LongStream sum() in Java

LongStream sum() returns the sum of elements in this stream. This is a special case of a reduction. LongStream 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 :

long sum()

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

Example 1 :

Java

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

class GFG {

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

        // Using LongStream.sum() to find
        // sum of elements in LongStream
        long sumOfElements = stream.sum();

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

Output:

6

Example 2 :

Java

// Java code for LongStream.sum() to
// find the sum of elements
// divisible by 3 in given range
import java.util.*;
import java.util.stream.LongStream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {
        // Using LongStream.sum() to find
        // sum of elements divisible by 3
        // in given range
        long sumOfElements = LongStream.range(2L, 10L)
                                 .filter(num -> num % 3 == 0)
                                 .sum();

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

Output:

18