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DelayQueue offer() method in Java with Examples

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  • Difficulty Level : Basic
  • Last Updated : 20 May, 2021
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The offer() method of DelayQueue is used to insert specified element in the delay queue. It acts similar to add() method of DelayQueue.
Syntax: 
 

public boolean offer (E e)

Parameters: 
DelayQueue accepts only those elements that belong to a class of type Delayed. So, this element E should be of type Delayed.
Returns: 
This method does not return anything.
Exception: 
Null pointer Exception: if the specified element is null.
Below program to illustrate DelayQueue offer() in Java:
Example: 
 

Java




// Java Program Demonstrate DelayQueue offer() method
 
import java.util.concurrent.*;
import java.util.*;
 
// The DelayObject for DelayQueue
// It must implement Delayed and
// its getDelay() and compareTo() method
class 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 Class
public 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));
 
        // Print delayqueue
        System.out.println("Original DelayQueue: "
                           + DQ + "\n");
 
        // Now insert elements using offer method
        DQ.offer(new DelayObject("C", 10));
        DQ.offer(new DelayObject("D", 11));
        DQ.offer(new DelayObject("E", 15));
        DQ.offer(new DelayObject("F", 17));
 
        // print queue
        System.out.println("After insertion DelayQueue: "
                           + DQ);
    }
}

Output: 

Original DelayQueue: [
{ A, time=1545817395066}, 
{ B, time=1545817395067}]

After insertion DelayQueue: [
{ A, time=1545817395066}, 
{ B, time=1545817395067}, 
{ C, time=1545817395076}, 
{ D, time=1545817395077}, 
{ E, time=1545817395081}, 
{ F, time=1545817395083}]

 


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