LongStream mapToDouble() in Java

LongStream mapToDouble() returns a DoubleStream consisting of the results of applying the given function to the elements of this stream.

Note : LongStream mapToDouble() is a 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.
Syntax :

DoubleStream mapToDouble(LongToDoubleFunction mapper)

Parameters :

1. DoubleStream : A sequence of primitive double-valued elements. This is the double primitive specialization of Stream.
2. mapper : A stateless function to apply to each element.

Return Value : The function returns a DoubleStream consisting of the results of applying the given function to the elements of this stream.

Example 1 :

// Java code for DoubleStream mapToDouble
// (LongToDoubleFunction mapper)
import java.util.*;
import java.util.stream.LongStream;
import java.util.stream.DoubleStream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {
        // Creating an LongStream
        LongStream stream = LongStream.of(2L, 4L, 6L, 8L, 10L);

        // Using DoubleStream mapToLong(LongToDoubleFunction mapper)
        // to return a DoubleStream consisting of the
        // results of applying the given function to
        // the elements of this stream.
        DoubleStream stream1 = stream.mapToDouble(num -> (double)num);

        // Displaying the elements in stream1
        stream1.forEach(System.out::println);
    }
}

Output :

2.0
4.0
6.0
8.0
10.0

Example 2 :

// Java code for DoubleStream mapToDouble
// (LongToDoubleFunction mapper)
import java.util.*;
import java.util.stream.LongStream;
import java.util.stream.DoubleStream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {
        // Creating an LongStream
        LongStream stream = LongStream.range(5L, 10L);

        // Using DoubleStream mapToLong(LongToDoubleFunction mapper)
        // to return a DoubleStream consisting of the
        // results of applying the given function to
        // the elements of this stream.
        DoubleStream stream1 = stream.mapToDouble(num -> (double)num / 5);

        // Displaying the elements in stream1
        stream1.forEach(System.out::println);
    }
}

Output :

1.0
1.2
1.4
1.6
1.8

Example 3 :

// Java code for DoubleStream mapToDouble
// (LongToDoubleFunction mapper)
import java.util.*;
import java.util.stream.LongStream;
import java.util.stream.DoubleStream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {
        // Creating an LongStream
        LongStream stream = LongStream.range(5L, 10L);

        // Using DoubleStream mapToLong(LongToDoubleFunction mapper)
        // to return a DoubleStream consisting of the
        // results of applying the given function to
        // the elements of this stream.
        DoubleStream stream1 = stream.mapToDouble(Math::cos);

        // Displaying the elements in stream1
        stream1.forEach(System.out::println);
    }
}

Output :

0.28366218546322625
0.9601702866503661
0.7539022543433046
-0.14550003380861354
-0.9111302618846769