IntStream sum() in Java

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

int sum()

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

Example 1 :

Java

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

class GFG {

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

        // Using IntStream.sum() to find
        // sum of elements in IntStream
        int sumOfElements = stream.sum();

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

Output:

6

Example 2 :

Java

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

class GFG {

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

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

Output:

18