The poll() method of DelayQueue is used to retrieve head of the DelayQueue. This method also removes the head from the DelayQueue. Thus when poll method is called, DelayQueue size is reduced by one.
Syntax:
public E poll ()
Parameters:
This method does not accept any parameter.
Returns:
This method returns head of the DelayQueue and also removes it from this DelayQueue.
Exception:
Null Pointer Exception: if head is not present, this function will return null.
Below program to illustrate DelayQueue poll() in Java:
Example:
Java
// Java Program Demonstrate DelayQueue poll() methodimport java.util.concurrent.*;import java.util.*;// The DelayObject for DelayQueue// It must implement Delayed and// its getDelay() and compareTo() methodclass DelayObject implements Delayed { private String name; private long time; // Constructor of DelayObject public DelayObject(String name, long delayTime) { this.name = name; this.time = System.currentTimeMillis() + delayTime; } // Implementing getDelay() method of Delayed @Override public long getDelay(TimeUnit unit) { long diff = time - System.currentTimeMillis(); return unit.convert(diff, TimeUnit.MILLISECONDS); } // Implementing compareTo() method of Delayed @Override public int compareTo(Delayed obj) { if (this.time < ((DelayObject)obj).time) { return -1; } if (this.time > ((DelayObject)obj).time) { return 1; } return 0; } // Implementing toString() method of Delayed @Override public String toString() { return "\n{" + " " + name + ", time=" + time + "}"; }}// Driver Classpublic class GFG { public static void main(String[] args) throws InterruptedException { // create object of DelayQueue // using DelayQueue() constructor BlockingQueue<DelayObject> DQ = new DelayQueue<DelayObject>(); // Add numbers to end of DelayQueue // using add() method DQ.add(new DelayObject("A", 1)); DQ.add(new DelayObject("B", 2)); DQ.add(new DelayObject("C", 3)); DQ.add(new DelayObject("D", 4)); // Print delayqueue System.out.println("Original DelayQueue: " + DQ + "\n"); // Print size of original DelayQueue System.out.println("Original DelayQueue size: " + DQ.size() + "\n"); // poll() method for returning head of the DelayQueue System.out.println("Head of the DelayQueue: " + DQ.poll()); // print DelayQueue size after poll method System.out.println("\nAfter poll() method, DelayQueue size: " + DQ.size()); }} |
Output:
Original DelayQueue: [
{ A, time=1545817370442},
{ B, time=1545817370443},
{ C, time=1545817370444},
{ D, time=1545817370445}]
Original DelayQueue size: 4
Head of the DelayQueue:
{ A, time=1545817370442}
After poll() method, DelayQueue size: 3
Example:
Java
// Java Program Demonstrate DelayQueue poll() methodimport java.util.concurrent.*;import java.util.*;// The DelayObject for DelayQueue// It must implement Delayed and// its getDelay() and compareTo() methodclass DelayObject implements Delayed { private String name; private long time; // Constructor of DelayObject public DelayObject(String name, long delayTime) { this.name = name; this.time = System.currentTimeMillis() + delayTime; } // Implementing getDelay() method of Delayed @Override public long getDelay(TimeUnit unit) { long diff = time - System.currentTimeMillis(); return unit.convert(diff, TimeUnit.MILLISECONDS); } // Implementing compareTo() method of Delayed @Override public int compareTo(Delayed obj) { if (this.time < ((DelayObject)obj).time) { return -1; } if (this.time > ((DelayObject)obj).time) { return 1; } return 0; } // Implementing toString() method of Delayed @Override public String toString() { return "\n{" + " " + name + ", time=" + time + "}"; }}// Driver Classpublic class GFG { public static void main(String[] args) throws InterruptedException { // create object of DelayQueue // using DelayQueue() constructor BlockingQueue<DelayObject> DQ = new DelayQueue<DelayObject>(); // Print size of original DelayQueue System.out.println("Original DelayQueue size: " + DQ.size() + "\n"); // poll() method for returning head of the DelayQueue System.out.println("Head of the DelayQueue: " + DQ.poll()); }} |
Output:
Original DelayQueue size: 0 Head of the DelayQueue: null
