Added Doubly Linked List in Java

msameerfarooq · msameerfarooq · commit eb6f73fe2d57 · 2020-10-12T22:24:47.000+05:00
diff --git a/Data Structures/Doubly Linked List/Java/Doubly Linked List.java b/Data Structures/Doubly Linked List/Java/Doubly Linked List.java
@@ -0,0 +1,127 @@
+// Java Class for Doubly Linked List
+class Doubly_linkedList
+{
+   Node head; // list head
+  
+    /* Doubly Linked list Node*/
+    class Node
+    {
+      int data;
+      Node prev;
+      Node next;
+  
+      //create a new node using constructor
+      Node(int d) { data = d;
+	}
+}
+  
+// insert a node at the front of the list
+public void insert_front(int new_data)
+{
+   /* 1. allocate node
+   * 2. put in the data */
+   Node new_Node = new Node(new_data);
+  
+   /* 3. Make next of new node as head and previous as NULL */
+   new_Node.next = head;
+   new_Node.prev = null;
+  
+   /* 4. change prev of head node to new node */
+   if (head != null)
+   head.prev = new_Node;
+  
+   /* 5. move the head to point to the new node */
+   head = new_Node;
+}
+//insert a node after the given prev node
+public void Insert_After(Node prev_Node, int new_data)
+{
+   //check that prev node is not null
+   if (prev_Node == null)
+   {
+		System.out.println("The previous node is required,it cannot be NULL ");
+		return;
+	}
+  
+   //allocate new node and set it to data
+   Node newNode = new Node(new_data);
+  
+   //set next of newNode as next of prev node
+   newNode.next = prev_Node.next;
+  
+   //set new node to next of prev node
+   prev_Node.next = newNode;
+  
+   //set prev of newNode as prev node
+   newNode.prev = prev_Node;
+  
+   //set prev of new node's next to newnode
+   if (newNode.next != null)
+   newNode.next.prev = newNode;
+}
+  
+// Add a node at the end of the list
+void insert_end(int new_data)
+{
+   //allocate the node and set the data
+   Node newNode = new Node(new_data);
+   Node last = head; //set last as the head
+   //set next of new node to null since its the last node
+   newNode.next = null;
+  
+   //set new node as head if the list is null
+   if (head == null) 
+   {
+      newNode.prev = null;
+      head = newNode;
+      return;
+   }
+   //if list is not null then traverse it till the last node and set last next to last
+   while (last.next != null)
+		last = last.next;
+  
+   last.next = newNode;           //set last next to new node
+  
+   newNode.prev = last;           //set last as prev of new node
+}
+// display the contents of linked list starting from the given node
+public void displaylist(Node node)
+{
+   Node last = null;
+   while (node != null) 
+   {
+      System.out.print(node.data + "<==>");
+      last = node;
+      node = node.next;
+   }
+   if(node == null)
+   System.out.print("null");
+   System.out.println();
+  
+   }
+}
+class Main{
+   public static void main(String[] args)
+      {
+      /* Start with the empty list */
+      Doubly_linkedList dll = new Doubly_linkedList();
+  
+      // Insert 40.
+      dll.insert_end(40);
+  
+      // Insert 20 at the beginning.
+      dll.insert_front(20);
+  
+      // Insert 10 at the beginning.
+      dll.insert_front(10);
+  
+      // Insert 50 at the end.
+      dll.insert_end(50);
+  
+      // Insert 30, after 20.
+      dll.Insert_After(dll.head.next, 30);
+  
+      System.out.println("Doubly linked list created is as follows: ");
+      dll.displaylist(dll.head);
+      }
+}
