Java中的 IntStream mapToLong()

IntStream mapToLong()返回一个 LongStream，其中包含将给定函数应用于此流的元素的结果。

注意： IntStream mapToLong() 是一个中间操作。这些操作总是懒惰的。在 Stream 实例上调用中间操作，在它们完成处理后，它们给出一个 Stream 实例作为输出。
句法 ：

LongStream mapToLong(IntToLongFunction mapper)

参数 ：

1. LongStream ：原始长值元素的序列。这是 Stream 的长期原始特化。
2. mapper ：应用于每个元素的无状态函数。

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

示例 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

示例 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

示例 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