DelayQueue add() method in Java with Examples Last Updated : 14 Jan, 2022 Summarize Comments Improve Suggest changes Share Like Article Like Report The add(E ele) method of DelayQueue class in Java is used to insert the given element into the delay queue and returns true if the element has been successfully inserted. Here, E refers to the type of elements maintained by this DelayQueue collection.Syntax: public boolean add(E ele) Parameters: This method takes only one parameter ele. It refers to the element which will be inserted into the delay queue.Return Value: It returns a boolean value which is true if the element has been added successfully otherwise it returns false.Exception: NullPointerException: This method throws a NullPointerException if a NULL is tried to inserted in this DelayQueue. Below programs illustrate the add() method of DelayQueue class:Program 1: Java // Java program to illustrate the add() // method in Java import java.util.concurrent.DelayQueue; import java.util.concurrent.Delayed; import java.util.concurrent.TimeUnit; public class GFG { public static void main(String args[]) { // Create a DelayQueue instance DelayQueue<Delayed> queue = new DelayQueue<Delayed>(); // Create an instance of Delayed Delayed obj = new Delayed() { public long getDelay(TimeUnit unit) { return 24; // some value is returned } public int compareTo(Delayed o) { if (o.getDelay(TimeUnit.DAYS) > this.getDelay(TimeUnit.DAYS)) return 1; else if (o.getDelay(TimeUnit.DAYS) == this.getDelay(TimeUnit.DAYS)) return 0; return -1; } }; // Use the add() method to add obj to // the empty DelayQueue instance queue.add(obj); System.out.println("Size of the queue : " + queue.size()); } } Output: Size of the queue : 1 Program 2: Program to demonstrate the NullPointerException. Java // Java program to illustrate the Exception // thrown by add() method of // DelayQueue class import java.util.concurrent.DelayQueue; import java.util.concurrent.Delayed; import java.util.concurrent.TimeUnit; public class GFG { public static void main(String args[]) { // Create an instance of DelayQueue DelayQueue<Delayed> queue = new DelayQueue<Delayed>(); // Try to add NULL to the queue try { queue.add(null); } // Catch Exception catch (Exception e) { // Print Exception raised System.out.println(e); } } } Output: java.lang.NullPointerException Comment More infoAdvertise with us Next Article DelayQueue put() method in Java with Examples P psil123 Follow Improve Article Tags : Java Java - util package java-DelayQueue Practice Tags : Java Similar Reads DelayQueue put() method in Java with Examples The put(E ele) method of DelayQueue class in Java is used to inserts a given element into the delay queue container. Hetre, E is the type of element maintained by this DelayQueue container. Syntax: public void put(E ele) Parameters: This method accepts only one parameter ele. It is the element which 2 min read DelayQueue take() method in Java with Examples The take() method of DelayQueue is used to retrieve head of the DelayQueue and also removes it. Thus, the size of the DelayQueue is reduced. This function waits if an element with expired delay is available on this queue. Syntax: public E take () Parameters: This method accepts no parameters.Return 2 min read DelayQueue poll() method in Java with Examples 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 re 3 min read DelayQueue peek() method in Java with Examples The peek() method of DelayQueue is used to retrieve head of the DelayQueue, but does not remove it, as in case of poll() method where head is removed from the DelayQueue. Syntax: public E peek () Parameters: This method does not accept any parameter. Returns: This method returns the head of the Dela 3 min read DelayQueue size() method in Java with Examples The size() method of DelayQueue class in Java is used to return the number of elements present in the given queue. If the number of elements is greater than Integer.MAX_VALUE then Integer.MAX_VALUE is returned as the size of this DelayQueue.Syntax: public int size() Parameters: It does not takes in 1 min read 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 De 2 min read Like