LinkedQueue.java

package br.unisinos.queue;

public class LinkedQueue<E> implements Queue<E> {

	protected Node<E> first, last;
	protected int numElements;

	public LinkedQueue() {
		first = last = null;
		numElements = 0;
	}

	public boolean isEmpty() {
		return numElements == 0;
	}

	public boolean isFull() {
		// uma fila com alocação dinâmica nunca estará cheia!
		return false;
	}

	public int numElements() {
		return numElements;
	}

	public void enqueue(E element) {
		Node<E> newNode = new Node<E>(element);
		if (isEmpty())
			first = last = newNode;
		else {
			last.setNext(newNode);
			last = newNode;
		}
		numElements++;
	}

	public E dequeue() throws UnderflowException {
		if (isEmpty())
			throw new UnderflowException();
		E element = first.getElement();
		if (first == last)
			first = last = null;
		else
			first = first.getNext();
		numElements--;
		return element;
	}

	public E front() throws UnderflowException {
		if (isEmpty())
			throw new UnderflowException();
		return first.getElement();
	}

	public E back() {
		if (isEmpty())
			throw new UnderflowException();
		return last.getElement();
	}

	public String toString() {
		if (isEmpty())
			return "[Empty]";
		else {
			String s = "[" + first.getElement();
			Node<E> cur = first.getNext();
			while (cur != null) {
				s += ", " + cur.getElement();
				cur = cur.getNext();
			}
			return s + "]";
		}
	}
}