Java DoubleStream reduce(DoubleBinaryOperator op)用法及代碼示例

DoubleStream reduce(DoubleBinaryOperator op)使用關聯的累加函數對此流的元素進行歸約，並返回描述縮減後的值的OptionalDouble(如果有)。

歸約運算或折疊運算采用一係列輸入元素，並將它們組合成單個匯總結果，例如查找一組數字的總和或最大值。如果滿足以下條件，則運算符或函數op是關聯的：

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

這是終端操作，即可能會遍曆流以產生結果或副作用。執行終端操作後，流管線被視為已消耗，無法再使用。

用法:

OptionalDouble reduce(DoubleBinaryOperator op)

參數：

OptionalDouble:可能包含或可能不包含long值的容器對象。如果存在值，則isPresent()將返回true，而getAsDouble()將返回該值。
DoubleBinaryOperator:對兩個雙值操作數進行運算並產生雙值結果。
op:用於組合兩個值的關聯無狀態函數。

返回值：描述減小的值的OptionalDouble(如果有)。

範例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"); 
        } 
    } 
}

輸出：

11.4

範例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"); 
        } 
    } 
}

輸出：

9111992.471343633

相關用法

注：本文由純淨天空篩選整理自Sahil_Bansall大神的英文原創作品 DoubleStream reduce(DoubleBinaryOperator op) in Java。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。