Java DoubleStream reduce(DoubleBinaryOperator op)用法及代码示例

DoubleStream reduce(DoubleBinaryOperator op)使用关联的累加函数对此流的元素进行归约，并返回描述缩减后的值的OptionalDouble(如果有)。

归约运算或折叠运算采用一系列输入元素，并将它们组合成单个汇总结果，例如查找一组数字的总和或最大值。如果满足以下条件，则运算符或函数op是关联的：

(a op b) op c == a op (b op c)

这是终端操作，即可能会遍历流以产生结果或副作用。执行终端操作后，流管线被视为已消耗，无法再使用。

用法:

OptionalDouble reduce(DoubleBinaryOperator op)

参数：

OptionalDouble:可能包含或可能不包含long值的容器对象。如果存在值，则isPresent()将返回true，而getAsDouble()将返回该值。
DoubleBinaryOperator:对两个双值操作数进行运算并产生双值结果。
op:用于组合两个值的关联无状态函数。

返回值：描述减小的值的OptionalDouble(如果有)。

范例1：

// Java code for DoubleStream reduce 
// (DoubleBinaryOperator op) 
import java.util.OptionalDouble; 
import java.util.stream.DoubleStream; 
  
class GFG { 
  
    // Driver code 
    public static void main(String[] args) 
    { 
        // Creating a DoubleStream 
        DoubleStream stream = DoubleStream.of(1.2, 2.3, 3.4, 4.5); 
  
        // Using OptionalDouble (a container object which 
        // may or may not contain a non-null value) 
        // Using DoubleStream reduce(DoubleBinaryOperator op) 
        OptionalDouble answer = stream.reduce(Double::sum); 
  
        // if the stream is empty, an empty 
        // OptionalDouble is returned. 
        if (answer.isPresent()) { 
            System.out.println(answer.getAsDouble()); 
        } 
        else { 
            System.out.println("Stream is empty"); 
        } 
    } 
}

输出：

11.4

范例2：

// Java code for DoubleStream reduce 
// (DoubleBinaryOperator op) 
import java.util.OptionalDouble; 
import java.util.stream.DoubleStream; 
  
class GFG { 
  
    // Driver code 
    public static void main(String[] args) 
    { 
        // Creating a DoubleStream 
        DoubleStream stream = DoubleStream.of(1.2, 2.3, 3.4, 4.5); 
  
        // Using OptionalDouble (a container object which 
        // may or may not contain a non-null value) 
        // Using DoubleStream reduce(DoubleBinaryOperator op) 
        OptionalDouble answer = stream.reduce((a, b) 
                                  -> (a * b) * (a * b)); 
  
        // if the stream is empty, an empty 
        // OptionalDouble is returned. 
        if (answer.isPresent()) { 
            System.out.println(answer.getAsDouble()); 
        } 
        else { 
            System.out.println("Stream is empty"); 
        } 
    } 
}

输出：

9111992.471343633

相关用法

注：本文由纯净天空筛选整理自Sahil_Bansall大神的英文原创作品 DoubleStream reduce(DoubleBinaryOperator op) in Java。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。