Java Doubly Linked List
Can use Generics for Node to provide something for more then just ints.

class Node&lt;T&gt; {
    Node prev;
    Node next;
    T data;

    public Node(T data) {
        this.data = data;
        prev = null;
        next = null;
    }
}


then same for your linked list implementation.  

class LinkedList&lt;T&gt; {
    Node&lt;T&gt; head;

    ...

    public void insert(T d) {
        if (head == null) {
            head = new Node&lt;T&gt;(d);
            return;
        }

    ...


Can make T extends Comparable and use comparable interface to compare if they are less/greater than