是否在编译器优化的同一语句中多次调用同一方法？

Question

Let's say I do something like this in Java 8 (Android specifically)

String name = someObject.getName() != null ? someObject.getName() : "null";

and the method getName() might have a lot of calls to other methods to resolve the name. Also suppose I'm calling this code quite often.

Would it be better, performance wise, to do something like this instead?

String name = someObject.getName();
name = name != null ? name : "null";

Answer 1

This looks like an optimization possible, called CSE ; a JVM AFAIK does that (but not sure about Android).

But this highly depends on what getName does, if it allocates internally other objects and does some other things. Unfortunately I can't even tell how to prove me wrong or right here (might need to investigate); honestly I have a habit of doing this myself. For example:

for(int i=0;i<list.size();++i){

}

I try to always extract the int size = list.size() before the loop; even if this in my understanding is subject to scalar replacement optimization.

Answer 2

The second version is calling getName one time, while the first, in case is not null, it's calling that 2 times... so if it is very heavy, the second version is better.

As Arnaud said, you have to consider if the value can change between the two calls: in this case you will get a performance boost, but a risk to get an "old" value.