LinkedTransferQueue hasWaitingConsumer() method in Java

The Java.util.concurrent.LinkedTransferQueue.hasWaitingConsumer() method always returns true if there is at least one consumer in the queue waiting to receive an element via BlockingQueue.take() or timed poll. The returned value represents a momentary state of affairs.

Syntax

public boolean hasWaitingConsumer()

Parameters: It does not take in any parameter.

Return Value: This method returns a boolean value which is true if at least one consumer is present in the queue.

Below are a few examples to illustrate the LinkedTransferQueue.hasWaitingConsumer() method:

Example 1:

// Java code to demonstrate
// hasWaitingConsumer() method

import java.util.concurrent.LinkedTransferQueue;

class GFG {
    public static void main(String args[])
    {
        LinkedTransferQueue<String> LTQ
            = new LinkedTransferQueue<String>();

        LTQ.add("Geeks");
        LTQ.add("For");
        LTQ.add("Geeks");
        LTQ.add("GeeksForGeeks");

        System.out.println(LTQ.hasWaitingConsumer());
    }
}

Output:

false

Example 2:

// Java code to demonstrate
// hasWaitingConsumer() method

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.LinkedTransferQueue;

public class GFG {

    LinkedTransferQueue<Integer> LTQ
        = new LinkedTransferQueue<>();

    class LTQProducer implements Runnable {

        @Override
        public void run()
        {
            for (int i = 0; i < 3; i++) {
                try {
                    System.out.println("Producer is"
                                       + " waiting to transfer");
                    LTQ.transfer(i);
                    System.out.println("Producer transferred"
                                       + " element: "
                                       + i);
                    System.out.println("Is there any consumer"
                                       + " still waiting to"
                                       + " receive an element"
                                       + " after transfer -> "
                                       + LTQ.hasWaitingConsumer());
                }
                catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    class LTQConsumer implements Runnable {
        int id;
        LTQConsumer(int id)
        {
            this.id = id;
        }

        @Override
        public void run()
        {
            try {
                System.out.println("Consumer "
                                   + id
                                   + " is waiting to "
                                   + "take an element.");
                System.out.println("Is there any consumer"
                                   + " still waiting to"
                                   + " receive an element"
                                   + " after transfer -> "
                                   + LTQ.hasWaitingConsumer());
                Integer s = LTQ.take();
                System.out.println("Consumer "
                                   + id
                                   + " received Element: "
                                   + s);
            }
            catch (InterruptedException e) {
                System.out.println(e);
            }
        }
    }

    // Driver code
    public static void main(String[] args)
        throws InterruptedException
    {
        GFG ob = new GFG();

        ExecutorService exService
            = Executors.newFixedThreadPool(3);

        LTQProducer p = ob.new LTQProducer();
        LTQConsumer c1 = ob.new LTQConsumer(0);
        LTQConsumer c2 = ob.new LTQConsumer(1);

        exService.execute(p);
        exService.execute(c1);
        exService.execute(c2);

        exService.shutdown();
    }
}

Output:

Producer is waiting to transfer
Consumer 0 is waiting to take an element.
Is there any consumer waiting to take an element -> false
Consumer 1 is waiting to take an element.
Is there any consumer waiting to take an element -> false
Consumer 0 received Element: 0
Producer transferred element: 0
Is there any consumer still waiting to receive an element after transfer -> true
Producer is waiting to transfer
Producer transferred element: 1
Consumer 1 received Element: 1
Is there any consumer still waiting to receive an element after transfer -> false
Producer is waiting to transfer