Doubly Linked List written in Java

DoublyLinkedList.java

/**
 * Singly Linked list implementation in Java
 * 
 *  Copy the 3 classes in DList.java, DLinkedList.java and Main.java in order to run the implementation
 * 
 *  Dinesh
 * 
 *   ____________	    _____________       ______________
 *  |item "test1"|	   | item "test2"|      | item "test3" |
 *  |      next  |-------->|        next |----->|        next  |------>null	
 *  |_prev(null) |<--------|prev         |<-----|prev          |
 *  |____________|	   |_____________|	|______________| 	
 *    HEAD                                          TAIL
 *
 * This is a basic implementation for Doubly linked list. More optimization can be implemented.
 * Also more error checking needs to be done.
 * 
 * Sentinal can be added to store head and size information
 **/
 
 /**
  * DListNode.java
  * 
  * */
public class DListNode {
	Object item;
	DListNode prev;
	DListNode next;
}

/**
* DLinkedList.java
*
*/
public class DLinkedList {
	public DListNode head;
	public DListNode tail;
	private int size;
	
	public DLinkedList(){
		size = 0;
		this.head = null;
		this.tail = null;
	}
	
	/**
	 * Inserting new node at the end of the linked list
	 * If there is node node present we will make the first node as out main node 
	 * 
	 * @param item - represent the DListNode item to be added to the linked list
	 */
		public void insertNode(String item) {
			DListNode node = new DListNode();
			node.item = item;
			node.next = null;

			if (this.head == null) {
				this.head = node;
				this.tail = node;
				this.tail.next = null;
				this.tail.prev = null;
				this.size = 1;
			} else {
				DListNode prev = this.tail;
				this.tail.next = node;
				this.tail = node;
				this.tail.prev = prev;
				this.size++;
			}
		}
		
		/**
		 * Adding DListNode at the first location of the linked list
		 * 
		 * @param item - represent item of the DListNode to be added to LL
		 */
		public void insertFirst(String item){
			DListNode node = new DListNode();
			node.item = item;
			node.next = this.head;
			this.head.prev = node;
			this.head = node;
			this.size++;
		}
		
		/**
		 * Adding DListNode at the nth location of the linked list 
		 * if location is greater than half of size traverse from tail
		 * if location is smaller than half of size traverse from head
		 * 
		 * @param item - represent the item of the DListNode to be added to the list
		 * @param position - position at which the DListNode is to be added
		 */
		public void insertNth(String item, int position) {
			int center = (int) Math.floor(size/2);
			DListNode node = new DListNode();
			node.item = item;
			DListNode current = null;
			if (this.head != null && position <= this.size) {
				if(position < center){
					current = head;
					for(int i=1;i<position;i++){
						current = current.next;
					}
				}else{
					current = tail;
					for(int i=size; i>position; i--){
						current = current.prev;
					}
				}
				node.next = current.next;
				current.next.prev = node;
				node.prev = current;
				current.next = node;
				this.size += 1;
			}else{
				System.out.println("Exceeded the linked list size. Current Size: "+size);
			}
		}

		/**
		 * Deleting the first Node from the list
		 */
		public void deleteFirstNode() {
			if(head != null){
				this.head = this.head.next;
				this.head.prev = null;
				this.size--;
			}else{
				System.out.println("Linked list is empty");
			}
		}

		/**
		 * Deleting the last DListNode from the list
		 */
		public void deleteLastNode() {
			if(tail != null){
				this.tail = this.tail.prev;
				this.tail.next = null;
				this.size--;
			}
		}

		/**
		 * Deleting the DListNode from the nth location in the list
		 * 
		 * @param position - location of the DListNode to be deleted
		 */
		public void deleteNthNode(int position) {
			DListNode current = null;
			int center = (int)Math.floor(size/2);
			if(position < size){
				if(position < center){
					current = head;
					for(int i=1; i<position; i++){
						current = current.next;
					}
				}else{
					current = tail;
					for(int i=size-1;i>position;i--){
						current = current.prev;
					}
				}
				current.prev.next = current.next;
				current.next.prev = current.prev;
				size--;
			}else{
				System.out.println("The position is exceeds the linked list size: "+this.size);
			}
		}

		/**
		 * Find if the DListNode exist in the list
		 * 
		 * @param item - item to be found in the list
		 * 
		 */
		public void findNode(String item) {
			DListNode node = this.head;
			boolean found = false;
			for(int i=0;i<size; i++){
				if(node.item.equals(item)){
					System.out.println("Item "+item+" was found at location "+i+" in the linked list");
					found = true;
				}
				node = node.next;
			}
			
			if(!found)
				System.out.println("Item "+item+" was not found in the Linked list");
		}

