Linked List removal of Duplicates

 package samples.test;

import java.util.ArrayList;
import java.util.List;

class Node {
    Node next;
    int data;

    public Node(int data) {
        this.data = data;
    }
}

public class LinkedList {
    Node head;

    public void append(int data) {
        if (head == null) {
            head = new Node(data);
            return;
        }
        Node current = head;
        while (current.next != null) {
            current = current.next;
        }

        current.next = new Node(data);
    }

    public void prepend(int data) {
        Node newHead = new Node(data);
        newHead.next = head;
        head = newHead;
    }

    public void deleteWithValue(int data) {
        if (head == null) return;
        if (head.data == data) {
            head = head.next;
            return;
        }
        Node current = head;
        while (current.next != null) {
            if (current.next.data == data) {
                current.next = current.next.next;
                return;
            }
            current = current.next;
        }

    }


    List<Integer> removeDuplicates() {
        List<Integer> values = new ArrayList<>();
        Node temp = head, prev = head;
        while (temp != null) {
            if (temp.data != prev.data) {
                values.add(prev.data);
                prev = temp;
            }
            temp = temp.next;
        }
        if (prev != temp) {
            values.add(prev.data);
            prev.next = null;
        }

        return values;
    }

    public void display() {
        Node current = head;
        while (current != null) {
            System.out.println(current.data);
            current = current.next;
        }
    }

    public static void main(String[] args) {
        LinkedList linkedList = new LinkedList();
        linkedList.append(12);
        linkedList.append(12);
        linkedList.append(13);
        linkedList.append(13);
        linkedList.append(13);
        linkedList.append(13);
        linkedList.append(14);
        linkedList.append(14);
        linkedList.append(15);

        linkedList.deleteWithValue(14);
        linkedList.display();

        System.out.println("-----After Removal of Duplicates------");
        System.out.println(linkedList.removeDuplicates());

    }
}