Trees - The Definitive Guide to Java Swing - page 654

Querying Node Relationships
The DefaultMutableTreeNode class provides several ways to determine the relationship between
two nodes. In addition, you can check to see if two nodes share a common parent using the
following methods:

• isNodeAncestor(TreeNode aNode) : Returns true if aNode is the current node or a parent of
the current node. This recursively checks getParent() until aNode or null is found.

• isNodeChild(TreeNode aNode) : Returns true if the current node is the parent of aNode .

• isNodeDescendant(DefaultMutableTreeNode aNode) : Returns true if the current node is
aNode or an ancestor of aNode .

• isNodeRelated(DefaultMutableTreeNode aNode) : Returns true if both the current node
and aNode share the same root (are in the same tree).

• isNodeSibling(TreeNode aNode) : Returns true if both nodes share the same parent.

Each method returns a boolean value, indicating whether or not the relationship exists.
If two nodes are related, you can ask for the root of the tree to find a shared ancestor.
However, this ancestor might not be the closest ancestor within the tree. If a common
node exists lower down in the tree, you can use the public TreeNode getSharedAncestor
(DefaultMutableTreeNode aNode) method to find this closer ancestor. If none exists because
the two nodes aren't in the same tree, null is returned.

■ Note If a node asks for the shared ancestor of that node and itself, the shared ancestor is the node itself.

In other words, a node's closest ancestor to itself is itself.

Traversing Trees
The TreeNode interface and DefaultMutableTreeNode class provide several means of traveling to
all the nodes below a specific node. Given a specific TreeNode , you can walk to each descendant
node by going through the children() of each node, including the initial node. Given a specific
DefaultMutableTreeNode , you can find all the descendants by following both getNextNode()
and getPreviousNode() methods until no additional nodes are found. The following code frag-
ment demonstrates the use of the children() method of TreeNode to traverse an entire tree,
given a starting node.

public void printDescendants(TreeNode root) {
System.out.println(root);
Enumeration children = root.children();
if (children != null) {
while(children.hasMoreElements()) {
printDescendants((TreeNode)children.nextElement());
}
}
}