ConcurrentLinkedQueue peek() method in Java

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–