Trees - The Definitive Guide to Java Swing - page 651

instead of the first, requires you to ask the node with getChildCount() how many children it
already has and then add 1:
mutableTreeNode.insert(childMutableTreeNode, mutableTreeNode.getChildCount()+1);
At least for the DefaultMutableTreeNode class described next, setParent() sets a node to be
the parent of a child node, even though it doesn't make the child node a child of the parent. In
other words, don't call setParent() yourself; call insert() , and it will set the parent accordingly.
■ Caution The insert() method doesn't allow circular ancestry, where the child node to be added is an
ancestor to the parent. If that's attempted, an IllegalArgumentException will be thrown.
DefaultMutableTreeNode Class
The DefaultMutableTreeNode class provides an implementation of the MutableTreeNode interface
(which implements the TreeNode interface). When you're creating a tree from a Hashtable , an
array, or a Vector constructor, JTree automatically creates the nodes as a set of type
DefaultMutableTreeNode . If, on the other hand, you want to create the nodes yourself, you need
to create one instance of type DefaultMutableTreeNode for every node in your tree.
Creating a DefaultMutableTreeNode
Three constructors are available for creating instances of DefaultMutableTreeNode :
public DefaultMutableTreeNode()
DefaultMutableTreeNode node = new DefaultMutableTreeNode();
public DefaultMutableTreeNode(Object userObject)
DefaultMutableTreeNode node = new DefaultMutableTreeNode("Node");
public DefaultMutableTreeNode(Object userObject, boolean allowsChildren)
DefaultMutableTreeNode node = new DefaultMutableTreeNode("Node", false);
The information stored at every node is called the user object . When not specified by one
of the constructors, this user object is null . In addition, you can specify whether a node is
allowed to have children.
Building DefaultMutableTreeNode Hierarchies
Building a hierarchy of nodes of type DefaultMutableTreeNode requires creating an instance
of type DefaultMutableTreeNode , creating nodes for its children, and then connecting them.
Before using DefaultMutableTreeNode directly to create the hierarchy, first let's see how to use
the new NamedVector class to create a tree with four nodes: one root and three leaf nodes.
Vector vector = new NamedVector("Root", new String[]{ "Mercury", "Venus", "Mars"} );
JTree tree = new JTree(vector);