Add doubly linked list java (#125)

* Add doubly linked list in java

* Add java doubly linked list's link to README.md

linked-lists/README.md

@@ -12,6 +12,7 @@
 ### Java
 
 1. [Singly Linked List](java/singly.java)
+2. [Doubly Linked List](java/doubly.java)
 
 ### JavaScript
 

linked-lists/java/doubly.java

@@ -0,0 +1,77 @@
+class DoublyLinkedList {    
+    class Node{  
+        int item;  
+        Node previous;  
+        Node next;  
+   
+        public Node(int item) {  
+            this.item = item;  
+        }  
+    }  
+
+    Node head, tail = null;  
+    
+    public void addNode(int item) { 
+        Node newNode = new Node(item);  
+   
+        //if list is empty, head and tail points to newNode  
+        if(head == null) {  
+            head = tail = newNode;  
+            //head's previous will be null  
+            head.previous = null;  
+            //tail's next will be null  
+            tail.next = null;  
+        }  
+        else {  
+            //add newNode to the end of list. tail->next set to newNode  
+            tail.next = newNode;  
+            //newNode->previous set to tail  
+            newNode.previous = tail;  
+            //newNode becomes new tail  
+            tail = newNode;  
+            //tail's next point to null  
+            tail.next = null;  
+        }  
+    }  
+     
+    public void printNodes() {   
+        Node current = head;  
+        if(head == null) {  
+            System.out.println("Doubly linked list is empty");  
+            return;  
+        }  
+        System.out.println("The doubly linked list is: ");
+        System.out.print("[ ");  
+        while(current != null) {    
+            System.out.print(current.item + " ");
+            //go to next  
+            current = current.next;  
+        } 
+        System.out.print("]"); 
+    }  
+}
+ 
+public class doubly {
+    public static void main(String [] args){
+        DoublyLinkedList dl_List = new DoublyLinkedList();  
+        
+        dl_List.addNode(5);  
+        dl_List.addNode(7);  
+        dl_List.addNode(1);  
+        dl_List.addNode(17);  
+        dl_List.addNode(27);  
+   
+        dl_List.printNodes();
+        //this will print :
+        /*
+        The doubly linked list is: 
+        [ 5 7 1 17 27 ]
+        */
+    }
+}
+
+/*
+    to run the file:
+    javac doubly.java
+    java doubly
+*/