Doubly linked list implementation and array based implementation in java

Doubly linked list implementation

package com.java2novice.ds.linkedlist;

import java.util.NoSuchElementException;

public class DoublyLinkedListImpl

{

    private Node head;

    private Node tail;

    private int size;

    public DoublyLinkedListImpl()

    {

        size = 0;

    }

      private class Node

    {

        E element;

        Node next;

        Node prev;

        public Node(E element, Node next, Node prev)

       {

            this.element = element;

            this.next = next;

            this.prev = prev;

        }

    }

    public int size() { return size; }

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

    public void addFirst(E element)

     {

        Node tmp = new Node(element, head, null);

        if(head != null ) {head.prev = tmp;}

        head = tmp;

        if(tail == null) { tail = tmp;}

        size++;

        System.out.println("adding: "+element);

    }

    public void addLast(E element)

    {

        Node tmp = new Node(element, null, tail);

        if(tail != null) {tail.next = tmp;}

        tail = tmp;

        if(head == null) { head = tmp;}

        size++;

        System.out.println("adding: "+element);

    }

      public void iterateForward()

       {

        System.out.println("iterating forward..");

        Node tmp = head;

        while(tmp != null)

        {

            System.out.println(tmp.element);

            tmp = tmp.next;

        }

    }

    public void iterateBackward()

    { 

        System.out.println("iterating backword..");

        Node tmp = tail;

        while(tmp != null)

        {

            System.out.println(tmp.element);

            tmp = tmp.prev;

        }

    }

    public E removeFirst()

    {

        if (size == 0) throw new NoSuchElementException();

        Node tmp = head;

        head = head.next;

        head.prev = null;

        size--;

        System.out.println("deleted: "+tmp.element);

        return tmp.element;

    }   

    public E removeLast()

    {

        if (size == 0) throw new NoSuchElementException();

        Node tmp = tail;

        tail = tail.prev;

        tail.next = null;

        size--;

        System.out.println("deleted: "+tmp.element);

        return tmp.element;

    }

    public static void main(String a[])

   {

             DoublyLinkedListImpl dll = new         DoublyLinkedListImpl();

        dll.addFirst(10);

        dll.addFirst(34);

        dll.addLast(56);

        dll.addLast(364);

        dll.iterateForward();

        dll.removeFirst();

        dll.removeLast();

        dll.iterateBackward();

    }

}

Queue introduction & array based implementation

package com.java2novice.ds.queue;

public class QueueImpl

  {

    private int capacity;

    int queueArr[];

    int front = 0;

    int rear = -1;

    int currentSize = 0;

     public QueueImpl(int queueSize)

     {

        this.capacity = queueSize;

        queueArr = new int[this.capacity];

    }

    public void enqueue(int item)

      {

        if (isQueueFull())

         {

            System.out.println("Overflow ! Unable to add element: "+item);

        }

          else

           {

            rear++;

            if(rear == capacity-1)

            {

                rear = 0;

            }

            queueArr[rear] = item;

            currentSize++;

            System.out.println("Element " + item+ " is pushed to Queue !");

        }

    }    

    public void dequeue()

    {

        if (isQueueEmpty())

        {

            System.out.println("Underflow ! Unable to remove element from Queue");

        }

          else

          {

            front++;

            if(front == capacity-1)

            {

                System.out.println("Pop operation done ! removed: "+queueArr[front-1]);

                front = 0;

            }

            else

            {

                System.out.println("Pop operation done ! removed: "+queueArr[front-1]);

            }

            currentSize--;

        }

   }

    public boolean isQueueFull()

     {

        boolean status = false;

        if (currentSize == capacity)

       {

            status = true;

        }

        return status;

    }

    public boolean isQueueEmpty()

      {

        boolean status = false;

        if (currentSize == 0)

         {

            status = true;

        }

        return status;

    }

    public static void main(String a[])

    {

        QueueImpl queue = new QueueImpl(4);

        queue.enqueue(4);

        queue.dequeue();

        queue.enqueue(56);

        queue.enqueue(2);

        queue.enqueue(67);

        queue.dequeue();

        queue.dequeue();

        queue.enqueue(24);

        queue.dequeue();

        queue.enqueue(98);

        queue.enqueue(45);

        queue.enqueue(23);

        queue.enqueue(435);

    }

}