Prior to JDK 8, collections can only be managed through iterators with the use of for, foreach or while loops. It means that we instruct a computer to execute the algorithm steps. int sum(List<Integer> list) { Iterator<Integer> intIterator = list.iterator(); int sum = 0; while (intIterator.hasNext()) { int number = intIterator.next(); if (number > 5) { sum += number; } } return sum; } The above approach has the following tailbacks: