Java DoubleStream peek()方法及示例

DoubleStream peek() 是 java.util.stream.DoubleStream 中的一个方法。该函数返回一个由该流的元素组成的流，另外，当元素从产生的流中被消耗时，对每个元素执行所提供的操作。

DoubleStream peek()是一个 中间操作。 这些操作始终是懒惰的。中间操作是在一个流实例上调用的，在它们完成处理后，会给出一个流实例作为输出:

语法:

DoubleStream peek(DoubleConsumer action)

参数

DoubleStream : 一个原始双值元素的序列。
DoubleConsumer : 代表一个接受单一双值参数的操作，不返回结果。

返回值： 该函数返回一个并行的DoubleStream。

注意： 这个方法的存在主要是为了支持调试。

例子 1 : 执行求和操作，找出给定的DoubleStream中的元素之和。

// 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);
    }
}

输出:

2.2
3.3
4.5
6.7
sum is : 16.7

例2： 对给定的DoubleStream的元素进行计数操作。

// 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);
    }
}

输出:

2.2
3.3
4.5
6.7
count : 4

例3： 对给定的DoubleStream的元素进行平均操作。

// 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");
        }
    }
}

输出: