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:

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
-4
6
-2
0

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: