Java IntStream mapToLong()

IntStream 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： IntStream 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，它们给出一个Stream实例作为输出。

语法

LongStream mapToLong(IntToLongFunction mapper)

参数

1. LongStream : 一个原始长值元素的序列。这是对Stream的长基元的特殊化。
2. mapper : 一个应用于每个元素的无状态函数。

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
// (IntToLongFunction mapper)
import java.util.*;
import java.util.stream.IntStream;
import java.util.stream.LongStream;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
        // Creating an IntStream
        IntStream stream = IntStream.of(2, 4, 6, 8, 10);
  
        // Using LongStream mapToLong(IntToLongFunction 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:

2
4
6
8
10

例2 :

// Java code for LongStream mapToLong
// (IntToLongFunction mapper)
import java.util.*;
import java.util.stream.IntStream;
import java.util.stream.LongStream;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
        // Creating an IntStream
        IntStream stream = IntStream.of(2, 4, 6, 8, 10);
  
        // Using LongStream mapToLong(IntToLongFunction 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 + Integer.MAX_VALUE);
  
        // Displaying the elements in stream1
        stream1.forEach(System.out::println);
    }
}

输出:

2147483649
2147483651
2147483653
2147483655
2147483657

例3 :

// Java code for LongStream mapToLong
// (IntToLongFunction mapper)
import java.util.*;
import java.util.stream.IntStream;
import java.util.stream.LongStream;
  
class GFG {
  
    // Driver code
    public static void main(String[] args)
    {
        // Creating an IntStream
        IntStream stream = IntStream.range(5, 10);
  
        // Using LongStream mapToLong(IntToLongFunction 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 - 20);
  
        // Displaying the elements in stream1
        stream1.forEach(System.out::println);
    }
}

输出:

-15
-14
-13
-12
-11