Enhanced for loop vs. for loop

Question

i would like to know, if enhanced for loop doesnt allow changes in the elements of the array, that means, it uses less memory, and it is faster?

Answer 1

The first thing to note is that for collections the enhanced for loop uses an Iterator, so if you manually iterate over a collection using an Iterator then you should have pretty much the same performance than the enhanced for loop.

One place where the enhanced for loop is faster than a naively implemented traditional loop is something like this:

LinkedList<Object> list = ...;

// Loop 1:

int size = list.size();

for (int i = 0; i<size; i++) {
Object o = list.get(i);
/// do stuff
}

// Loop 2:

for (Object o : list) {
// do stuff
}

// Loop 3:

Iterator<Object> it = list.iterator();

while (it.hasNext()) {
Object o = it.next();
// do stuff
}

In this case Loop 1 will be slower than both Loop 2 and Loop 3, because it will have to (partially) traverse the list in each iteration to find the element at position i.
Loop 2 and 3, however will only ever step one element further in the list, due to the use of an Iterator. Loop 2 and 3 will also have pretty much the same performance since Loop 3 is pretty much exactly what the compiler will produce when you write the code in Loop 2.

Answer 2

thank you for the explanation!