Generic Queue Using Linked List And Iterator - Coursera Algorithms

To make the stack generic and to hide the internal representation of a queue from client, we can use Generics and Iterator.

Following is the program:

	package queues;
	import java.util.Iterator;
	public class GenericQueueLLItr<Item> implements Iterable<Item> {
	Node first;
	Node last;
	static int size;
	public class Node{
	Item value;
	Node next;
	public Node(Item s) {
	this.value = s;
	}
	}
	public class ListIterator implements Iterator<Item>{
	private Node current = first;
	@Override
	public boolean hasNext() {
	return (current!=null);
	}
	@Override
	public Item next() {
	Item val = current.value;
	current = current.next;
	return val;
	}
	}
	@Override
	public Iterator<Item> iterator() {
	return new ListIterator();
	}
	public void enqueue(Item s) {
	Node prevLast = last;
	last = new Node(s);
	if(!isEmpty())
	prevLast.next = last;
	else {
	first = last;
	}
	size++;
	}
	public Item dequeue() {
	if(isEmpty()) {
	System.out.println("queue empty");
	return null;
	}
	Item s = first.value;
	first = first.next;
	size--;
	return s;
	}
	public boolean isEmpty() {
	return (first==null);
	}
	public int size() {
	return size;
	}
	public void print() {
	System.out.println("==========================");
	Node n = first;
	while(n!=null) {
	System.out.println(n.value);
	n = n.next;
	}
	}
	public static void main(String[] args) {
	//===========String===============
	GenericQueueLLItr<String> queue = new GenericQueueLLItr<String>();
	queue.enqueue("to");
	queue.enqueue("be");
	queue.enqueue("or");
	queue.enqueue("not");
	queue.enqueue("to");
	queue.enqueue("be");
	//queue.print();
	System.out.println("-------------Iterator-----------");
	for(String s: queue) {
	System.out.println(s);
	}
	System.out.println("DQd "+queue.dequeue());
	System.out.println("DQd "+queue.dequeue());
	System.out.println("DQd "+queue.dequeue());
	System.out.println("DQd "+queue.dequeue());
	System.out.println("DQd "+queue.dequeue());
	System.out.println("DQd "+queue.dequeue());
	System.out.println("DQd "+queue.dequeue());
	queue.print();
	//===========Integer===============
	GenericQueueLLItr<Integer> queueInt = new GenericQueueLLItr<>();
	queueInt.enqueue(1);
	queueInt.enqueue(2);
	queueInt.enqueue(3);
	queueInt.enqueue(4);
	queueInt.enqueue(5);
	queueInt.enqueue(6);
	//queueInt.print();
	System.out.println("-------------Iterator-----------");
	for(Integer i: queueInt) {
	System.out.println(i);
	}
	System.out.println("DQd "+queueInt.dequeue());
	System.out.println("DQd "+queueInt.dequeue());
	System.out.println("DQd "+queueInt.dequeue());
	System.out.println("DQd "+queueInt.dequeue());
	System.out.println("DQd "+queueInt.dequeue());
	System.out.println("DQd "+queueInt.dequeue());
	System.out.println("DQd "+queueInt.dequeue());
	queueInt.print();
	}
	}

view raw GenericQueueLLItr.java hosted with ❤ by GitHub