Learning Java

Trees

One of Swing’s advanced components is JTree. Trees are good for representing hierarchical information, like the contents of a disk drive or a company’s organizational chart. As with all Swing components, the data model is distinct from the visual representation. This means you can do things like update the data model and trust that the visual component will be updated properly.

JTree is powerful and complex. It’s so complicated, in fact, that the classes that support JTree have their own package, javax.swing.tree . However, if you accept the defaults options for almost everything, JTree is very easy to use. Figure 15.6 shows a JTreerunning in a Swing application that we’ll describe a little later.

Figure 15-6. The JTree class in action

Nodes and Models

A tree’s data model is made up of interconnected nodes. A node has a name, typically, a parent, and some number of children (possibly 0). In Swing, a node is represented by the TreeNode interface. Nodes that can be modified are represented by MutableTreeNode. A concrete implementation of this interface is DefaultMutableTreeNode. One node, called the root node, usually resides at the top of the hierarchy.

A tree’s data model is represented by the TreeModel interface. Swing provides an implementation of this interface called DefaultTreeModel . You can create a DefaultTreeModel by passing a root TreeNode to its constructor.

You could ...