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DelayQueue iterator() method in Java with Examples

  • Last Updated : 12 May, 2021

The iterator() method of DelayQueue is used to return an iterator over all the elements in the DelayQueue. These elements can be expired or unexpired.

public Iterator iterator ()

Parameters: This method does not accept any parameter.
Returns: This method returns an iterator over elements in this delayqueue.
Below program to illustrate DelayQueue iterator() in Java:

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// Java Program Demonstrate DelayQueue iterator() 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)
    { = name;
        this.time = System.currentTimeMillis()
                    + delayTime;
    // Implementing getDelay() method of Delayed
    public long getDelay(TimeUnit unit)
        long diff = time - System.currentTimeMillis();
        return unit.convert(diff, TimeUnit.MILLISECONDS);
    // Implementing compareTo() method of Delayed
    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
    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));
        DQ.add(new DelayObject("C", 3));
        DQ.add(new DelayObject("D", 4));
        // Creating an iterator
        Iterator val = DQ.iterator();
        // print the value after iterating DelayQueue
        System.out.println("The iterator values are: ");
        while (val.hasNext()) {
The iterator values are: 

{ A, time=1545818784540}

{ B, time=1545818784541}

{ C, time=1545818784542}

{ D, time=1545818784543}


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