LongStream flatMap(LongFunction mapper) in Java

LongStream flatMap(LongFunction mapper) returns a stream consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element. This is an intermediate operation. These operations are always lazy. Intermediate operations are invoked on a Stream instance and after they finish their processing, they give a Stream instance as output.

Note : Each mapped stream is closed after its contents have been placed into this stream. If a mapped stream is null, an empty stream is used, instead.

Syntax :

LongStream flatMap(LongFunction<? extends LongStream> mapper)

Parameters :

1. LongStream : A sequence of primitive long-valued elements.
2. LongFunction : A function that accepts an long-valued argument and produces a result.
3. mapper : A stateless function which is applied to each element and the function returns the new stream.

Return Value : LongStream flatMap(LongFunction mapper) returns a stream by a mapped stream using mapping function.

Example 1 : Using LongStream flatMap() to get the cube of elements of LongStream.

// Java code for LongStream flatMap
// (LongFunction mapper) to get a stream
// consisting of the results of replacing
// each element of this stream with the
// contents of a mapped stream
import java.util.*;
import java.util.stream.LongStream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {
        // Creating an LongStream
        LongStream stream1 = LongStream.of(4L, 5L, 6L, 7L);

        // Using LongStream flatMap()
        LongStream stream2 = stream1.flatMap(num
                      -> LongStream.of(num * num * num));

        // Displaying the resulting LongStream
        stream2.forEach(System.out::println);
    }
}

Output :

64
125
216
343

Example 2 : Using LongStream flatMap() to get the count of set bits in binary representation of elements of LongStream.

// Java code for LongStream flatMap
// (LongFunction mapper) to get a stream
// consisting of the results of replacing
// each element of this stream with the
// contents of a mapped stream
import java.util.*;
import java.util.stream.LongStream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {
        // Creating an LongStream
        LongStream stream1 = LongStream.of(49L, 64L, 81L, 100L);

        // Using LongStream flatMap()
        LongStream stream2 = stream1.flatMap(num
                        -> LongStream.of(Long.bitCount(num)));

        // Displaying the resulting LongStream
        stream2.forEach(System.out::println);
    }
}

Output :

3
1
3
3