DoubleStream peek() in Java with examples

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DoubleStream peek() is a method in java.util.stream.DoubleStream. 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.

DoubleStream peek() is an 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 peek(DoubleConsumer action)

Parameters :

DoubleStream : A sequence of primitive double-valued elements.
DoubleConsumer : Represents an operation that accepts a single double-valued argument and returns no result.

Return Value : the function returns a parallel DoubleStream.

Note : This method exists mainly to support debugging.

Example 1 : Performing sum operation to find sum of elements of given DoubleStream.

// Java code for DoubleStream peek()
// where the action performed is to get
// sum of all elements.
import java.util.*;
import java.util.stream.DoubleStream;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
  
        // Creating a stream of doubles
        DoubleStream stream =
                DoubleStream.of(2.2, 3.3, 4.5, 6.7);
  
        // performing action sum on elements of
        // given range and storing the result in sum
        double sum = stream.peek(System.out::println).sum();
  
        // Displaying the result of action performed
        System.out.println("sum is : " + sum);
    }
}

Output:

2.2
3.3
4.5
6.7
sum is : 16.7

Example 2 : Performing count operation on elements of given DoubleStream.

// Java code for DoubleStream peek()
// where the action performed is to get
// count of all elements in given range
import java.util.*;
import java.util.stream.DoubleStream;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
  
        // Creating a stream of doubles
        DoubleStream stream =
                  DoubleStream.of(2.2, 3.3, 4.5, 6.7);
  
        // performing count operation on elements of
        // given DoubleStream 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:

2.2
3.3
4.5
6.7
count : 4

Example 3 : Performing average operation on elements of given DoubleStream.

// Java code for DoubleStream peek()
// where the action performed is to get
// average of all elements.
import java.util.*;
import java.util.OptionalDouble;
import java.util.stream.DoubleStream;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
  
        // Creating a stream of doubles
        DoubleStream stream =
                DoubleStream.of(2.2, 3.3, 4.5, 6.7);
        ;
  
        // performing action "average" on elements of
        // given DoubleStream 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");
        }
    }
}