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Program to Iterate over a Stream with Indices in Java 8

Last Updated : 11 Dec, 2018

Given a Stream in Java, the task is to iterate over it with the help of indices.

Input: Stream = [G, e, e, k, s] Output: [0 -> G, 1 -> e, 2 -> e, 3 -> k, 4 -> s] Input: Stream = [G, e, e, k, s, F, o, r, G, e, e, k, s] Output: [0 -> G, 1 -> e, 2 -> e, 3 -> k, 4 -> s, 5 -> F, 6 -> o, 7 -> r, 8 -> G, 9 -> e, 10 -> e, 11 -> k, 12 -> s]

• Method 1: Using IntStream.
  1. Get the Stream from the array using range() method.
  2. Map each elements of the stream with an index associated with it using mapToObj() method
  3. Print the elements with indices
  Java

  // Java program to iterate over Stream with Indices
  
  import java.util.stream.IntStream;
  
  class GFG {
      public static void main(String[] args)
      {
  
          String[] array = { "G", "e", "e", "k", "s" };
  
          // Iterate over the Stream with indices
          IntStream
  
              // Get the Stream from the array
              .range(0, array.length)
  
              // Map each elements of the stream
              // with an index associated with it
              .mapToObj(index -> String.format("%d -> %s", 
                                         index, array[index]))
  
              // Print the elements with indices
              .forEach(System.out::println);
      }
  }
  

  Output:

  0 -> G
  1 -> e
  2 -> e
  3 -> k
  4 -> s
  

• Method 2: Using AtomicInteger.
  1. Create an AtomicInteger for index.
  2. Get the Stream from the array using Arrays.stream() method.
  3. Map each elements of the stream with an index associated with it using map() method where the index is fetched from the AtomicInteger by auto-incrementing index everytime with the help of getAndIncrement() method.
  4. Print the elements with indices.
  Java

  // Java program to iterate over Stream with Indices
  
  import java.util.stream.IntStream;
  import java.util.*;
  import java.util.concurrent.atomic.AtomicInteger;
  
  class GFG {
      public static void main(String[] args)
      {
  
          String[] array = { "G", "e", "e", "k", "s" };
  
          // Create an AtomicInteger for index
          AtomicInteger index = new AtomicInteger();
  
          // Iterate over the Stream with indices
          Arrays
  
              // Get the Stream from the array
              .stream(array)
  
              // Map each elements of the stream
              // with an index associated with it
              .map(str -> index.getAndIncrement() + " -> " + str)
  
              // Print the elements with indices
              .forEach(System.out::println);
      }
  }
  

  Output:

  0 -> G
  1 -> e
  2 -> e
  3 -> k
  4 -> s
  

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