Advanced Swing Trees

Contents Introduction to Trees Simple Trees Editing Trees and Tree Paths Node Enumeration Rendering Nodes Listening to Tree Events

I. Introduction To Trees

Tree Terminology

Tree Traversal Orders

Java Tree Classes

II. Simple Trees To construct a JTree, supply the tree model in the constructor: TreeModel model = . . .; JTree tree = new JTree(model); How do you obtain a tree model? Creating a class that implements the TreeModel interface. Using the DefaultTreeModel that the Swing library supplies. To construct a default tree model, you must supply a root node. TreeNode root = . . .; DefaultTreeModel model = new DefaultTreeModel(root);

How do you obtain a tree node? Implement the TreeNode interface. Using the DefaultMutableTreeNode. This class implements the MutableTreeNode interface, a subinterface of TreeNode A default mutable tree node holds an object, the user object. The tree renders the user objects for all nodes. Unless you specify a renderer, the tree simply displays the string that is the result of the toString method.

Setting User Objects You can specify the user object in the constructor, DefaultMutableTreeNode node = new DefaultMutableTreeNode("Texas"); or you can set it later with the setUserObject method. . . . node.setUserObject("California");

Establishing the Parent/Child Relationships Start with the root node, and use the add method to add the children: DefaultMutableTreeNode root = new DefaultMutableTreeNode("World"); DefaultMutableTreeNode country = new DefaultMutableTreeNode("USA"); root.add(country); DefaultMutableTreeNode state = new DefaultMutableTreeNode("California"); country.add(state);

Constructing a JTree With a Root Node Construct a JTree with the tree model DefaultTreeModel treeModel = new DefaultTreeModel(root); JTree tree = new JTree(treeModel); Construct a JTree with a root node JTree tree = new JTree(root); Then the tree automatically constructs a default tree model.

III. Editing Trees and Tree Paths The JTree class has a way of identifying nodes in a tree. It does not deal with tree nodes, but with paths of objects, called tree paths. A tree path starts at the root and consists of a sequence of child nodes The TreePath class manages a sequence of Object (not TreeNode!) references.

Getting the Selected Node TreePath selectionPath = tree.getSelectionPath(); DefaultMutableTreeNode selectedNode = (DefaultMutableTreeNode) selectionPath.getLastPathComponent(); There is a convenience method that gives the selected node immediately: DefaultMutableTreeNode selectedNode = (DefaultMutableTreeNode) tree.getLastSelectedPathComponent();

Adding A New Node Insert a new node Remove a node void insertNodeInto(MutableTreeNode newChild, MutableTreeNode parent, int index) Remove a node void removeNodeFromParent(MutableTreeNode node) Notify the tree model listeners that node has changed void nodeChanged(TreeNode node)

Making a New Node Visible To expand all parent nodes so that the newly added node becomes visible TreeNode[] nodes = model.getPathToRoot(newNode); TreePath path = new TreePath(nodes); tree.makeVisible(path); To expand all nodes along the path, and scroll the node at the end of the path into view tree.scrollPathToVisible(path);

tree.setEditable(true); By default, tree nodes cannot be edited. To allow the user to edit a node tree.setEditable(true);

Editing a Tree

IV. Node Enumeration To find a node in a tree by starting at the root and visiting all children until you have found a match

Here is the typical usage pattern: Enumeration breadthFirst = node.breadthFirstEnumeration(); while (breadthFirst.hasMoreElements()) do something with breadthFirst.nextElement(); Enumeration breadthFirstEnumeration() Enumeration depthFirstEnumeration()

V. Rendering Nodes To change the way in which a tree component draws the nodes. All these changes are made possible by installing a new tree cell renderer into the tree. By default, the JTree class uses DefaultTreeCellRenderer objects to draw each node. The DefaultTreeCellRenderer class extends the JLabel class. The label contains the node icon and the node label.

You can customize the display in three ways. You can change the icons, font, and background color used by a DefaultTreeCellRenderer. These settings are used for all nodes in the tree. You can install a renderer that extends the DefaultTreeCellRenderer class and vary the icons, fonts, and background color for each node. You can install a renderer that implements the TreeCellRenderer interface, to draw a custom image for each node.

1. Using a DefaultTreeCellRenderer object DefaultTreeCellRenderer renderer = new DefaultTreeCellRenderer(); renderer.setLeafIcon(new ImageIcon( "blue-ball.gif")); // used for leaf nodes renderer.setClosedIcon(new ImageIcon( "red-ball.gif")); // used for collapsed nodes renderer.setOpenIcon(new ImageIcon( "yellow-ball.gif")); // used for expanded nodes tree.setCellRenderer(renderer);

2. Extending the DefaultTreeCellRenderer class class MyTreeCellRenderer extends DefaultTreeCellRenderer{ public Component getTreeCellRendererComponent( JTree tree, Object value, boolean selected, boolean expanded, boolean leaf, int row, boolean hasFocus){ super.getTreeCellRendererComponent(tree, value, selected, expanded, leaf, row, hasFocus); DefaultMutableTreeNode node = (DefaultMutableTreeNode) value; look at node.getUserObject(); Font font = appropriate font; setFont(font); return this; } };

V. Listening to Tree Events public TreeSelectionListener interface { void valueChanged(TreeSelectionEvent event) } That method is called whenever the user selects or deselects tree nodes. Adding a tree selection listener to a tree tree.addTreeSelectionListener(listener);

Tree Selection Modes The JTree class uses a TreeSelectionModel to manage node selection. TreeSelectionModel.SINGLE_TREE_SELECTION TreeSelectionModel.CONTIGUOUS_TREE_SELECTION TreeSelectionModel.DISCONTIGUOUS_TREE_SELECTION For example: tree.getSelectionModel().setSelectionMode( TreeSelectionModel.CONTIGUOUS_TREE_SELECTION);

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