Spliterator

Learn parallel iteration with Spliterator.

The Spliterator<T> interface

Spliterator<T> is an Iterator-like interface introduced in Java 8 designed for parallel traversal. tryAdvance(action) runs the action on the next element if one exists and returns true; otherwise returns false. forEachRemaining(action) processes all remaining elements at once.

trySplit() partitions the Spliterator into two parts to allow parallel processing; this is the basis of parallel streams. estimateSize() estimates the number of remaining elements.

Bulk processing with forEachRemaining

forEachRemaining(action) processes all remaining elements in one call. It is more concise than a while (sp.tryAdvance(action)) loop; Java still walks elements one by one behind the scenes but the code is shorter.

For example you take a Spliterator from a list and write sp.forEachRemaining(s -> System.out.println(s));. The -> token is a lambda expression; it will be detailed in the next group. Spliterator underpins the Stream API; you can also obtain one with list.stream().spliterator().

Exercise Walk the list with a Spliterator

Declare List<String> names = new ArrayList<>();; add "Ayşe", "Alex", "Mehmet". Get Spliterator<String> sp = names.spliterator();. Print all elements in one call with sp.forEachRemaining(s -> System.out.println(s));.

Show example solution

import java.util.List;
import java.util.ArrayList;
import java.util.Spliterator;

public class Main {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();
        names.add("Ayşe");
        names.add("Alex");
        names.add("Mehmet");
        Spliterator<String> sp = names.spliterator();
        sp.forEachRemaining(s -> System.out.println(s));
    }
}

Test yourself

Complete the advance call

while (sp.____(s -> System.out.println(s))) { }

Show answer

while (sp.tryAdvance(s -> System.out.println(s))) { }

What does Spliterator.trySplit do?
- Deletes all elements
- Returns only the first element
- Returns an empty Spliterator
- Splits the Spliterator in two
Show answer

Splits the Spliterator in two — trySplit partitions the Spliterator into two for parallel processing.
Match the Spliterator methods

tryAdvance

Processes one element
forEachRemaining

Bulk processes the rest
trySplit

Splits in two
estimateSize

Estimates remaining count

Next lesson: Summary - Iterator

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