DelayQueue offer() method in Java with Examples

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}]