Java Stream mapToDouble()用法及代码示例

Stream mapToDouble(ToDoubleFunction映射器)返回DoubleStream，该DoubleStream包含将给定函数应用于此 Stream 的元素的结果。

Stream mapToDouble(ToDoubleFunction映射器)是一个中间操作。这些操作总是很懒。在Stream实例上调用中间操作，并在完成处理后将中间实例作为输出提供。

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.

范例1：mapToDouble()具有选择满足给定函数的元素的操作。

// 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); 
    } 
}

输出：

15.0

范例2：mapToDouble()具有返回具有字符串长度平方的 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); 
    } 
}

输出：

9.0
16.0
9.0
9.0
1.0

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 Stream mapToDouble() in Java with examples。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。