		/**
		 * Find the DListNode item located at a specific location
		 * 
		 * @param location - Find item at location
		 * 
		 */
		public void findNodeAt(int location) {
			DListNode node = this.head;
			if(head !=null && location<= size){
				for(int i=0;i<location;i++){
					node = node.next;
				}
				System.out.println("DListNode item at location "+location+" is "+node.item);
			}
		}

		/**
		 * Find the item at the last location
		 * 
		 */
		public void findLastNode() {
			if(tail != null){
				System.out.println("DListNode item at last location is "+tail.item);
			}
		}


		/**
		 * Printing all the items in the list
		 */
		public void printDListNodes() {
			if (this.size < 1)
				System.out.println("There are no Nodes in the Doubly linked list");
			else {
				DListNode current = this.head;
				for (int i = 0; i < this.size; i++) {
					if(current.prev == null)
						System.out.println("Node " + current.item + " is at location " + i + " : Previous Node: null : Next Node: "+current.next.item);
					else if(current.next == null)
						System.out.println("Node " + current.item + " is at location " + i + " : Previous Node: "+current.prev.item + " : Next Node: null");
					else System.out.println("Node " + current.item + " is at location " + i + " : Previous Node: "+current.prev.item + " : Next Node: "+current.next.item);
					current = current.next;
				}
				System.out.println("Head: "+ this.head.item + " and Tail:"+ this.tail.item);
			}
		}
		
	
	/**
	 * Get linked list size
	 * 
	 * @return
	 */
	public int getSize(){
		return size;
	}
}

/**
* Main.java
*
**/

public class Main {

	public static void main(String[] args) {
		System.out.println("Doubly Linked list");
		DLinkedList dlist = new DLinkedList();
		
		dlist.insertNode("test1");
		dlist.insertNode("test2");
		dlist.insertNode("test3");
		dlist.insertNode("test4");
		dlist.insertNode("test5");
		dlist.insertNode("test6");
		dlist.insertNode("test7");
		dlist.printDListNodes();
		
		System.out.println();
		
		System.out.println("Finding item test2 in the Linked list");
		dlist.findNode("test2");
		System.out.println("Finding item nonExist in the Lineked list");
		dlist.findNode("nonExist");
		
		System.out.println();
		
		System.out.println("Finding item at location 4");
		dlist.findNodeAt(4);
		
		System.out.println();
		System.out.println("Finding item at last location ");
		dlist.findLastNode();
		System.out.println();
		
		System.out.println("Adding test1st at start of the Node");
		dlist.insertFirst("test1st");
		dlist.printDListNodes();
		
		System.out.println();
		
		System.out.println("Adding testNth at 2nd Location");
		dlist.insertNth("testNth", 2);
		dlist.printDListNodes();
		
		System.out.println();
		
		System.out.println("Adding testNth at 6th Location");
		dlist.insertNth("testNth2", 6);
		dlist.printDListNodes();
		
		System.out.println();
		
		System.out.println("Deleting first node");
		dlist.deleteFirstNode();
		dlist.printDListNodes();
		
		System.out.println();
		
		System.out.println("Deleting last node");
		dlist.deleteLastNode();
		dlist.printDListNodes();
		
		System.out.println();
		
		System.out.println("Deleting 4th node");
		dlist.deleteNthNode(4);
		dlist.printDListNodes();

