How to make JTree cell renderer respect layout?

Question

Hi,
In the JTree tutorial, the first example TreeDemo shows a simple tree.
http://java.sun.com/docs/books/tutorial/uiswing/components/tree.html
If you grab the frame and make it really thin, you get a horizontal scroll bar in the top pane.
How can I make it so that the tree cells just draw "..." at the end of the string if there is not enough space?
I know the tree cell renderer uses JLabel, but they never seem to show "...", which is one of the best features of a JLabel. Any help is greatly appreciated!

Answer 1

Hi,
I got it working, but I also discovered a Java bug that ruins all this effort!
Calculating the node's position & width:
- When child nodes are indented, there is an "L" shaped line drawn... the space to the left of the line's vertical bar is the "leftChildIndent", and the space to the right is the "rightChildIndent". So you add both to get the whole indent.
- I use label.getPreferredSize().width to figure out the node width, since that includes the icon width, the icon-text gap, and the font metrics.
Example program:
- This program models how I want it to look... Always expanded and automatic "..." when the scroll pane is not big enough.
Bug found:
- There is a runnable example below. Just run it and after a couple seconds, move the split pane to the right.
- I use a timer to add a new node every 1 second. The new nodes get stuck being too small, and the original nodes don't have this problem.
// =====================================================
* Adaptation of TreeDemo to allow for tree nodes that show "..."
* when there is not enough space to display the whole label.
import java.awt.Component;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JSplitPane;
import javax.swing.JTree;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.event.TreeExpansionEvent;
import javax.swing.event.TreeWillExpandListener;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeCellRenderer;
import javax.swing.tree.DefaultTreeModel;
import javax.swing.tree.ExpandVetoException;
import javax.swing.tree.TreeCellRenderer;
import javax.swing.tree.TreeSelectionModel;
public class TreeDemo extends JPanel {
    private JTree tree;
    protected class EllipsesTreeCellRenderer implements TreeCellRenderer {
        Integer leftIndent = (Integer) UIManager.get("Tree.leftChildIndent");
        Integer rightIndent = (Integer) UIManager.get("Tree.rightChildIndent");
        int indent = leftIndent.intValue() + rightIndent.intValue();
        JLabel label = new JLabel();
        DefaultTreeCellRenderer r = new DefaultTreeCellRenderer();
        public Component getTreeCellRendererComponent(JTree tree, Object value,
                boolean selected, boolean expanded, boolean leaf, int row,
                boolean hasFocus) {
            label.setText("why hello there why hello there why hello there");
            if (selected) {
                label.setForeground(r.getTextSelectionColor());
                label.setBackground(r.getBackgroundSelectionColor());
            } else {
                label.setForeground(r.getTextNonSelectionColor());
                label.setBackground(r.getBackgroundNonSelectionColor());
            if (leaf) {
                label.setIcon(r.getLeafIcon());
            } else if (expanded) {
                label.setIcon(r.getOpenIcon());
            } else {
                label.setIcon(r.getClosedIcon());
            label.setComponentOrientation(tree.getComponentOrientation());
            int labelWidth = label.getPreferredSize().width;
            DefaultMutableTreeNode node = (DefaultMutableTreeNode) value;
            int level = node.getLevel();
            if (!tree.isRootVisible()) {
                --level;
            int indentWidth = indent * level;
            int rendererWidth = labelWidth + indentWidth;
            // This is zero the first few times getTreeCellRenderer is called
            // because the tree is not yet visible.
            int maxWidth = (int) tree.getVisibleRect().getWidth();
            if (maxWidth > 0) {
                if (rendererWidth > maxWidth) {
                    // figure out how much space "..." will consume.
                    label.setText(label.getText() + "...");
                    maxWidth = maxWidth
                            - (label.getPreferredSize().width - labelWidth);
                    label.setText(label.getText());
                    // chop off characters until "..." fits in the visible
                    // portion.
                    if (maxWidth > 0) {
                        while (rendererWidth > maxWidth
                                && label.getText().length() > 1) {
                            label.setText(label.getText().substring(0,
                                    label.getText().length() - 2));
                            rendererWidth = indentWidth
                                    + label.getPreferredSize().width;
                        label.setText(label.getText() + "...");
            return label;
    public TreeDemo() {
        super(new GridLayout(1, 0));
        //Create the nodes.
        final DefaultMutableTreeNode top = new DefaultMutableTreeNode("");
        createNodes(top);
        //Create a tree that allows one selection at a time.
        tree = new JTree(top);
        tree.getSelectionModel().setSelectionMode(
                TreeSelectionModel.SINGLE_TREE_SELECTION);
        tree.setCellRenderer(new EllipsesTreeCellRenderer());
        tree.addTreeWillExpandListener(new TreeWillExpandListener() {
            public void treeWillExpand(TreeExpansionEvent event) {
            public void treeWillCollapse(TreeExpansionEvent event)
                    throws ExpandVetoException {
                throw new ExpandVetoException(event);
        for (int i = tree.getRowCount(); i >= 0; i--) {
            tree.expandRow(i);
        //Create the scroll pane and add the tree to it.
        JScrollPane treeView = new JScrollPane(tree);
        //Add the scroll panes to a split pane.
        JSplitPane splitPane = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT);
        splitPane.setTopComponent(treeView);
        splitPane.setBottomComponent(new JLabel(""));
        Dimension minimumSize = new Dimension(0, 0);
        treeView.setMinimumSize(minimumSize);
        splitPane.setDividerLocation(200); //XXX: ignored in some releases
        //of Swing. bug 4101306
        //workaround for bug 4101306:
        //treeView.setPreferredSize(new Dimension(100, 100));
        // Makes tree nodes appear cut-off initially.
        splitPane.setPreferredSize(new Dimension(500, 300));
        //Add the split pane to this panel.
        add(splitPane);
        // Adds a new node every 1 second
        Timer timer = new Timer(1000, new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                DefaultTreeModel model = (DefaultTreeModel) tree.getModel();
                DefaultMutableTreeNode child = new DefaultMutableTreeNode("");
                model.insertNodeInto(child, top, 0);
                for (int i = tree.getRowCount(); i >= 0; i--) {
                    tree.expandRow(i);
        timer.start();
    private void createNodes(DefaultMutableTreeNode top) {
        DefaultMutableTreeNode category = null;
        DefaultMutableTreeNode book = null;
        category = new DefaultMutableTreeNode("");
        top.add(category);
        category.add(new DefaultMutableTreeNode(""));
        category.add(new DefaultMutableTreeNode(""));
        category.add(new DefaultMutableTreeNode(""));
        category.add(new DefaultMutableTreeNode(""));
        category.add(new DefaultMutableTreeNode(""));
        category.add(new DefaultMutableTreeNode(""));
        category.add(new DefaultMutableTreeNode(""));
        category.add(new DefaultMutableTreeNode(""));
        category.add(new DefaultMutableTreeNode(""));
     * Create the GUI and show it. For thread safety, this method should be
     * invoked from the event-dispatching thread.
    private static void createAndShowGUI() {
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (Exception e) {
            System.err.println("Couldn't use system look and feel.");
        //Make sure we have nice window decorations.
        JFrame.setDefaultLookAndFeelDecorated(true);
        //Create and set up the window.
        JFrame frame = new JFrame("TreeDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        //Create and set up the content pane.
        TreeDemo newContentPane = new TreeDemo();
        newContentPane.setOpaque(true); //content panes must be opaque
        frame.setContentPane(newContentPane);
        //Display the window.
        frame.pack();
        frame.setVisible(true);
    public static void main(String[] args) {
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
}