How Can I Efficiently Iterate Through a Java 8 Stream and Access Indices?

Efficient Stream Iteration with Indices in Java 8

Introduction

Accessing indices while iterating over streams in Java 8 can be a tedious task, especially when compared to its LINQ counterpart. This article explores concise and efficient ways to achieve this functionality.

The Intermediate Solution

One approach is to combine a stream of indices with the stream of elements, using the zip method. However, this method has been either moved or removed, making this approach less accessible.

The Cleanest Way: From Indices

A more streamlined solution is to start with a stream of indices. This can be achieved using IntStream.range() and provides a convenient starting point for filtering and mapping operations:

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());

Using a Mutable Index

Another alternative is to maintain an ad hoc counter using a mutable object like an AtomicInteger. This approach resembles traditional for loops:

String[] names = {"Sam", "Pamela", "Dave", "Pascal", "Erik"};
AtomicInteger index = new AtomicInteger();
List<String> list = Arrays.stream(names)
                          .filter(n -> n.length() <= index.incrementAndGet())
                          .collect(Collectors.toList());

Caution for Parallel Streams

It's important to note that using this latter method on parallel streams can introduce issues, as items may not be processed in order.

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