BlockingQueue poll() method in Java with examples
Last Updated :
14 Oct, 2019
The
poll(long timeout, TimeUnit unit) method of
BlockingQueue interface returns the head of BlockingQueue by removing that element from the queue. It can be said that this method retrieves and removes element from head of this LinkedBlockingQueue. If queue is empty, then poll() method will wait till a specified time for an element to become available.
Syntax:
public E poll(long timeout, TimeUnit unit) throws
Parameters: This method takes two mandatory parameters:
- timeout- how long to wait, in units of unit.
- unit- a TimeUnit for the timeout parameter.
Return Value: This method retrieves and removes element from head of this LinkedBlockingQueue, or null if the specified waiting time elapses before an element is available.
Exception This method throws
InterruptedException if method interrupted while waiting for an element to become available.
Note: The
poll() method of
BlockingQueue has been inherited from the
Queue class in Java.
Below programs illustrates poll(long timeout, TimeUnit unit) method of BlockingQueue:
Program 1:
Java
// Java program to demonstrate
// poll(long timeout, TimeUnit unit)
// method of LinkedBlockingQueue
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;
public class GFG {
public static void main(String[] args)
throws InterruptedException
{
// define capacity of BlockingQueue
int capacityOfQueue = 4;
// create object of BlockingQueue
BlockingQueue<String> BQ
= new LinkedBlockingQueue<String>(capacityOfQueue);
// Add element to BlockingQueue
BQ.add("Ravi");
BQ.add("Suraj");
BQ.add("Harsh");
// print elements of queue
System.out.println("Items in Queue are " + BQ);
// Try to poll elements from BQ
// using poll(long timeout, TimeUnit unit) method
System.out.println("Removing item From head: "
+ BQ.poll(5, TimeUnit.SECONDS));
// print queue details
System.out.println("Now Queue Contains" + BQ);
// using poll(long timeout, TimeUnit unit) method
System.out.println("Removing item From head: "
+ BQ.poll(5, TimeUnit.SECONDS));
// print queue details
System.out.println("Now Queue Contains" + BQ);
// using poll(long timeout, TimeUnit unit) method
System.out.println("Removing item From head: "
+ BQ.poll(5, TimeUnit.SECONDS));
// print queue details
System.out.println("Now Queue Contains" + BQ);
// using poll(long timeout, TimeUnit unit) method
System.out.println("Removing item From head: "
+ BQ.poll(5, TimeUnit.SECONDS));
// print queue details
System.out.println("Now Queue Contains" + BQ);
}
}
Output:
Items in Queue are [Ravi, Suraj, Harsh]
Removing item From head: Ravi
Now Queue Contains[Suraj, Harsh]
Removing item From head: Suraj
Now Queue Contains[Harsh]
Removing item From head: Harsh
Now Queue Contains[]
Removing item From head: null
Now Queue Contains[]
Program 2:
Java
// Java program to demonstrate
// poll(long timeout, TimeUnit unit)
// method of LinkedBlockingQueue
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;
public class GFG {
public static void main(String[] args)
throws InterruptedException
{
// define capacity of BlockingQueue
int capacityOfQueue = 2;
// create object of BlockingQueue
BlockingQueue<String> BQ
= new LinkedBlockingQueue<String>(capacityOfQueue);
// Add element to BlockingQueue
BQ.add("Gopal");
BQ.add("GFG");
// print elements of queue
System.out.println("Items in Queue are " + BQ);
// Try to poll elements from BQ
// using poll(long timeout, TimeUnit unit) method
System.out.println("Removing item From head: "
+ BQ.poll(2, TimeUnit.SECONDS));
// print queue details
System.out.println("Now Queue Contains" + BQ);
}
}
Output:
Items in Queue are [Gopal, GFG]
Removing item From head: Gopal
Now Queue Contains[GFG]
Reference:
https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingQueue.html#poll(long, %20java.util.concurrent.TimeUnit)