Java中的 LongStream mapToInt() 和示例

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

注意： LongStream mapToInt() 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 mapToInt(LongToIntFunction 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 IntStream，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 mapToInt
// (LongToIntFunction 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 a LongStream
        LongStream stream = LongStream.of(2L, 4L, 6L, 8L, 10L);
          
        // Using LongStream mapToInt(LongToIntFunction mapper)
        // to return an IntStream consisting of the
        // results of applying the given function to 
        // the elements of this stream.
        IntStream stream1 = stream.mapToInt(num -> (int) 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 mapToInt
// (LongToIntFunction 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 a LongStream
        LongStream stream = LongStream.of(1L, 2L, 3L, 4L, 5L);
          
        // Using LongStream mapToInt(LongToIntFunction mapper)
        // to return an IntStream consisting of the
        // results of applying the given function to 
        // the elements of this stream.
        IntStream stream1 = stream.mapToInt(num ->
                                   (int) num + Integer.MAX_VALUE); 
  
        // Displaying the elements in stream1
        stream1.forEach(System.out::println);
    }
}

输出 ：

-2147483648
-2147483647
-2147483646
-2147483645
-2147483644

示例 3：

// Java code for LongStream mapToInt
// (LongToIntFunction 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 a LongStream
        LongStream stream = LongStream.range(2L, 7L);
          
        // Using LongStream mapToInt(LongToIntFunction mapper)
        // to return an IntStream consisting of the
        // results of applying the given function to 
        // the elements of this stream.
        IntStream stream1 = stream.mapToInt(num ->
                                    (int) num - 2); 
  
        // Displaying the elements in stream1
        stream1.forEach(System.out::println);
    }
}

输出 ：

0
1
2
3
4