Java 中的 Stream mapToLong()示例
哎哎哎:# t0]https://www . geeksforgeeks . org/stream-maptoolodlongfunction-mapper-Java/
Stream mapToLong(ToLongFunction mapper)返回一个 LongStream，该 LongStream 由给定函数应用于该流元素的结果组成。
流映射器(ToLongFunction mapper)是一个 中间操作 。这些操作总是偷懒。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。
语法:
LongStream mapToLong(ToLongFunction<**?** super **T**> 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 : mapToLong()函数，返回满足给定函数的流的操作。
// 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.*;
class GFG {
// Driver code
public static void main(String[] args)
{
System.out.println("The stream after applying "
+ "the function is : ");
// Creating a list of Strings
List<String> list = Arrays.asList("25", "225", "1000",
"20", "15");
// Using Stream mapToLong(ToLongFunction mapper)
// and displaying the corresponding LongStream
list.stream().mapToLong(num -> Long.parseLong(num))
.filter(num -> Math.sqrt(num) / 5 == 3 )
.forEach(System.out::println);
}
}
输出:
The stream after applying the function is :
225
示例 2 : 返回字符串长度中设定位数的 mapToLong()函数。
// 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.*;
class GFG {
// Driver code
public static void main(String[] args)
{
// Creating a list of Strings
List<String> list = Arrays.asList("Data Structures", "JAVA", "OOPS",
"GeeksforGeeks", "Algorithms");
// Using Stream mapToLong(ToLongFunction mapper)
// and displaying the corresponding LongStream
// which contains the number of one-bits in
// binary representation of String length
list.stream().mapToLong(str -> Long.bitCount(str.length()))
.forEach(System.out::println);
}
}
输出:
4
1
1
3
2
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