Why does EnumSet have many overloaded “of” methods?

Question

While going through the EnumSet of method, I have seen multiple overloaded implementations of of method:

publ         


        

Answer 1

Because that class was designed by Josh Bloch, and that guy knows how things work. :) Besides creating an array, the varargs method contains the loop, which is more work for the JIT to optimize the code.

For example, if we look at the implementation of the overloaded version with five parameters:

result.add(e1);
result.add(e2);
result.add(e3);
result.add(e4);
result.add(e5);

we notice that it is some kind of an already unrolled loop that could look like:

for (E e : Arrays.asList(e1, e2, e3, e4, e5)) {
   result.add(e);
}

Also, shorter and simpler methods are more likely to be inlined than longer and more complex ones.