带有示例的Java流 count() 方法

在Java 8 中， Collectors类的counting( )方法返回了预定义的counting() 方法来计算Stream 中元素的数量。

Syntax :
public static Collector counting() Where, output is a Collector, acting on a Stream of elements of type T, with its finisher returning the ‘collected’ value of type Long. It is a terminal operation which returns the total count of elements in the stream which reach the collect() method after undergoing various pipelined stream operations such as filtering.

示例 1：计算整数流中的元素。

// Java code to count number of elements 
// in stream
import java.util.stream.Stream;
import java.util.stream.Collectors;
class counting {
    public static void main(String[] args)
    {
        // creating stream of integers
        Stream i = Stream.of(1, 2, 3, 4, 5, 6);
  
        // counting number of integer in stream
        long count_int = i.collect(Collectors.counting());
  
        System.out.println(count_int);
    }
}

输出：

6

示例 2：统计 String 流中的元素。

// JAVA code to count number of elements in stream
import java.util.stream.Stream;
import java.util.stream.Collectors;
  
class counting {
    public static void main(String[] args)
    {
        // creating stream of strings
        Stream s = Stream.of("Akash","Harsh",
                        "Shubham","Nishant","Pratik");
  
        // counting number of strings in stream
        long count_string =  s.collect(Collectors.counting());
  
        System.out.println(count_string);
    }
}

输出：

5