Difference between Iterator and Spliterator in Java8

by

An Iterator is a simple representation of a series of elements that can be iterated over.

eg:

 List<String> list = Arrays.asList("Apple", "Banana", "Orange");
 Iterator<String> i = list.iterator();
 i.next();
 i.forEachRemaining(System.out::println);

#output
Banana
Orange

A Spliterator can be used to split given element set into multiple sets so that we can perform some kind of operations/calculations on each set in different threads independently, possibly taking advantage of parallelism. It is designed as a parallel analogue of Iterator. Other than collections, the source of elements covered by a Spliterator could be, for example, an array, an IO channel, or a generator function.

There are 2 main methods in the Spliterator interface.

– tryAdvance() and forEachRemaining()

With tryAdvance(), we can traverse underlying elements one by one (just like Iterator.next()). If a remaining element exists, this method performs the consumer action on it, returning true; else returns false.

For sequential bulk traversal we can use forEachRemaining():

 List<String> list = Arrays.asList("Apple", "Banana", "Orange");
 Spliterator<String> s = list.spliterator();
 s.tryAdvance(System.out::println);
 System.out.println(" --- bulk traversal");
 s.forEachRemaining(System.out::println);

 System.out.println(" --- attempting tryAdvance again");
 boolean b = s.tryAdvance(System.out::println);
 System.out.println("Element exists: "+b);

Output:

Apple
 --- bulk traversal
Banana
Orange
 --- attempting tryAdvance again
Element exists: false

– Spliterator trySplit()

Splits this spliterator into two and returns the new one:

  List<String> list = Arrays.asList("Apple", "Banana", "Orange");

  Spliterator<String> s = list.spliterator();
  Spliterator<String> s1 = s.trySplit();

  s.forEachRemaining(System.out::println);
  System.out.println("-- traversing the other half of the spliterator --- ");
  s1.forEachRemaining(System.out::println);

Output:

Banana
Orange
-- traversing the other half of the spliterator ---
Apple

An ideal trySplit method should divide its elements exactly in half, allowing balanced parallel computation.

The splitting process is termed as ‘partitioning’ or ‘decomposition’ as well.

Leave a Comment

tech