DoubleStream flatMap(DoubleFunction mapper) in Java

DoubleStream flatMap(DoubleFunction 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 :

DoubleStream flatMap(DoubleFunction<? extends DoubleStream> mapper)

Parameters :

1. DoubleStream : A sequence of primitive double-valued elements.
2. DoubleFunction : A function that accepts an double-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 : DoubleStream flatMap(DoubleFunction mapper) returns a stream by a mapped stream using mapping function.

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

// Java code for DoubleStream flatMap
// (DoubleFunction 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.DoubleStream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {
        // Creating an DoubleStream
        DoubleStream stream1 = DoubleStream.of(4.2, 5.3, 6.6, 7.0);

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

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

Output:

74.08800000000001
148.87699999999998
287.496
343.0

Example 2 :Using DoubleStream flatMap() to multiply every element of DoubleStream by 0.7

// Java code for DoubleStream flatMap
// (DoubleFunction 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.DoubleStream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {
        // Creating an DoubleStream
        DoubleStream stream1 = DoubleStream.of(5.2, 6.4, 8.1, 10.0);

        // Using DoubleStream flatMap()
        DoubleStream stream2 = stream1.flatMap(num
                     -> DoubleStream.of(num * 0.7));

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

Output:

3.6399999999999997
4.4799999999999995
5.669999999999999
7.0