Java 中的 Stream flatMapToLong()示例
原文:https://www . geesforgeks . org/stream-flatmaptolong-Java-examples/
Stream flatMapToLong(函数映射器)将给定的映射器函数应用于流的每个元素，并返回一个 LongStream。流平面映射器(功能映射器)是 中间操作 。中间操作在流实例上被调用，在它们完成处理后，它们给出一个流实例作为输出。
注意:每个映射的流在其内容被放入该流后被关闭。如果映射的流为空，则改为使用空流。 语法:
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.
例 1 : flatMapToLong()的解析字符串操作为 Long。
// 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:
1
2
3
4
5
例 2 : flatMapToLong()带有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:
5
3
13
3
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:一个 Javanumberformateexception通常发生在你试图把一个字符串转换成一个数值的时候，比如 int、float、double、long 等等。
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