Probleme pour creer un arbre en java

package trees;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;

import javax.swing.tree.MutableTreeNode;
import javax.swing.tree.TreeNode;

public class TreeNode_Impl implements MutableTreeNode {
	private ArrayList children;

	private MutableTreeNode parent;

	private Object userObject;

	public TreeNode_Impl() {
		this(null);
	}

	public TreeNode_Impl(Object userObject) {
		super();
		children = new ArrayList();
		this.userObject = userObject;
	}

	public void insert(MutableTreeNode child, int index) {
		if (index >= 0 && index < children.size()) {
			children.add(index, child);
		}
	}

	public void remove(int index) {
		MutableTreeNode node = (MutableTreeNode) children.remove(index);
		if (node != null) {
			node.setParent(null);
		}
	}

	public void remove(MutableTreeNode node) {
		if (children.contains(node)) {
			children.remove(node);
		}
	}

	public void setUserObject(Object object) {
		this.userObject = object;
	}

	public void removeFromParent() {
		parent.remove(this);
	}

	public void setParent(MutableTreeNode newParent) {
		this.parent = newParent;
		parent.insert(this, parent.getChildCount());
	}

	public TreeNode getChildAt(int childIndex) {
		return (TreeNode) children.get(childIndex);

	}

	public int getChildCount() {
		return children.size();
	}

	public TreeNode getParent() {
		return parent;
	}

	public int getIndex(TreeNode node) {
		if(!(children.contains(node)))
			return -1;
		return children.indexOf(node);
	}

	public boolean getAllowsChildren() {
		return false;
	}

	public boolean isLeaf() {
		return children.size()==0;
	}

	public Enumeration children() {
		return Collections.enumeration(children);
	}

	public Object getUserObject() {
		return userObject;
	}

}