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

这个 getFirst（） 方法 LinkedBlockingDeque 返回Deque容器中最前面的元素。如果LinkedBlockingDeque为空，则在函数调用时返回 非接触性异常 .

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语法：

public E getLast()

参数： 此方法不接受任何参数。

返回： 此方法返回此Deque容器的第一个元素或头。

例外情况： 该函数只引发一个异常，即：。， 非接触性异常 当deque是空的

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

项目1：

                     // Java Program Demonstrate getFirst()                   
                     // method of LinkedBlockingDeque                   
                             
                     import                               java.util.concurrent.LinkedBlockingDeque;                   
                     import                               java.util.*;                   
                             
                     public                               class                               GFG {                   
                                         public                               static                               void                               main(String[] args)                   
                                         throws                               IllegalStateException                   
                                         {                   
                             
                                         // create object of LinkedBlockingDeque                   
                                         LinkedBlockingDeque<Integer> LBD                   
                                         =                               new                               LinkedBlockingDeque<Integer>();                   
                             
                                         // Add numbers to front of LinkedBlockingDeque                   
                                         LBD.addFirst(                               7855642                               );                   
                                         LBD.addFirst(                               35658786                               );                   
                                         LBD.addFirst(                               5278367                               );                   
                                         LBD.addFirst(                               74381793                               );                   
                             
                                         // before removing print queue                   
                                         System.out.println(                               "Linked Blocking Deque: "                               + LBD);                   
                             
                                         // prints the first element                   
                                         System.out.println(                               "Linked Blocking Deque first element: "                               +                   
                                         LBD.getFirst());                   
                                         }                   
                     }                   

输出：

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

项目2：

                       // Java Program Demonstrate getFirst()                     
                       // method of LinkedBlockingDeque                     
                                
                       import                                  java.util.concurrent.LinkedBlockingDeque;                     
                       import                                  java.util.*;                     
                                
                       public                                  class                                  GFG {                     
                                             public                                  static                                  void                                  main(String[] args)                     
                                             throws                                  IllegalStateException                     
                                             {                     
                                
                                             // create object of LinkedBlockingDeque                     
                                             LinkedBlockingDeque<Integer> LBD                     
                                             =                                  new                                  LinkedBlockingDeque<Integer>();                     
                                
                                             // Add numbers to front of LinkedBlockingDeque                     
                                             LBD.addFirst(                                  7855642                                  );                     
                                             LBD.addFirst(                                  35658786                                  );                     
                                             LBD.addFirst(                                  5278367                                  );                     
                                             LBD.addFirst(                                  74381793                                  )                     
                                
                                             LBD.clear();                     
                                
                                             // Since the container is empty it will throw exception                     
                                             System.out.println(                                  "Linked Blocking Deque first element: "                                  +                     
                                             LBD.getFirst());                     
                                             }                     
                       }                     

输出：

Exception in thread "main" java.util.NoSuchElementException
    at java.util.concurrent.LinkedBlockingDeque.getFirst(LinkedBlockingDeque.java:553)
    at GFG.main(GFG.java:28)

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

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