The peek() method of ConcurrentLinkedQueue is used to return the head of the ConcurrentLinkedQueue. It retrieves but does not remove, the head of this ConcurrentLinkedQueue. If the ConcurrentLinkedQueue is empty then this method returns null.
Syntax:
public E peek()
Returns: This method returns the head of this ConcurrentLinkedQueue without removing it.
Below programs illustrate peek() method of ConcurrentLinkedQueue:
Example 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);    }} |
Output:
ConcurrentLinkedQueue: [4353, 7824, 78249, 8724] Head: 4353 ConcurrentLinkedQueue after peek: [4353, 7824, 78249, 8724]
Example 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);    }} |
Output:
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]
Reference: https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentLinkedQueue.html#peek–
