XML Tree structure

Question

Hi there,
I am in a datastructures class and we're supposed to create classes to represent an XML hierarchy in java. There is a base class that is inherited by the different node types (Document, Element, Text). Unfortunately I am running into an issue of keeping track of the parent nodes. Normally I would just create a method called setParent(Node parentNode) when addChild(Node childNode) is called. I can't do that because of how they defined the interface. Because the Node interface doesn't include that method declaration... it isn't accessible, so I'd have to cast it to the type of the base class with the setParent(Node parentNode) method. This increases the likelihood that the code would fail if a node interface type that isn't my implementation is passed into setParent().
I can't modify their interface so I am not sure what else I can do to track the parent classes. Any ideas?
P.S. They are using checkstyle which won't let you use public or protected properties.

Answer 1

Ok, sorry I should have put the interface on here:
public interface Node {
    int DOCUMENT_NODE = 1;
    int ELEMENT_NODE = 2;
    int TEXT_NODE = 3;
     * @return the type of this node (DOCUMENT_NODE, ELEMENT_NODE, or TEXT_NODE)
    int getType();
     * @return the parent node of this node, or null if it has no parent
    Node getParent();
     * @return the first child of this node, or null if it has no children
    Node getFirstChild();
     * @return the last child of this node, or null if it has no children
    Node getLastChild();
     * @return the next sibling of this node, or null if it has no next sibling
    Node getNextSibling();
     * @return the previous sibling of this node, or null if it has no previous sibling
    Node getPreviousSibling();
     * Inserts a new child node under the target node.
     * @param newChild the new child node to be inserted
     * @param child the child node before which the new node should be inserted
     * @throws IllegalArgumentException if newChild is null
     * @throws IllegalArgumentException if child is null
     * @throws IllegalArgumentException if child is not a child of the target node
    void insertChildBefore(Node newChild, Node child);
     * Appends a child to the target node's list of children.
     * @param newChild the new child node to be appended
     * @throws IllegalArgumentException if newChild is null
    void appendChild(Node newChild);
     * Removes a child from the target node's list of children.
     * @param child the child to be removed
     * @throws IllegalArgumentException if child is null
     * @throws IllegalArgumentException if child is not a child of the target node
    void removeChild(Node child);
     * Replaces an existing child node with a new node.
     * @param newChild the new node that is replacing the old node
     * @param oldChild the old node that is being replaced
     * @throws IllegalArgumentException if newChild is null
     * @throws IllegalArgumentException if oldChild is null
     * @throws IllegalArgumentException if oldChild is not a child of the target node
    void replaceChild(Node newChild, Node oldChild);
}