JTree class.
*
* A JTree is a useful interface component for displaying
* hierarchical data. Like many other non-trivial Swing components,
* JTree doesn't contain any data; it simply
* provides a view of the data, presented as a tree. The data are
* held in a data model, which may be passed as an argument to
* the tree's constructor.
*
* The data are displayed vertically in rows. Each row is
* a node. The top row is the root node. Each
* JTree has precisely one root node, from which all other
* nodes descend. A node may or may not contain other nodes, called
* children. A node containing a child node is called
* a branch node. A node that does not contain a child node is
* called a leaf node.
* * In this demo, we display all the symbols that can be generated directly * from keys on a typical computer keyboard. The symbols are organized * hierarchically under the root node "Symbols" as three branch nodes * named "Letters", "Digits", and "Punctuation". Each branch node * has a set of leaf nodes containing the symbols for that branch.
*
* A key feature of JTree is the ability to collapse or expand
* branch nodes. When collapsed only the node is visible. When expanded,
* the child nodes are also visible. Our demo tree is pre-loaded into a
* JScrollPane component. Scrollbars automatically
* appear or disappear, as needed, as branch nodes are
* expanded or collapsed.
*
* It is possible it install a listener
* that detects the collapsing and expanding of branch nodes
* (TreeExpansionListener), however this is not
* demonstrated here.
*
* The most common listener for JTree is
* TreeSelectionListener, which generates an event
* each time a node is selected. The event triggers
* a call to the listener's valueChanged method, passing
* a TreeSelectionEvent object as an argument.
* Our extended JFrame
* class (the application window) implements
* TreeSelectionListener. In the valueChanged
* method we retrieve the node selected, and, if it is a leaf node,
* print its symbol on the console.
*
* Keyboard interaction.
* The following are the Microsoft
* windows-style actions supported for JTree:
* *
* JTree (Win32 L&F) * Navigate out forward | Tab * Navigate out backward | Shift+Tab * Expand entry | Right * Collapse entry | Left * Toggle expand/collapse for entry | Enter * Move up/down one entry | Up, Down * Move to first entry | Home * Move to last visible entry | End * Block move vertical | PgUp, PgDn * Block move left | Ctrl+PgUp * Block move right | Ctrl+PgDn * Block extend vertical | Shift+PgUp, Shift+PgDn * Select all | Ctrl+A * Select all | Ctrl+Slash * Deselect all | Ctrl+\ * Single select | Ctrl+Spacebar * Range-select | Shift+Spacebar * Extend selection up | Shift+Up * Extend selection down | Shift+Down * Extend selection to start of data | Shift+Home * Extend selection to end of data | Shift+End ** * For further details, consult the source code, * the
JTree API, and the Swing tutorial notes.
*
*
* Screen snap (launch)...
*
*
* Screen snap (with branch node expanded)...
*
* * @see source code * @author Scott MacKenzie, 2002 */ public class DemoTree { public static void main(String[] args) { // use look and feel for my system (Win32) try { UIManager.setLookAndFeel( UIManager.getSystemLookAndFeelClassName()); } catch (Exception e) {} DemoTreeFrame frame = new DemoTreeFrame(); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setTitle("DemoTree"); frame.pack(); frame.show(); } } class DemoTreeFrame extends JFrame implements TreeSelectionListener { private JTree t; public DemoTreeFrame() { final String[] CATEGORIES = { "Letters", "Digits", "Punctuation" }; final String[] SYMBOLS = { "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ", "0123456789", "~!@#$%^&*()_+`-={}|[]\\:\";'<>?,./" }; // ---------------------------------- // construct and configure components // ---------------------------------- DefaultMutableTreeNode top = new DefaultMutableTreeNode("Symbols"); DefaultMutableTreeNode node; Character nodeSymbol; for (int i = 0; i < CATEGORIES.length; ++i) { top.add(new DefaultMutableTreeNode(CATEGORIES[i])); for (int j = 0; j < SYMBOLS[i].length(); ++j) { node = (DefaultMutableTreeNode)(top.getChildAt(i)); nodeSymbol = new Character(SYMBOLS[i].charAt(j)); node.add(new DefaultMutableTreeNode(nodeSymbol)); } } // Create a JTree object, passing the data model as an argument // to the constructor. (Note: The data model is represented // by the node at the top of the tree hierarchy.) t = new JTree(top); // Set the selection mode to "single" (only one node can be // selected at a time). TreeSelectionModel tsm = t.getSelectionModel(); tsm.setSelectionMode(TreeSelectionModel.SINGLE_TREE_SELECTION); // put the tree in a scroll pane to facilitate viewing JScrollPane sp = new JScrollPane(t); sp.setPreferredSize(new Dimension(150, 250)); // ------------- // add listeners // ------------- t.addTreeSelectionListener(this); // ------------------ // arrange components // ------------------ JPanel p = new JPanel(); p.add(sp); p.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10)); this.setContentPane(p); } // -------------------------------------- // implement TreeSelectionListener method // -------------------------------------- public void valueChanged(TreeSelectionEvent tse) { // get the node that was selected DefaultMutableTreeNode node = (DefaultMutableTreeNode)t.getLastSelectedPathComponent(); // for this demo, we're only interested in leaf nodes if (!node.isLeaf()) return; // get the symbol associated with the node and print it Object o = node.getUserObject(); System.out.print(o); } }