Java Stream flatMapToLong()用法及代码示例

Stream flatMapToLong(Function mapper)将给定的mapper函数应用于流的每个元素，并返回LongStream。 Stream flatMapToLong(Function mapper)是一个中间操作。在Stream实例上调用中间操作，并在完成处理后将中间实例作为输出提供。

注意：将每个映射流的内容放入该流后，将其关闭。如果映射的流为null，则使用空流。
用法:

LongStream flatMapToLong(Function<? super T, ? extends LongStream> mapper)

Where, LongStream is a sequence of primitive
long-valued elements and T is the type 
of stream elements. mapper is a stateless function 
which is applied to each element and the function
returns the new stream.

示例1:flatMapToLong()具有将字符串解析为long的操作。

// Java code for Stream flatMapToLong 
// (Function mapper) to get an LongStream 
// consisting of the results of replacing 
// each element of this stream with the 
// contents of a mapped stream. 
import java.util.*; 
import java.util.stream.LongStream; 
  
class GFG { 
  
    // Driver code 
    public static void main(String[] args) 
    { 
  
        // Creating a list of Strings 
        List<String> list = Arrays.asList("1", "2", "3", 
                                          "4", "5"); 
  
        // Using Stream flatMapToLong(Function mapper) 
        list.stream().flatMapToLong(num ->  
                     LongStream.of(Long.parseLong(num))). 
                            forEach(System.out::println); 
    } 
}

输出：

示例2:flatMapToLong()具有按字符串长度映射字符串的操作。

// Java code for Stream flatMapToLong 
// (Function mapper) to get an LongStream 
// consisting of the results of replacing 
// each element of this stream with the 
// contents of a mapped stream. 
import java.util.*; 
import java.util.stream.LongStream; 
  
class GFG { 
  
    // Driver code 
    public static void main(String[] args) 
    { 
  
        // Creating a List of Strings 
        List<String> list = Arrays.asList("Geeks", "GFG", 
                                 "GeeksforGeeks", "gfg"); 
  
        // Using Stream flatMapToLong(Function mapper) 
        // to get length of all strings present in list 
        list.stream().flatMapToLong(str ->  
                        LongStream.of(str.length())). 
                        forEach(System.out::println); 
    } 
}

输出：

示例3:flatMapToLong()函数，具有返回流的操作。

// Java code for Stream mapToLong 
// (ToLongFunction mapper) to get a 
// LongStream by applying the given function 
// to the elements of this stream. 
import java.util.*; 
import java.util.stream.LongStream; 
  
class GFG { 
  
    // Driver code 
    public static void main(String[] args) 
    { 
        // Creating a list of Strings 
        List<String> list = Arrays.asList("5.36","27.9", 
                                         "3","4.2","5"); 
  
        // Using Stream mapToLong(ToLongFunction mapper) 
        // and displaying the corresponding LongStream 
        list.stream().flatMapToLong(n 
                     -> LongStream.of(Long.parseLong(n)) ) 
                     .forEach(System.out::println); 
    } 
}

输出：

Exception in thread "main" java.lang.NumberFormatException: For input string: "5.36"

注意：当您尝试执行将String转换为数值(例如int，float，double，long等)时，通常会发生Java NumberFormatException。

相关用法

注：本文由纯净天空筛选整理自Sahil_Bansall大神的英文原创作品 Stream flatMapToLong() in Java with examples。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。