package DataStructures.Queues; import java.util.ArrayList; /** * This class implements a GenericArrayListQueue. * *

A GenericArrayListQueue data structure functions the same as any specific-typed queue. The * GenericArrayListQueue holds elemets of types to-be-specified at runtime. The elements that are * added first are the first to be removed (FIFO) New elements are added to the back/rear of the * queue. */ public class GenericArrayListQueue { /** The generic ArrayList for the queue T is the generic element */ ArrayList _queue = new ArrayList(); /** * Checks if the queue has elements (not empty) * * @return True if the queue has elements. False otherwise. */ private boolean hasElements() { return !_queue.isEmpty(); } /** * Checks what's at the front of the queue * * @return If queue is not empty, element at the front of the queue. Otherwise, null */ public T peek() { T result = null; if (this.hasElements()) { result = _queue.get(0); } return result; } /** * Inserts an element of type T to the queue. * * @param element of type T to be added * @return True if the element was added successfully */ public boolean add(T element) { return _queue.add(element); } /** * Retrieve what's at the front of the queue * * @return If queue is not empty, element retrieved. Otherwise, null */ public T poll() { T result = null; if (this.hasElements()) { result = _queue.remove(0); } return result; } /** * Main method * * @param args Command line arguments */ public static void main(String[] args) { GenericArrayListQueue queue = new GenericArrayListQueue(); System.out.println("Running..."); assert queue.peek() == null; assert queue.poll() == null; assert queue.add(1) == true; assert queue.peek() == 1; assert queue.add(2) == true; assert queue.peek() == 1; assert queue.poll() == 1; assert queue.peek() == 2; assert queue.poll() == 2; assert queue.peek() == null; assert queue.poll() == null; System.out.println("Finished."); } }