JTree

JTree is a Swing component used to display hierarchical data in a tree structure. It is part of the Java Swing library (javax.swing) and renders a tree of nodes that can be expanded or collapsed by the user. The visual representation is provided by a TreeCellRenderer, while the underlying data is supplied by a TreeModel.

Data model and nodes: The TreeModel defines the root and the child relationships between nodes. Nodes are typically instances of TreeNode; a common mutable implementation is DefaultMutableTreeNode, and the standard model is DefaultTreeModel. Developers construct trees by composing DefaultMutableTreeNode objects and attaching them to a root node. The model fires events to update the UI when the structure changes.

Rendering, editing, and selection: JTree uses a TreeCellRenderer to render each node. The default renderer (DefaultTreeCellRenderer) shows icons for open, closed, and leaf nodes. JTree can be made editable with setEditable(true), enabling in-place renaming via a TreeCellEditor. Selection is controlled by a TreeSelectionModel, with modes such as SINGLE_TREE_SELECTION, CONTIGUOUS_TREE_SELECTION, and DISCONTIGUOUS_TREE_SELECTION. Listeners such as TreeSelectionListener and TreeExpansionListener respond to user actions.

Interaction and integration: The component is typically placed inside a JScrollPane for scrolling. It supports keyboard navigation, drag and drop, and accessibility features. Custom behavior is achieved through custom renderers, editors, or a custom TreeModel to represent the data.

Usage notes and limitations: For very large trees, performance can deteriorate; Swing does not provide virtualization. Changes to the tree should be performed on the Event Dispatch Thread. Providing a responsive tree often involves a well-constructed model and, if needed, background loading for large data sets.