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LongStream flatMap(LongFunction mapper) in Java

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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


Last Updated : 06 Dec, 2018
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