DoubleStream sum() in Java

DoubleStream sum() returns the sum of elements in this stream. This is a special case of a reduction. DoubleStream sum() is a terminal operation i.e, it may traverse the stream to produce a result or a side-effect.

Note : A reduction operation (also called a fold) takes a sequence of input elements and combines them into a single summary result by repeated application of a combining operation, such as finding the sum or maximum of a set of numbers.

Syntax :

double sum()

Return Value : The function returns the sum of elements in this stream.

Note :

1. If any stream element is a NaN or the sum is at any point a NaN then the sum will be NaN.
2. Elements sorted by increasing absolute magnitude tend to yield more accurate result.

Example 1 :

// Java code for DoubleStream.sum() to
// find the sum of elements in DoubleStream
import java.util.*;
import java.util.stream.DoubleStream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {
        // Creating an DoubleStream
        DoubleStream stream = DoubleStream.of(2.2, 4.3, 6.4,
                                              -2.5, -4.6);

        // Using DoubleStream.sum() to find
        // sum of elements in DoubleStream
        double sumOfElements = stream.sum();

        // Displaying the calculated sum
        System.out.println(sumOfElements);
    }
}

Output:

5.800000000000001

Example 2 :

// Java code for DoubleStream.sum() to
// find the sum of elements
// greater than 2.5
import java.util.*;
import java.util.stream.DoubleStream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {
        // Creating an DoubleStream
        // Using DoubleStream.sum() to find
        // sum of elements greater than 2.5
        double sumOfElements = DoubleStream.of(2.2, 4.2, 6.4,
                                               -2.5, -4.5)
                                   .filter(num -> num > 2.5)
                                   .sum();

        // Displaying the calculated sum
        System.out.println(sumOfElements);
    }
}

Output:

10.600000000000001