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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().

Practice 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));.

Starter code

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

public class Main {
    public static void main(String[] args) {
        // Declare List<String>, add three names, get Spliterator, print with forEachRemaining

    }
}

Sample solution

Main.java
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));
    }
}

Expected output

Ayşe
Alex
Mehmet

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Complete the advance call

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

Explanation: tryAdvance runs the action on the next element if present.

2 What does Spliterator.trySplit do?

  • Deletes all elements
  • Returns only the first element
  • Returns an empty Spliterator
  • Splits the Spliterator in two Correct answer

Explanation: trySplit partitions the Spliterator into two for parallel processing.

3 Match the Spliterator methods

Term Meaning
tryAdvance Processes one element
forEachRemaining Bulk processes the rest
trySplit Splits in two
estimateSize Estimates remaining count

All lessons in Intermediate

1 Classes

  1. class
  2. Attributes
  3. Methods
  4. new
  5. toString
  6. Summary - Classes

2 Constructor

  1. Constructor basics
  2. Parameterized constructor
  3. Constructor overloading
  4. this()
  5. Default constructor
  6. Summary - Constructor

3 Inheritance

  1. extends
  2. super
  3. Method overriding
  4. Object class
  5. final class and method
  6. Summary - Inheritance

4 Project: Library

  1. Class design
  2. Book model
  3. Member management
  4. Borrow flow
  5. Putting it together

5 Encapsulation

  1. private fields
  2. Getter
  3. Setter
  4. Package-private
  5. Record
  6. Summary - Encapsulation

6 Static

  1. static fields
  2. static methods
  3. static block
  4. Class variables
  5. instanceof
  6. Summary - Static

7 Constants

  1. static final
  2. Uppercase convention
  3. Constants with enum
  4. Interface constants
  5. Math constants
  6. Summary - Constants

8 Project: Quiz app

  1. Quiz model
  2. Adding questions
  3. Running the quiz
  4. Score calculation
  5. Putting it together

9 Interface

  1. interface
  2. implements
  3. default methods
  4. static methods
  5. Multiple interfaces
  6. Summary - Interface

10 Abstract class

  1. abstract class
  2. abstract methods
  3. Abstract and concrete
  4. Abstract vs interface
  5. Sealed class
  6. Summary - Abstract class

11 Polymorphism

  1. Polymorphism basics
  2. Dynamic binding
  3. Override rules
  4. Abstract reference
  5. Pattern matching
  6. Summary - Polymorphism

12 Project: Blog app

  1. Model design
  2. Blog class
  3. Adding comments
  4. Search and filter
  5. Putting it together

13 File I/O

  1. File class
  2. FileReader and FileWriter
  3. BufferedReader
  4. PrintWriter
  5. try-with-resources
  6. Summary - File I/O

14 Serialization

  1. Jackson ObjectMapper
  2. readValue
  3. writeValueAsString
  4. JsonProperty
  5. List and Map serialization
  6. Summary - Serialization

15 Generics

  1. Generic class
  2. Generic method
  3. Bounded type
  4. Wildcard
  5. Type erasure
  6. Summary - Generics

16 Generic collections

  1. List<E>
  2. Map<K,V>
  3. Set<E>
  4. Queue and Deque
  5. Collections class
  6. Summary - Generic collections

17 Iterator

  1. Iterator
  2. remove
  3. ListIterator
  4. Iterable
  5. Spliterator
  6. Summary - Iterator

18 Lambda expressions

  1. Lambda basics
  2. Parameterized lambda
  3. Method reference
  4. forEach with lambda
  5. Comparator with lambda
  6. Summary - Lambda expressions

19 Stream API basics

  1. stream()
  2. filter
  3. map
  4. forEach and count
  5. collect toList
  6. Summary - Stream API basics

20 Intermediate final

  1. Project design
  2. OOP model
  3. Stream layer
  4. File I/O
  5. Putting it together