I have the following code:
ArrayList <String> entries = new ArrayList <String>();
entries.add("0");
entries.add("1");
entries.add("2");
entries.add("3");
String firstNotHiddenItem = entries.stream()
.filter(e -> e.equals("2"))
.findFirst()
.get();
I need to know what is the index of that first returned element, since I need to edit it inside of entries ArrayList. As far as I know get() returns the value of the element, not a reference. Should I just use
int indexOf(Object o)
instead?
You can't in a straightforward way - streams process elements without context of where they are in the stream.
However, if you're prepared to take the gloves off...
int[] position = {-1};
String firstNotHiddenItem = entries.stream()
.peek(x -> position[0]++) // increment every element encounter
.filter("2"::equals)
.findFirst()
.get();
System.out.println(position[0]); // 2
The use of an int[], instead of a simple int, is to circumvent the "effectively final" requirement; the reference to the array is constant, only its contents change.
Note also the use of a method reference "2"::equals instead of a lambda e -> e.equals("2"), which not only avoids a possible NPE (if a stream element is null) and more importantly looks way cooler.
A more palatable (less hackalicious) version:
AtomicInteger position = new AtomicInteger(-1);
String firstNotHiddenItem = entries.stream()
.peek(x -> position.incrementAndGet()) // increment every element encounter
.filter("2"::equals)
.findFirst()
.get();
position.get(); // 2