Functional Programming - Infinite Streams

Collections are in-memory data structure which have all the elements present in the collection and we have external iteration to iterate through collection whereas Stream is a fixed data structure where elements are computed on demand and a Stream has inbuilt iteration to iterate through each element. Following example shows how to create a Stream from an array.

int[] numbers = {1, 2, 3, 4};
IntStream numbersFromArray = Arrays.stream(numbers);

Above stream is of fixed size being built from an array of four numbers and will not return element after 4th element. But we can create a Stream using Stream.iterate() or Stream.generate() method which can have lamdba expression will pass to a Stream. Using lamdba expression, we can pass a condition which once fulfilled give the required elements. Consider the case, where we need a list of numbers which are multiple of 3.

Example - Infinite Stream

import java.util.stream.Stream;

public class FunctionTester {    
   public static void main(String[] args) {
      //create a stream of numbers which are multiple of 3 
      Stream<Integer> numbers = Stream.iterate(0, n -> n + 3);

      numbers
         .limit(10)
         .forEach(System.out::println);
   }   
}

Output

0
3
6
9
12
15
18
21
24
27

In order to operate on infinite stream, we've used limit() method of Stream interface to restrict the iteration of numbers when their count become 10.