Added LinkedListSort.Java

Adding a sort linked list function that takes in the head of the linked list and returns the list, as described in open issue: TheAlgorithms#2450.

Author: vicentecortes23

src/main/java/com/thealgorithms/sorts/LinkedListSort.java

@@ -0,0 +1,86 @@
+//Author: Vicente Cortes
+//Github: https://github.com/vicentecortes23
+
+//https://en.wikipedia.org/wiki/Bubble_sort
+//This java program sorts a LinkedList given a head pointer, as described in the issue https://github.com/TheAlgorithms/Java/issues/2450.
+package com.thealgorithms.sorts;
+
+
+public class LinkedListSort {
+
+    public static class Node {
+        int value;
+        Node next;
+        Node prev;
+
+       public Node(int val)
+        {
+            this.value = val;
+            this.next = null;
+            this.prev = null;
+        }
+    
+        public void push(int val){
+
+            Node newNode = new Node(val);
+
+            Node currentNode = this;
+
+            while(currentNode.next != null){
+                currentNode = currentNode.next;
+            }
+
+            currentNode.next = newNode;
+            newNode.prev = currentNode;
+        }
+
+    }
+
+    public Node sortList(Node node){
+
+        //in order to sort these two lists, we will use bubble sort starting from the head node.
+        Node thisNode = node;
+        Node nextNode = null;
+
+        while(thisNode != null){
+
+            nextNode = thisNode.next;
+
+            while(nextNode != null){
+
+                if (thisNode.value > nextNode.value){
+                    int temp  = thisNode.value;
+                    thisNode.value = nextNode.value;
+                    nextNode.value = temp;
+                }
+
+                nextNode = nextNode.next;
+
+            }
+            thisNode = thisNode.next;
+        }
+
+        return node;
+    }
+
+    public static void main(String args[]){
+
+        LinkedListSort sorter = new LinkedListSort();
+
+        Node head = new Node(5);
+        head.push(3);
+        head.push(6);
+        head.push(7);
+        head.push(1);
+        head.push(2);
+        head.push(8);
+        head.push(4);
+
+        head = sorter.sortList(head);
+
+        while(head != null){
+            System.out.print(head.value + " ");
+            head = head.next;
+        }
+    }    
+};