Java中的LongStream mapToDouble（）-yiteyi-C++库

LongStream mapToDouble（） 返回一个DoubleStream，其中包含将给定函数应用于该流元素的结果。

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注： LongStream mapToDouble（）是一个 中间操作。 这些操作总是懒惰的。在流实例上调用中间操作，完成处理后，它们将流实例作为输出。 语法：

DoubleStream mapToDouble(LongToDoubleFunction mapper)

参数：

双流： 一个原始的双值元素序列。这是人类的双重本原特化流动 .
制图员： 应用于每个元素的无状态函数。

返回值： 该函数返回一个DoubleStream，其中包含将给定函数应用于该流元素的结果。

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

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

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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