LinkedListQueue.java

/*
 * 
 * This code is written for Queue tutorial
 * The comment won't make sense unless you read the slide that goes with it
 * 
 * Go to Vumari.com to find slides
 * 
 */
public class LinkedListQueue {
	
	private static class Node{
		int data;
		Node next;
		
		public Node(int data) {
			this.data = data;
			next = null;
		}
	}
	
	private Node head, tail;
	
	private int size = 0;
	
	public void enequeue(int aData){
		
		Node aNewNode = new Node(aData);
		
		if(head == null){//for the first time
			head = aNewNode;
			tail = aNewNode;
		}else{
			//second & more times
			tail.next = aNewNode; //previous node says hello to new guy
			tail = aNewNode; //point to the new end;
		}
		size++;
	}
	
	public int dequeue(){
		
		if(isEmpty()){
			throw new NullPointerException("There is nothing to dequeue from this queue.");
		}
		
		int temp = head.data;
		head = head.next;
		
		size--;
		return temp;
	}
	
	public boolean isEmpty(){
		//if any of the pointer head or tail is null, its empty
		return head == null;
	}
	
	public int getSize(){
		return size;
	}
	
	@Override
	public String toString() {
	
		StringBuilder queueSnapshot = new StringBuilder();
		
		Node printerGuy = head;
		
		while(printerGuy!=null){ //even if the head was null, we will get empty string but not any exception
			queueSnapshot.append(printerGuy.data + ", ");
			printerGuy = printerGuy.next;
		}
				
		return queueSnapshot.toString().replaceAll(", $", "");
	}		
}