Java ConcurrentLinkedQueue peek()方法

ConcurrentLinkedQueue 的 peek() 方法用于返回ConcurrentLinkedQueue的头部。它检索但不删除这个ConcurrentLinkedQueue的头部。如果ConcurrentLinkedQueue是空的，那么这个方法返回null。

语法

public E peek()

返回： 该方法返回该ConcurrentLinkedQueue的头部，但不删除它。

下面的程序说明了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]

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