TreeNode implements Iterable<TreeNode<T>>, Serializable, Cloneable { @SuppressWarnings("unchecked") public TreeNode<T> find(final T data) { if (isLeaf()) { return (data() == null ? data == null : data().equals(data)) ? this : null; } final TreeNode<T>[] searchedNode = (TreeNode<T>[]) Array.newInstance(getClass(), 1); traversePreOrder(new TraversalAction<TreeNode<T>>() { @Override public void perform(TreeNode<T> node) { if ((node.data() == null ? data == null : node.data().equals(data))) { searchedNode[0] = node; } } @Override public boolean isCompleted() { return searchedNode[0] != null; } }); return searchedNode[0]; } TreeNode(T data);  TreeNode(); abstract Collection<? extends TreeNode<T>> subtrees(); abstract boolean add(TreeNode<T> subtree); abstract boolean dropSubtree(TreeNode<T> subtree); abstract void clear(); abstract TreeNodeIterator iterator(); T data(); void setData(T data); boolean isRoot(); TreeNode<T> root(); TreeNode<T> parent(); boolean isLeaf(); @SuppressWarnings("unchecked") TreeNode<T> find(final T data); Collection<? extends TreeNode<T>> findAll(final T data); boolean hasSubtree(TreeNode<T> subtree); boolean contains(TreeNode<T> node); boolean containsAll(Collection<TreeNode<T>> nodes); boolean remove(TreeNode<T> node); boolean removeAll(Collection<TreeNode<T>> nodes); void traversePreOrder(TraversalAction<TreeNode<T>> action); void traversePostOrder(TraversalAction<TreeNode<T>> action); Collection<TreeNode<T>> preOrdered(); Collection<TreeNode<T>> postOrdered(); Collection<? extends TreeNode<T>> path(TreeNode<T> descendant); TreeNode<T> commonAncestor(TreeNode<T> node); boolean isSiblingOf(TreeNode<T> node); boolean isAncestorOf(TreeNode<T> node); boolean isDescendantOf(TreeNode<T> node); long size(); int height(); int level(); @SuppressWarnings("unchecked") @Override TreeNode<T> clone(); @SuppressWarnings("unchecked") @Override boolean equals(Object obj); @Override int hashCode(); @Override String toString();  }
@Test public void testFind() { String messageTreeNodeFoundExpected = "The tree expected to have the searched data, but actually was not"; assertEquals(messageTreeNodeFoundExpected, node6, node6.find(NODE_DATA_4)); assertEquals(messageTreeNodeFoundExpected, node7, node2.find(null)); assertEquals(messageTreeNodeFoundExpected, node7, node7.find(null)); assertEquals(messageTreeNodeFoundExpected, node5, node3.find(NODE_DATA_1)); assertEquals(messageTreeNodeFoundExpected, node4, root.find(NODE_DATA_4)); String messageTreeNodeNotFoundExpected = "The tree with the searched data was not expected to be found, but actually was"; assertNull(messageTreeNodeNotFoundExpected, node6.find("data")); assertNull(messageTreeNodeNotFoundExpected, root.find("data")); }