I want to convert this while loop to equivalent code using a Java 8 Streams, but I don't know how to both stream the List and remove elements from it.
private List<String> nameList = new ArrayList<>();
while (nameList.size() > 0) {
String nameListFirstEntry = nameList.get(0);
nameList.remove(0);
setNameCombinations(nameListFirstEntry);
}
I guess this will do
nameList.forEach(this::setNameCombinations);
nameList.clear();
In case you don't need the original list anymore, you might as well create a new empty list instead.
Because List#remove(int) also returns the element, you can both stream the list's elements and remove them via a stream:
Stream.generate(() -> nameList.remove(0))
.limit(nameList.size())
.forEach(this::setNameCombinations);
This code doesn't break any "rules". From the javadoc of Stream#generate():
Returns an infinite sequential unordered stream where each element is generated by the provided Supplier. This is suitable for generating constant streams, streams of random elements, etc.
There is no mention of any restrictions on how the supplier is implemented or that is must have no side effects etc. The Supplier's only contract is to supply.
For those who doubt this is "works", here's some test code using 100K elements showing that indeed order is preserved:
int size = 100000;
List<Integer> list0 = new ArrayList<>(size); // the reference list
IntStream.range(0, size).boxed().forEach(list0::add);
List<Integer> list1 = new ArrayList<>(list0); // will feed stream
List<Integer> list2 = new ArrayList<>(size); // will consume stream
Stream.generate(() -> list1.remove(0))
.limit(list1.size())
.forEach(list2::add);
System.out.println(list0.equals(list2)); // always true
parallel(). It is not "illegal", or even mysterious. It is using List#remove() as the stream's Supplier... big deal. Try it yourself if you have doubts.
nameList is made out of 3 elements [a,b,c]; by the same result Im expecting to see these 3 elements in any order (since it's parallel)
setNameCombinations?forEachare allowed to modify the source list, so you're out of luck on failthful conversion.