How to Efficiently Iterate Java 8 Streams with Indices?

Iterating Streams with Indices in Java 8

In Java 8, streams provide a powerful way to process collections of elements. However, iterating over a stream while accessing indices can be challenging.

The provided code snippet demonstrates an elaborate solution using zip and SimpleEntry to pair indices and stream elements. However, is there a more concise approach?

Fortunately, yes. You can start with a stream of indices and filter based on the index by comparing it to the corresponding element's length. Here's an example:

String[] names = {"Sam", "Pamela", "Dave", "Pascal", "Erik"};
IntStream.range(0, names.length)
         .filter(i -> names[i].length() <= i)
         .mapToObj(i -> names[i])
         .collect(Collectors.toList());

Alternative Approach

Alternatively, you can maintain an ad hoc counter using a mutable object like AtomicInteger. However, this method should not be used on parallel streams as it can lead to incorrect results due to out-of-order processing. An example:

AtomicInteger index = new AtomicInteger();
List<String> list = Arrays.stream(names)
                          .filter(n -> n.length() <= index.incrementAndGet())
                          .collect(Collectors.toList());

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