import java.util.LinkedList; import java.util.Queue; /**  * Demonstrate Queue interface methods with LinkedList implementation.  * @author javaguides.net  *  */ public class QueueSizeSearchFrontExample { public static void main(String[] args) { Queue<String> elementQueue = new LinkedList<>(); elementQueue.add("element1"); elementQueue.add("element2"); elementQueue.add("element3"); elementQueue.add("element4"); System.out.println("WaitingQueue : " + elementQueue); // Check is a Queue is empty System.out.println("is waitingQueue empty? : " + elementQueue.isEmpty()); // Find the size of the Queue System.out.println("Size of waitingQueue : " + elementQueue.size()); // Check if the Queue contains an element String name = "Johnny"; if(elementQueue.contains(name)) { System.out.println("WaitingQueue contains " + name); } else { System.out.println("Waiting Queue doesn't contain " + name); } // Get the element at the front of the Queue without removing it using element() // The element() method throws NoSuchElementException if the Queue is empty String firstElementInTheWaitingQueue = elementQueue.element(); System.out.println("Waiting Queue (element()) : " + firstElementInTheWaitingQueue); // Get the element at the front of the Queue without removing it using peek() // The peek() method is similar to element() except that it returns null if the Queue is empty firstElementInTheWaitingQueue = elementQueue.peek(); System.out.println("Waiting Queue : " + firstElementInTheWaitingQueue); } }