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

这个 pollFirst（） 方法 LinkedBlockingDeque 返回Deque容器中的front元素，并将其删除。它回来了 无效的 如果容器是空的。

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语法：

public E pollFirst()

参数： 此方法不接受任何参数。

返回： 此方法返回 前元素 如果容器不是空的，则在Deque容器中删除该元素。它回来了 无效的 如果容器是空的。

下面的程序演示了LinkedBlockingDeque的pollFirst（）方法：

项目1：

                     // Java Program Demonstrate pollFirst()                   
                     // method of LinkedBlockingDeque                   
                             
                     import                               java.util.concurrent.LinkedBlockingDeque;                   
                     import                               java.util.*;                   
                             
                     public                               class                               GFG {                   
                                         public                               static                               void                               main(String[] args)                   
                             
                                         {                   
                             
                                         // create object of LinkedBlockingDeque                   
                                         LinkedBlockingDeque<Integer> LBD                   
                                         =                               new                               LinkedBlockingDeque<Integer>();                   
                             
                                         // Add numbers to end of LinkedBlockingDeque                   
                                         LBD.addFirst(                               7855642                               );                   
                                         LBD.addFirst(                               35658786                               );                   
                                         LBD.addFirst(                               5278367                               );                   
                                         LBD.addFirst(                               74381793                               );                   
                             
                                         // Print the queue                   
                                         System.out.println(                               "Linked Blocking Deque: "                               + LBD);                   
                             
                                         // prints and deletes                   
                                         System.out.println(                               "Front element in Deque: "                               + LBD.pollFirst());                   
                             
                                         // Deque after deletion of front element                   
                                         System.out.println(                               "Linked Blocking Deque: "                               + LBD);                   
                                         }                   
                     }                   

输出：

Linked Blocking Deque: [74381793, 5278367, 35658786, 7855642]
Front element in Deque: 74381793
Linked Blocking Deque: [5278367, 35658786, 7855642]

项目2：

                     // Java Program Demonstrate pollFirst()                   
                     // method of LinkedBlockingDeque                   
                     // when Deque is empty                   
                             
                     import                               java.util.concurrent.LinkedBlockingDeque;                   
                     import                               java.util.*;                   
                             
                     public                               class                               GFG {                   
                                         public                               static                               void                               main(String[] args)                   
                             
                                         {                   
                             
                                         // create object of LinkedBlockingDeque                   
                                         LinkedBlockingDeque<Integer> LBD                   
                                         =                               new                               LinkedBlockingDeque<Integer>();                   
                             
                                         // Add numbers to end of LinkedBlockingDeque                   
                                         LBD.add(                               7855642                               );                   
                                         LBD.add(                               35658786                               );                   
                                         LBD.add(                               5278367                               );                   
                                         LBD.add(                               74381793                               );                   
                             
                                         // Print the queue                   
                                         System.out.println(                               "Linked Blocking Deque: "                               + LBD);                   
                             
                                         // empty deque                   
                                         LBD.clear();                   
                             
                                         System.out.println(                               "Front element in Deque: "                               + LBD.pollFirst());                   
                                         }                   
                     }                   

输出：

Linked Blocking Deque: [7855642, 35658786, 5278367, 74381793]
Front element in Deque: null

参考： https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/LinkedBlockingDeque.html#pollFirst()

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