Is there a concise way to iterate over a stream with indices in Java 8?

java

stream-engineering

java-8

best-practices

byAnton Shumikhin·Nov 1, 2024

Below is a fast solution for iterating over an array list with indices using IntStream.range:

List<String> list = Arrays.asList("apple", "banana", "cherry");
IntStream.range(0, list.size())
         .forEach(idx -> {
             // One apple a day keeps the ArrayIndexOutOfBoundsException away! 🍎
             System.out.println("Index: " + idx + ", Element: " + list.get(idx));
         });

Take note: this spectacular style can be extended and adapted for streams too, but ensure you're basking in the shades of thread safety when dealing with parallel streams! 😎

Diving into specifics

Mapping with style

Kicking off with mapToObj for those fancy element mappings:

// Look, I got pairs of fancy Index-fancy Fruit! 👒
IntStream.range(0, list.size())
         .mapToObj(idx -> new AbstractMap.SimpleEntry<>(idx, list.get(idx)))
         .forEach(entry -> {
             System.out.println("Index: " + entry.getKey() + ", Element: " + entry.getValue());
         });

Filtering based on indices

Feeling picky? Here's how you use even indices to cherry-pick (pun intended):

IntStream.range(0, list.size())
         .filter(idx -> idx % 2 == 0) // Returns true for even indices
         .forEach(idx -> System.out.println("Element at even index: " + list.get(idx)));

Side effects of parallel streams and mutable objects

Heads up! When you try to use a mutable AtomicInteger to maintain your index in a parallel stream, you're inviting race conditions for a tea party, which is, sadly, a no-go for parallel streams.

Visualizing Stream Iteration with Indices in Java 8

Imagine a Train (🚂) with carriages (🚃) indexed on a track:

IntStream.range(0, list.size())
         .mapToObj(index -> new AbstractMap.SimpleImmutableEntry<>(index, list.get(index)));

Each carriage carries data and its position:

Before: [Data1, Data2, Data3] // 🚂🚃🚃🚃
After:  [(0, Data1), (1, Data2), (2, Data3)] // 🚂🚃0️⃣🚃1️⃣🚃2️⃣

Seat numbers for passengers, simple as that! ✌️

Libraries and solutions

jOOλ for the concise

// Make it fancy with jOOλ 💍
Seq.seq(list.stream())
   .zipWithIndex()
   .forEach(tuple -> System.out.println("Index: " + tuple.v2 + ", Element: " + tuple.v1));

You get an indexed data stream with minimal effort.

Protonpack magic

// A spell from Protonpack 🧙
StreamUtils.zipWithIndex(list.stream())
           .forEach(indexed -> {
               System.out.println("Index: " + indexed.getIndex() + ", Element: " + indexed.getValue());
           });

It's as easy as saying "abracadabra!" 👌

Stay organized

In the football field of code, abstract classes and static methods are your midfielders, they help consolidate, distribute and coordinate your indexed iteration logic.

Turbocharge with BiFunction

Craving more power? Unleash the fury of BiFunction:

// Two heads are better than one! 👥
IntStream.range(0, list.size())
         .mapToObj(idx -> biFunction.apply(idx, list.get(idx)))
         .forEach(System.out::println);

Optimizing the journey

Remember to wear the seatbelt of ORDERED and IMMUTABLE characteristics when you're driving down the Spliterator highway on your way to optimal performance.

Spicing up indexed zipping

Craftsmanship calls for the right tools. Get up and personal with filtering and complex operations using jOOλ. Revel in the delight of having control that's just a method call away!

explain-codes / Java / Is there a concise way to iterate over a stream with indices in Java 8?

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