For a class assignment, we can't use any of the languages bultin types, so I'm stuck with my own list. Anyway, here's the situation:

public class CrazyStructure <T extends Comparable<? super T>> {
    MyLinkedList<MyTree<T>> trees; //error: type parameter MyTree is not within its bound
}

However:

public class CrazyStructure <T extends Comparable<? super T>> {
    LinkedList<MyTree<T>> trees;
}

Works. MyTree impleements the Comparable interface, but MyLinkedList doesn't. However, Java's LinkedList doesn't implement it either, according to this. So what's the problem and how do I fix it?

MyLinkedList:

public class MyLinkedList<T extends Comparable<? super T>> {
    private class Node<T> {
        private Node<T> next;
        private T data;

        protected Node();
        protected Node(final T value);
    }

    Node<T> firstNode;

    public MyLinkedList();
    public MyLinkedList(T value);

    //calls node1.value.compareTo(node2.value)
    private int compareElements(final Node<T> node1, final Node<T> node2);

    public void insert(T value);
    public void remove(T value);
}

MyTree:

public class LeftistTree<T extends Comparable<? super T>>
        implements Comparable {

    private class Node<T> {
        private Node<T> left, right;
        private T data;
        private int dist;

        protected Node();
        protected Node(final T value);
    }

    private Node<T> root;

    public LeftistTree();
    public LeftistTree(final T value);
    public Node getRoot();

    //calls node1.value.compareTo(node2.value)
    private int compareElements(final Node node1, final Node node2);

    private Node<T> merge(Node node1, Node node2);
    public void insert(final T value);
    public T extractMin();
    public int compareTo(final Object param);
}