Java中的ConcurrentLinkedQueue peek（）方法-yiteyi-C++库

这个 peek（） 方法 ConcurrentLinkedQueue 用于返回ConcurrentLinkedQueue的头。它检索但不删除此ConcurrentLinkedQueue的头。如果ConcurrentLinkedQueue为空，则此方法返回null。

null

语法：

public E peek()

返回： 此方法返回头不删除此ConcurrentLinkedQueue。

下面的程序演示了ConcurrentLinkedQueue的peek（）方法：

例1：

                     // Java Program Demonstrate peek()                   
                     // method of ConcurrentLinkedQueue                   
                             
                     import                               java.util.concurrent.*;                   
                             
                     public                               class                               GFG {                   
                                         public                               static                               void                               main(String[] args)                   
                                         {                   
                             
                                         // create an ConcurrentLinkedQueue                   
                                         ConcurrentLinkedQueue<Integer>                   
                                         queue =                               new                               ConcurrentLinkedQueue<Integer>();                   
                             
                                         // Add Numbers to queue                   
                                         queue.add(                               4353                               );                   
                                         queue.add(                               7824                               );                   
                                         queue.add(                               78249                               );                   
                                         queue.add(                               8724                               );                   
                             
                                         // Displaying the existing ConcurrentLinkedQueue                   
                                         System.out.println(                               "ConcurrentLinkedQueue: "                               + queue);                   
                             
                                         // find peek                   
                                         int                               response1 = queue.peek();                   
                             
                                         // print after applying peek method                   
                                         System.out.println(                               "Head: "                               + response1);                   
                             
                                         // Verifying that the head is not removed                   
                                         System.out.println(                               "ConcurrentLinkedQueue after peek: "                               + queue);                   
                                         }                   
                     }                   

输出：

ConcurrentLinkedQueue: [4353, 7824, 78249, 8724]
Head: 4353
ConcurrentLinkedQueue after peek: [4353, 7824, 78249, 8724]

例2：

                     // Java Program Demonstrate peek()                   
                     // method of ConcurrentLinkedQueue                   
                             
                     import                               java.util.concurrent.*;                   
                             
                     public                               class                               GFG {                   
                                         public                               static                               void                               main(String[] args)                   
                                         {                   
                             
                                         // create an ConcurrentLinkedQueue                   
                                         ConcurrentLinkedQueue<String>                   
                                         queue =                               new                               ConcurrentLinkedQueue<String>();                   
                             
                                         // Add String to queue                   
                                         queue.add(                               "Aman"                               );                   
                                         queue.add(                               "Amar"                               );                   
                                         queue.add(                               "Sanjeet"                               );                   
                                         queue.add(                               "Rabi"                               );                   
                             
                                         // Displaying the existing ConcurrentLinkedQueue                   
                                         System.out.println(                               "ConcurrentLinkedQueue: "                               + queue);                   
                             
                                         // find peek of queue                   
                                         String response1 = queue.peek();                   
                             
                                         // print after applying peek method                   
                                         System.out.println(                               "Head: "                               + response1);                   
                             
                                         // Verifying that the head is not removed                   
                                         System.out.println(                               "ConcurrentLinkedQueue after peek: "                               + queue);                   
                             
                                         // remove some elements                   
                                         queue.poll();                   
                                         queue.poll();                   
                             
                                         // Displaying the existing ConcurrentLinkedQueue                   
                                         System.out.println(                               "Updated ConcurrentLinkedQueue: "                               + queue);                   
                             
                                         // find peek of queue                   
                                         String response2 = queue.peek();                   
                             
                                         // print after applying peek method                   
                                         System.out.println(                               "Head: "                               + response1);                   
                             
                                         // Verifying that the head is not removed                   
                                         System.out.println(                               "ConcurrentLinkedQueue after peek: "                               + queue);                   
                                         }                   
                     }                   

输出：

ConcurrentLinkedQueue: [Aman, Amar, Sanjeet, Rabi]

Head: Aman

ConcurrentLinkedQueue after peek: [Aman, Amar, Sanjeet, Rabi]

Updated ConcurrentLinkedQueue: [Sanjeet, Rabi]

Head: Aman

ConcurrentLinkedQueue after peek: [Sanjeet, Rabi]

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

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