Convert Iterator to Iterable in Java

Given an Iterator, the task is to convert it into Iterables in Java.

Examples:

Input: Iterator = {1, 2, 3, 4, 5}
Output: {1, 2, 3, 4, 5}

Input: Iterator = {'G', 'e', 'e', 'k', 's'}
Output: {'G', 'e', 'e', 'k', 's'}

Below are the various ways to do so:

• By overriding the abstract method Iterable.iterator():
  1. Get the Iterator.
  2. Override the Iterable.iterator() method and get the iterable.
  3. Return the Iterable.

  Below is the implementation of the above approach:

  // Java program to get a Iterable
  // from a given Iterator
  
  import java.util.*;
  
  class GFG {
  
      // Function to get the Spliterator
      public static <T> Iterable<T>
      getIterableFromIterator(Iterator<T> iterator)
      {
          return new Iterable<T>() {
              @Override
              public Iterator<T> iterator()
              {
                  return iterator;
              }
          };
      }
  
      // Driver code
      public static void main(String[] args)
      {
  
          // Get the Iterator
          Iterator<Integer>
              iterator = Arrays.asList(1, 2, 3, 4, 5)
                             .iterator();
  
          // Get the Iterable from the Iterator
          Iterable<Integer>
              iterable = getIterableFromIterator(iterator);
  
          // Print the elements of Iterable
          iterable.forEach(System.out::println);
      }
  }
  Output:
  
  

  1
  2
  3
  4
  5
  

• Using Java 8 lambda expression:
  1. Get the Iterator.
  2. Convert the iterator to iterable using Lambda Expression.
  3. Return the Iterable.

  Below is the implementation of the above approach:

  // Java program to get an Iterable
  // from a given Iterator
  
  import java.util.*;
  
  class GFG {
  
      // Function to get the Spliterator
      public static <T> Iterable<T>
      getIterableFromIterator(Iterator<T> iterator)
      {
          return () -> iterator;
      }
  
      // Driver code
      public static void main(String[] args)
      {
  
          // Get the Iterator
          Iterator<Integer>
              iterator = Arrays.asList(1, 2, 3, 4, 5)
                             .iterator();
  
          // Get the Iterable from the Iterator
          Iterable<Integer>
              iterable = getIterableFromIterator(iterator);
  
          // Print the elements of Iterable
          iterable.forEach(System.out::println);
      }
  }
  Output:

  1
  2
  3
  4
  5
  

• Using Spliterators:
  1. Get the Iterator.
  2. Convert the iterator to Spliterator using Spliterators.spliteratorUnknownSize() method.
  3. Convert the Spliterator into Sequential Stream using StreamSupport.stream() method.
  4. Collect the elements of the Sequential Stream as an Iterable using collect() method.
  5. Return the Iterable.

  Below is the implementation of the above approach:

  // Java program to get a Iterable
  // from a given Iterator
  
  import java.util.*;
  import java.util.stream.Collectors;
  import java.util.stream.StreamSupport;
  
  class GFG {
  
      // Function to get the Spliterator
      public static <T> Iterable<T>
      getIterableFromIterator(Iterator<T> iterator)
      {
          return StreamSupport
  
              // Convert the iterator into a Spliterator
              // and then into a sequential stream
              .stream(Spliterators.spliteratorUnknownSize(iterator, 0),
                      false)
  
              // Convert the stream to an iterable
              .collect(Collectors.toList());
      }
  
      // Driver code
      public static void main(String[] args)
      {
  
          // Get the Iterator
          Iterator<Integer>
              iterator = Arrays.asList(1, 2, 3, 4, 5)
                             .iterator();
  
          // Get the Iterable from the Iterator
          Iterable<Integer>
              iterable = getIterableFromIterator(iterator);
  
          // Print the elements of Iterable
          iterable.forEach(System.out::println);
      }
  }
  Output:

  1
  2
  3
  4
  5