Java中的ConcurrentSkipListSet pollFirst（）方法-yiteyi-C++库

这个 pollFirst（） 方法 JAVAutil。同时发生的ConcurrentSkipListSet 是Java中的一个内置函数，返回并删除第一个（最低）元素，如果此集合为空，则返回null。

null

语法：

public E pollFirst()

返回值： 函数返回并移除第一个（最低）元素，如果该集合为空，则返回null。

下面的程序演示了ConcurrentSkipListSet。pollFirst（）方法：

项目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);                   
                                         }                   
                     }                   

输出：

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]

项目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());                   
                                         }                   
                     }                   

输出：

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

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

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