Tuesday, 21 July 2015

Java 8 Lambda overhead

Intro

This is a follow-up to an earlier post where I was speculating that Java's Just In Time compilation may have been causing significant performance differences when some code was being exercised more than one or two times.

Here is a snippet of the code which I would like to focus on:

int anIndex = Collections.binarySearch(sorted, target, 
(o1, o2) -> o1.compareTo(o2)
);

The title of this post should have given away that the lambda expression made the performance take a hit until something kicked in and probably replace the lambda setup in each loop iteration with a single instance.

Alternatives

Comparator intComparator = Integer::compareTo;
int anIndex = Collections.binarySearch(sorted, target, intComparator);

Also uses some Java 8 magic and performs slowly.

Comparator intComparator = new Comparator() {
    @Override    public int compare(Integer o1, Integer o2) {
        return o1.compareTo(o2);    }
};int anIndex = Collections.binarySearch(sorted, target, intComparator);

Doesn't use any lambda expressions and performs quickly.

The final, slightly embarrassing example:

int anIndex = Collections.binarySearch(sorted, target);

So, I didn't even need to define the method for the comparison.

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