Java Stream mapToLong()用法及代碼示例

Stream mapToLong(ToLongFunction mapper)返回一個LongStream，其中包括將給定函數應用於此流的元素的結果。

流mapToLong(ToLongFunction mapper)是一個中間操作。這些操作總是很懶。在Stream實例上調用中間操作，並在完成處理後將中間實例作為輸出提供。

用法:

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.

範例1：mapToLong()函數，具有返回滿足給定函數的流的操作。

// 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); 
    } 
}

輸出：

The stream after applying the function is:
225

範例2：mapToLong()函數，以字符串長度返回set-bits。

// 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); 
    } 
}

輸出：

相關用法

注：本文由純淨天空篩選整理自Sahil_Bansall大神的英文原創作品 Stream mapToLong() in Java with examples。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。