LongStream peek() in Java with examples

Last Updated : 06 Dec, 2018

LongStream peek() is a method in java.util.stream.LongStream. The function returns a stream consisting of the elements of this stream, additionally performing the provided action on each element as elements are consumed from the resulting stream. Syntax :

LongStream peek(LongConsumer action)

Where, LongStream is a sequence of primitive
long-valued elements and the function returns 
a parallel LongStream and LongConsumer represents 
an operation that accepts a single long-valued argument.

Example 1 : Performing sum on a stream of given range.

Java

// Java code for LongStream peek()
// where the action performed is to get
// sum of all elements in given range
import java.util.*;
import java.util.stream.LongStream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {

        // Creating a stream of longs
        LongStream stream = LongStream.range(2L, 10L);

        // performing action sum on elements of
        // given range and storing the result in sum
        long sum = stream.peek(System.out::println).sum();

        // Displaying the result of action performed
        System.out.println("sum is : " + sum);
    }
}

Output:

2
3
4
5
6
7
8
9
sum is : 44

Example 2 : Performing count operation on a stream of given range.

Java

// Java code for LongStream peek()
// where the action performed is to get
// count of all elements in given range
import java.util.*;
import java.util.stream.LongStream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {

        // Creating a stream of longs
        LongStream stream = LongStream.range(2L, 10L);

        // performing action count on elements of
        // given range and storing the result in Count
        long Count = stream.peek(System.out::println).count();

        // Displaying the result of action performed
        System.out.println("count : " + Count);
    }
}

Output:

2
3
4
5
6
7
8
9
count : 8

Example 3 : Performing average operation on a stream of given range.

Java

// Java code for LongStream peek()
// where the action performed is to get
// average of all elements in given range
import java.util.*;
import java.util.OptionalDouble;
import java.util.stream.LongStream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {

        // Creating a stream of longs
        LongStream stream = LongStream.range(2L, 10L);

        // performing action average on elements of
        // given range and storing the result in avg
        OptionalDouble avg = stream.peek(System.out::println)
                                 .average();

        // If a value is present, isPresent()
        // will return true, else -1 is displayed.
        if (avg.isPresent()) {
            System.out.println("Average is : " + avg.getAsDouble());
        }
        else {
            System.out.println("-1");
        }
    }
}