Stream count() method in Java with examples

0 0 1 minute read

long count() returns the count of elements in the stream. This is a special case of a reduction (A reduction operation takes a sequence of input elements and combines them into a single summary result by repeated application of a combining operation). This is a terminal operation i.e, it may traverse the stream to produce a result or a side-effect. After the terminal operation is performed, the stream pipeline is considered consumed, and can no longer be used.

Syntax :

long count()

Note : The return value of count operation is the count of elements in the stream.

Example 1 : Counting number of elements in array.

// Java code for Stream.count()
// to count the elements in the stream.
import java.util.*;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
  
        // creating a list of Integers
        List<Integer> list = Arrays.asList(0, 2, 4, 6,
                                           8, 10, 12);
  
        // Using count() to count the number
        // of elements in the stream and
        // storing the result in a variable.
        long total = list.stream().count();
  
        // Displaying the number of elements
        System.out.println(total);
    }
}

Output :

Example 2 : Count number of distinct elements in a list.

// Java code for Stream.count()
// to count the number of distinct
// elements in the stream.
import java.util.*;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
  
        // creating a list of Strings
        List<String> list = Arrays.asList("GFG", "Geeks", "for", "Geeks",
                                          "Lazyroar", "GFG");
  
        // Using count() to count the number
        // of distinct elements in the stream and
        // storing the result in a variable.
        long total = list.stream().distinct().count();
  
        // Displaying the number of elements
        System.out.println(total);
    }
}