Convert an Iterator to Iterable in Java

This post will discuss how to convert an iterator to Iterable in Java.

1. Java 7

The Iterable interface declares a single abstract method iterator() that returns an Iterator<T>.

import java.util.Arrays;

import java.util.Iterator;

// Program to convert an iterator to Iterable in Java

class Main

{

public static<T> Iterable<T> iteratorToIterable(Iterator<T> iterator)

{

return new Iterable<T>() {

@Override

public Iterator<T> iterator() {

return iterator;

}

};

}

public static void main(String[] args)

{

Iterator<Integer> iterator = Arrays.asList(1, 2, 3, 4, 5).iterator();

Iterable<Integer> iterable = iteratorToIterable(iterator);

iterable.forEach(System.out::println);

}

Download Run Code

Output:

1
2
3
4
5

2. Java 8 and above

The Iterable is effectively a functional Interface, and converting an Iterator to Iterable can be done very easily with a lambda expression in Java 8 and above, as shown below:

import java.util.Arrays;

import java.util.Iterator;

class Main

{

public static<T> Iterable<T> iteratorToIterable(Iterator<T> iterator) {

return () -> iterator;

}

public static void main(String[] args)

{

Iterator<Integer> iterator = Arrays.asList(1, 2, 3, 4, 5).iterator();

Iterable<Integer> iterable = iteratorToIterable(iterator);

iterable.forEach(System.out::println);

}

Download Run Code

Output:

1
2
3
4
5

3. Converting an `Iterator` to `Spliterators`

The idea is to convert the iterator into a Spliterator using Spliterators.spliteratorUnknownSize() and then create a new sequential stream from Spliterator by using the StreamSupport.stream() method. Finally, we convert the stream to an iterable using a Collector.

import java.util.Arrays;

import java.util.Iterator;

import java.util.Spliterators;

import java.util.stream.Collectors;

import java.util.stream.StreamSupport;

// Program to convert an iterator to Iterable in Java

class Main

{

private static <T> Iterable<T> iteratorToIterable(Iterator<T> iterator)

{

// 1. Convert the Iterator into a Spliterator

// 2. Convert the Spliterator into a sequential stream

// 3. Convert the Stream to an Iterable

return StreamSupport

.stream(Spliterators.spliteratorUnknownSize(iterator, 0),

false)

.collect(Collectors.toList());

}

public static void main(String[] args)

{

Iterator<Integer> iterator = Arrays.asList(1, 2, 3, 4, 5).iterator();

Iterable<Integer> iterable = iteratorToIterable(iterator);

iterable.forEach(System.out::println);

}

Download Run Code

Output:

1
2
3
4
5

That’s all about converting an Iterator to Iterable in Java.

Convert an Iterator to Iterable in Java

1. Java 7

2. Java 8 and above

3. Converting an Iterator to Spliterators

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3. Converting an `Iterator` to `Spliterators`