Doubly linked list sort in java

SortedList.java

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+public class SortedList {  
+
+    //Represent a node of the doubly linked list  
+
+    class Node{  
+        int data;  
+        Node previous;  
+        Node next;  
+
+        public Node(int data) {  
+            this.data = data;  
+        }  
+    }  
+
+    //Represent the head and tail of the doubly linked list  
+    Node head, tail = null;  
+
+    //addNode() will add a node to the list  
+    public void addNode(int data) {  
+        //Create a new node  
+        Node newNode = new Node(data);  
+
+        //If list is empty  
+        if(head == null) {  
+            //Both head and tail will point to newNode  
+            head = tail = newNode;  
+            //head's previous will point to null  
+            head.previous = null;  
+            //tail's next will point to null, as it is the last node of the list  
+            tail.next = null;  
+        }  
+        else {  
+            //newNode will be added after tail such that tail's next will point to newNode  
+            tail.next = newNode;  
+            //newNode's previous will point to tail  
+            newNode.previous = tail;  
+            //newNode will become new tail  
+            tail = newNode;  
+            //As it is last node, tail's next will point to null  
+            tail.next = null;  
+        }  
+    }  
+
+    //sortList() will sort the given list in ascending order  
+    public void sortList() {  
+        Node current = null, index = null;  
+        int temp;  
+        //Check whether list is empty  
+        if(head == null) {  
+            return;  
+        }  
+        else {  
+            //Current will point to head  
+            for(current = head; current.next != null; current = current.next) {  
+                //Index will point to node next to current  
+                for(index = current.next; index != null; index = index.next) {  
+                    //If current's data is greater than index's data, swap the data of current and index  
+                    if(current.data > index.data) {  
+                        temp = current.data;  
+                        current.data = index.data;  
+                        index.data = temp;  
+                    }  
+                }  
+            }  
+        }  
+    }  
+
+    //display() will print out the nodes of the list  
+    public void display() {  
+        //Node current will point to head  
+        Node current = head;  
+        if(head == null) {  
+            System.out.println("List is empty");  
+            return;  
+        }  
+        while(current != null) {  
+            //Prints each node by incrementing the pointer.  
+
+            System.out.print(current.data + " ");  
+            current = current.next;  
+        }  
+        System.out.println();  
+    }  
+
+    public static void main(String[] args) {  
+
+        SortList dList = new SortList();  
+        //Add nodes to the list  
+        dList.addNode(7);  
+        dList.addNode(1);  
+        dList.addNode(4);  
+        dList.addNode(5);  
+        dList.addNode(2);  
+
+        //Displaying original list  
+        System.out.println("Original list: ");  
+        dList.display();  
+
+        //Sorting list  
+        dList.sortList();  
+
+        //Displaying sorted list  
+        System.out.println("Sorted list: ");  
+        dList.display();  
+    }  
+}