Convert Iterator to List

Exploiting libraries for smooth conversions

Thanks to the rich ecosystem of Java, we have access to a variety of libraries that can expedite certain processes. For instance, when converting an Iterator to a List, Guava and Apache Commons Collections can be your best friends.

For instance, in Guava, we can achieve the conversion like so:

Iterator<T> iterator = // your iterator;
List<T> list = Lists.newArrayList(iterator);
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And if you are looking for an immutable list, here's how:

List<T> immutableList = ImmutableList.copyOf(iterator);
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The methods Lists.newArrayList() and ImmutableList.copyOf() are specifically engineered for these scenarios, and offer performance-optimized solutions.

Apache Commons Collections provides another user-friendly utility:

Iterator<T> iterator = // your iterator;
List<T> list = IteratorUtils.toList(iterator);
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But remember, IteratorUtils.toList() lacks generic support. So watch out in type-sensitive situations!

Incorporating Java 8 methods for elegance

Java 8 introduced us to new methods such as forEachRemaining that make transforming Iterator to List a piece of cake. Here is how you can quickly populate an existing mutable List:

List<Type> list = new ArrayList<>();
iterator.forEachRemaining(list::add);
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The forEachRemaining() method makes short work of processing remaining elements. So bid goodbye to unnecessary boilerplate code!

Traversing from Iterable to List using Spliterator

In certain cases, you might need to transform an Iterable to a List but only have an Iterator to work with. Don't worry, Java 8's Spliterator comes to the rescue:

Iterable<T> iterable = // your iterable;
List<T> list = StreamSupport.stream(iterable.spliterator(), false)
    .collect(Collectors.toList());
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The spliterator() method succeeds in bridging the gap between Iterable and streams, thereby facilitating the conversion.

Portable conversion with generic methods

When you're repeatedly converting Iterators to Lists throughout your codebase, extract the logic into a generic method for higher efficiency and reusability:

public static <T> List<T> iteratorToList(Iterator<T> iterator) {
    //Dude, where's my stream?
    //Oh, here it is!
    return StreamSupport.stream(
        Spliterators.spliteratorUnknownSize(iterator, 0), false)
        .collect(Collectors.toList());
}
//From chaotic iterator to orderly list in one line! 👊
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With this convenient method, you can reuse it across multiple sections of your code.

Warnings and precautions

While converting an Iterator to a List is powerful, be mindful on data loss and performance pitfalls. Ensure you're not throwing out data unintentionally and that your dataset sizes are within acceptable bounds to avoid memory troubles.