Java Stream mapToDouble()用法及代碼示例

Stream mapToDouble(ToDoubleFunction映射器)返回DoubleStream，該DoubleStream包含將給定函數應用於此 Stream 的元素的結果。

Stream mapToDouble(ToDoubleFunction映射器)是一個中間操作。這些操作總是很懶。在Stream實例上調用中間操作，並在完成處理後將中間實例作為輸出提供。

用法:

DoubleStream mapToDouble(ToDoubleFunction<? super T> mapper)

Where, A sequence of primitive double-valued
elements and T is the type of stream elements. 
mapper is a stateless function which is applied
to each element and the function returns the new stream.

範例1：mapToDouble()具有選擇滿足給定函數的元素的操作。

// Java code for Stream mapToDouble 
// (ToDoubleFunction mapper) to get a 
// DoubleStream by applying the given function 
// to the elements of this stream. 
import java.util.*; 
  
class GFG { 
  
    // Driver code 
    public static void main(String[] args) 
    { 
  
        // Creating a list of Strings 
        List<String> list = Arrays.asList("10", "6.548", "9.12", 
                                                    "11", "15"); 
  
        // Using Stream mapToDouble(ToDoubleFunction mapper) 
        // and displaying the corresponding DoubleStream 
        list.stream().mapToDouble(num -> Double.parseDouble(num)) 
                    .filter(num -> (num * num) * 2 == 450) 
                    .forEach(System.out::println); 
    } 
}

輸出：

15.0

範例2：mapToDouble()具有返回具有字符串長度平方的 Stream 的操作。

// Java code for Stream mapToDouble 
// (ToDoubleFunction mapper) to get a 
// DoubleStream by applying the given function 
// to the elements of this stream. 
import java.util.*; 
  
class GFG { 
  
    // Driver code 
    public static void main(String[] args) 
    { 
        // Creating a list of Strings 
        List<String> list = Arrays.asList("CSE", "JAVA", "gfg", 
                                                    "C++", "C"); 
  
        // Using Stream mapToDouble(ToDoubleFunction mapper) 
        // and displaying the corresponding DoubleStream 
        // which contains square of length of each element in 
        // given Stream 
        list.stream().mapToDouble(str -> str.length() * str.length()) 
                     .forEach(System.out::println); 
    } 
}

輸出：

9.0
16.0
9.0
9.0
1.0

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 Stream mapToDouble() in Java with examples。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。