Java ConcurrentSkipListSet pollFirst()用法及代碼示例

java.util.concurrent.ConcurrentSkipListSet的pollFirst()方法是Java中的一個內置函數，該函數返回檢索並刪除第一個(最低)元素，如果此集為空，則返回null。

用法:

public E pollFirst()

返回值：該函數返回以檢索並刪除第一個(最低)元素，如果此集合為空，則返回null。

以下示例程序旨在說明ConcurrentSkipListSet.pollFirst()方法：

示例1:

// Java program to demonstrate pollFirst() 
// method of ConcurrentSkipListSet 
  
import java.util.concurrent.*; 
  
class ConcurrentSkipListSetpollFirstExample1 { 
    public static void main(String[] args) 
    { 
        // Creating a set object 
        ConcurrentSkipListSet<Integer>  
Lset = new ConcurrentSkipListSet<Integer>(); 
  
        // Adding elements to this set 
        for (int i = 10; i <= 50; i += 10) 
            Lset.add(i); 
  
        // Printing the content of the set 
        System.out.println("Contents of the set: " + Lset); 
  
        // Retrieving and removing first element of the set 
        System.out.println("The first element of the set: " 
+ Lset.pollFirst()); 
  
        // Printing the content of the set after pollFirst() 
        System.out.println("Contents of the set after pollFirst: " 
+ Lset); 
    } 
}

輸出：

Contents of the set: [10, 20, 30, 40, 50]
The first element of the set: 10
Contents of the set after pollFirst: [20, 30, 40, 50]

示例2:

// Java program to demonstrate pollFirst() 
// method of ConcurrentSkipListSet 
  
import java.util.concurrent.*; 
  
class ConcurrentSkipListSetpollFirstExample2 { 
    public static void main(String[] args) 
    { 
        // Creating a set object 
        ConcurrentSkipListSet<Integer>  
Lset = new ConcurrentSkipListSet<Integer>(); 
  
        // Printing the content of the set 
        System.out.println("Contents of the set: " + Lset); 
  
        // Retrieving and removing first element of the set 
        System.out.println("The first element of the set: " 
+ Lset.pollFirst()); 
    } 
}

輸出：

Contents of the set: []
The first element of the set: null

參考：
https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentSkipListSet.html#pollFirst–

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注：本文由純淨天空篩選整理自rupesh_rao大神的英文原創作品 ConcurrentSkipListSet pollFirst() method in Java。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。