EDIT:

Thank you everyone for the responses! I appreciate you all taking the time. Also, I appreciate those of you who commented on the pragmatism of arguing with my professor and especially doing so without data. @Mike Dunlavey I appreciate your insight as a former professor and your advice on the appropriate coding sequence. @ya_pulser I especially appreciate the profiling advice and links you took the time to share.

Answer 1

You are correct in your assumptions about java code behaviour, but you are impolite to your professor arguing without data :). Arguing without data is pointless, prove your assumptions with measurements and graphs.

You can use JMH ( http://openjdk.java.net/projects/code-tools/jmh/ ) to create a small benchmark and measure difference between:

• inlined by hand (remove isEmpty method and place the code in call place)
• inlined by java jit compiler (hotspot after 100k (?) invocations - see jit print compilation output)
• disabled hotspot inlining at all

Please read http://www.oracle.com/technetwork/java/whitepaper-135217.html#method

Useful parameters could be:

• -Djava.compiler=NONE
• -XX:+PrintCompilation

Plus each jdk version has it's own set of parameters to control jit.

If you will create some set of graphics as results of your research and will politely present them to the professor - I think it will benefit you in future.

I think that https://stackoverflow.com/users/2613885/aleksey-shipilev can help with jmh related questions.

BTW: I had great success when I inlined plenty of methods into a single huge code loop to achieve maximum speed for neural network backpropagation routine cause java is (was?) too lazy to inline methods with methods with methods. It was unmaintainable and fast :(.