Java LongStream mapToDouble()用法及代码示例

LongStream mapToDouble()返回DoubleStream，该DoubleStream包含将给定函数应用于此流的元素的结果。

注意：LongStream mapToDouble()是中间操作。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(LongToDoubleFunction mapper)

参数：

DoubleStream : 一系列原始双值元素。这是Stream的双重原始专业化。
mapper : 适用于每个元素的无状态函数。

返回值：该函数返回一个DoubleStream，其中包括将给定函数应用于此流的元素的结果。

示例1:

// Java code for DoubleStream mapToDouble 
// (LongToDoubleFunction mapper) 
import java.util.*; 
import java.util.stream.LongStream; 
import java.util.stream.DoubleStream; 
  
class GFG { 
  
    // Driver code 
    public static void main(String[] args) 
    { 
        // Creating an LongStream 
        LongStream stream = LongStream.of(2L, 4L, 6L, 8L, 10L); 
  
        // Using DoubleStream mapToLong(LongToDoubleFunction mapper) 
        // to return a DoubleStream consisting of the 
        // results of applying the given function to 
        // the elements of this stream. 
        DoubleStream stream1 = stream.mapToDouble(num -> (double)num); 
  
        // Displaying the elements in stream1 
        stream1.forEach(System.out::println); 
    } 
}

输出：

2.0
4.0
6.0
8.0
10.0

示例2:

// Java code for DoubleStream mapToDouble 
// (LongToDoubleFunction mapper) 
import java.util.*; 
import java.util.stream.LongStream; 
import java.util.stream.DoubleStream; 
  
class GFG { 
  
    // Driver code 
    public static void main(String[] args) 
    { 
        // Creating an LongStream 
        LongStream stream = LongStream.range(5L, 10L); 
  
        // Using DoubleStream mapToLong(LongToDoubleFunction mapper) 
        // to return a DoubleStream consisting of the 
        // results of applying the given function to 
        // the elements of this stream. 
        DoubleStream stream1 = stream.mapToDouble(num -> (double)num / 5); 
  
        // Displaying the elements in stream1 
        stream1.forEach(System.out::println); 
    } 
}

输出：

1.0
1.2
1.4
1.6
1.8

示例3:

// Java code for DoubleStream mapToDouble 
// (LongToDoubleFunction mapper) 
import java.util.*; 
import java.util.stream.LongStream; 
import java.util.stream.DoubleStream; 
  
class GFG { 
  
    // Driver code 
    public static void main(String[] args) 
    { 
        // Creating an LongStream 
        LongStream stream = LongStream.range(5L, 10L); 
  
        // Using DoubleStream mapToLong(LongToDoubleFunction mapper) 
        // to return a DoubleStream consisting of the 
        // results of applying the given function to 
        // the elements of this stream. 
        DoubleStream stream1 = stream.mapToDouble(Math::cos); 
  
        // Displaying the elements in stream1 
        stream1.forEach(System.out::println); 
    } 
}

输出：

0.28366218546322625
0.9601702866503661
0.7539022543433046
-0.14550003380861354
-0.9111302618846769

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注：本文由纯净天空筛选整理自Sahil_Bansall大神的英文原创作品 LongStream mapToDouble() 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。