Java DoubleStream mapToLong()

DoubleStream mapToLong() 返回一个LongStream，由对这个流的元素应用给定函数的结果组成。

注意： DoubleStream mapToLong()是一个 中间操作。 这些操作总是懒惰的。中间操作是在一个Stream实例上调用的，在它们完成处理后，会给出一个Stream实例作为输出:

语法

LongStream mapToLong(DoubleToLongFunction mapper)

参数

DoubleStream : 一个原始双值元素的序列。这是对Stream的双重原始特化。mapper : 一个无状态函数，应用于每个元素。

返回值： 该函数返回一个LongStream，由对该流的元素应用给定函数的结果组成。

例子 1 :

// Java code for LongStream mapToLong// (DoubleToLongFunction 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 a DoubleStream        DoubleStream stream = DoubleStream.of(3.3, 6.5, 16.4,                                              8.7, 10.4);          // Using LongStream mapToLong(DoubleToLongFunction mapper)        // to return a LongStream consisting of the        // results of applying the given function to        // the elements of this stream.        LongStream stream1 = stream.mapToLong(num -> (long)num);          // Displaying the elements in stream1        stream1.forEach(System.out::println);    }}

输出:

3616810

例2 :

// Java code for LongStream mapToLong// (DoubleToLongFunction 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 a DoubleStream        DoubleStream stream = DoubleStream.of(3.3, 6.5, 16.4,                                              8.7, 10.4);          // Using LongStream mapToLong(DoubleToLongFunction mapper)        // to return a LongStream consisting of the        // results of applying the given function to        // the elements of this stream.        LongStream stream1 = stream.mapToLong(num -> (long)num - 10);          // Displaying the elements in stream1        stream1.forEach(System.out::println);    }}

输出:

-7-46-20

例3 :

// Java code for LongStream mapToLong// (DoubleToLongFunction 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 a DoubleStream        DoubleStream stream = DoubleStream.of(3.3, 6.5, 16.4,                                              8.7, 10.4);          // Using LongStream mapToLong(DoubleToLongFunction mapper)        // to return a LongStream consisting of the        // results of applying the given function to        // the elements of this stream.        LongStream stream1 = stream.mapToLong(num -> (long)(2 * num * num));          // Displaying the elements in stream1        stream1.forEach(System.out::println);    }}

输出:

2184537151216