	}

}


/**
* OUTPUT
*
* Doubly Linked list
* Node test1 is at location 0 : Previous Node: null : Next Node: test2
* Node test2 is at location 1 : Previous Node: test1 : Next Node: test3
* Node test3 is at location 2 : Previous Node: test2 : Next Node: test4
* Node test4 is at location 3 : Previous Node: test3 : Next Node: test5
* Node test5 is at location 4 : Previous Node: test4 : Next Node: test6
* Node test6 is at location 5 : Previous Node: test5 : Next Node: test7
* Node test7 is at location 6 : Previous Node: test6 : Next Node: null
* Head: test1 and Tail:test7
*
* Finding item test2 in the Linked list
* Item test2 was found at location 1 in the linked list
* Finding item nonExist in the Lineked list
* Item nonExist was not found in the Linked list 
*
* Finding item at location 4
* DListNode item at location 4 is test5
*
* Finding item at last location 
* DListNode item at last location is test7
*
* Adding test1st at start of the Node
* Node test1st is at location 0 : Previous Node: null : Next Node: test1
* Node test1 is at location 1 : Previous Node: test1st : Next Node: test2
* Node test2 is at location 2 : Previous Node: test1 : Next Node: test3
* Node test3 is at location 3 : Previous Node: test2 : Next Node: test4
* Node test4 is at location 4 : Previous Node: test3 : Next Node: test5
* Node test5 is at location 5 : Previous Node: test4 : Next Node: test6
* Node test6 is at location 6 : Previous Node: test5 : Next Node: test7
* Node test7 is at location 7 : Previous Node: test6 : Next Node: null
* Head: test1st and Tail:test7
*
* Adding testNth at 2nd Location
* Node test1st is at location 0 : Previous Node: null : Next Node: test1
* Node test1 is at location 1 : Previous Node: test1st : Next Node: testNth
* Node testNth is at location 2 : Previous Node: test1 : Next Node: test2
* Node test2 is at location 3 : Previous Node: testNth : Next Node: test3
* Node test3 is at location 4 : Previous Node: test2 : Next Node: test4
* Node test4 is at location 5 : Previous Node: test3 : Next Node: test5
* Node test5 is at location 6 : Previous Node: test4 : Next Node: test6
* Node test6 is at location 7 : Previous Node: test5 : Next Node: test7
* Node test7 is at location 8 : Previous Node: test6 : Next Node: null
* Head: test1st and Tail:test7
*
* Adding testNth at 6th Location
* Node test1st is at location 0 : Previous Node: null : Next Node: test1
* Node test1 is at location 1 : Previous Node: test1st : Next Node: testNth
* Node testNth is at location 2 : Previous Node: test1 : Next Node: test2
* Node test2 is at location 3 : Previous Node: testNth : Next Node: test3
* Node test3 is at location 4 : Previous Node: test2 : Next Node: test4
* Node test4 is at location 5 : Previous Node: test3 : Next Node: testNth2
* Node testNth2 is at location 6 : Previous Node: test4 : Next Node: test5
* Node test5 is at location 7 : Previous Node: testNth2 : Next Node: test6
* Node test6 is at location 8 : Previous Node: test5 : Next Node: test7
* Node test7 is at location 9 : Previous Node: test6 : Next Node: null
* Head: test1st and Tail:test7
*
* Deleting first node
* Node test1 is at location 0 : Previous Node: null : Next Node: testNth
* Node testNth is at location 1 : Previous Node: test1 : Next Node: test2
* Node test2 is at location 2 : Previous Node: testNth : Next Node: test3
* Node test3 is at location 3 : Previous Node: test2 : Next Node: test4
* Node test4 is at location 4 : Previous Node: test3 : Next Node: testNth2
* Node testNth2 is at location 5 : Previous Node: test4 : Next Node: test5
* Node test5 is at location 6 : Previous Node: testNth2 : Next Node: test6
* Node test6 is at location 7 : Previous Node: test5 : Next Node: test7
* Node test7 is at location 8 : Previous Node: test6 : Next Node: null
* Head: test1 and Tail:test7
*
* Deleting last node
* Node test1 is at location 0 : Previous Node: null : Next Node: testNth
* Node testNth is at location 1 : Previous Node: test1 : Next Node: test2
* Node test2 is at location 2 : Previous Node: testNth : Next Node: test3
* Node test3 is at location 3 : Previous Node: test2 : Next Node: test4
* Node test4 is at location 4 : Previous Node: test3 : Next Node: testNth2
* Node testNth2 is at location 5 : Previous Node: test4 : Next Node: test5
* Node test5 is at location 6 : Previous Node: testNth2 : Next Node: test6
* Node test6 is at location 7 : Previous Node: test5 : Next Node: null
* Head: test1 and Tail:test6
*
* Deleting 4th node
* Node test1 is at location 0 : Previous Node: null : Next Node: testNth
* Node testNth is at location 1 : Previous Node: test1 : Next Node: test2
* Node test2 is at location 2 : Previous Node: testNth : Next Node: test3
* Node test3 is at location 3 : Previous Node: test2 : Next Node: testNth2
* Node testNth2 is at location 4 : Previous Node: test3 : Next Node: test5
* Node test5 is at location 5 : Previous Node: testNth2 : Next Node: test6
* Node test6 is at location 6 : Previous Node: test5 : Next Node: null
* Head: test1 and Tail:test6
*
**/