How to get index of findFirst() in java 8?

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

You can get the index of an element using an IntStream like:

int index = IntStream.range(0, entries.size())
                     .filter(i -> "2".equals(entries.get(i)))
                     .findFirst().orElse(-1);

But you should use the List::indexOf method which is the preferred way, because it's more concise, more expressive and computes the same results.