Exception occur when updateUI for JTree is triggered by KeyEvent

Name: wl91122 Date: 08/19/99


I have a problem with the updateUI() for a JTree when this is triggered from a KeyEvent.

To demonstrate the problem I reproduced it in a small example.
I expand the DymanicTree demo from the tutorial with a KeyListener, where
the updateUI() for the Tree is called. (DynamicTree.java)

Expand the parent node and then press F5-Key.
First time it works correct but from then on the following Exception occurs:

Exception occurred during event dispatching:
java.lang.NullPointerException
        at javax.swing.plaf.basic.BasicTreeUI$KeyHandler.keyPressed(Compiled Code)
        at javax.swing.plaf.basic.BasicTreeUI$KeyHandler.keyPressed(Compiled Code)
        at java.awt.AWTEventMulticaster.keyPressed(Compiled Code)
        at java.awt.Component.processKeyEvent(Compiled Code)
        at javax.swing.JComponent.processKeyEvent(Compiled Code)
        at java.awt.Component.processEvent(Compiled Code)
        at java.awt.Container.processEvent(Compiled Code)
        at java.awt.Component.dispatchEventImpl(Compiled Code)
        at java.awt.Container.dispatchEventImpl(Compiled Code)
        at java.awt.Component.dispatchEvent(Compiled Code)
        at java.awt.LightweightDispatcher.processKeyEvent(Compiled Code)
        at java.awt.LightweightDispatcher.dispatchEvent(Compiled Code)
        at java.awt.Container.dispatchEventImpl(Compiled Code)
        at java.awt.Window.dispatchEventImpl(Compiled Code)
        at java.awt.Component.dispatchEvent(Compiled Code)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:258)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:68)

The Example Code:
/** This code is based on an example provided by Richard Stanford,
 * a tutorial reader.
 */
import java.awt.*;
import javax.swing.*;
import javax.swing.tree.*;
import javax.swing.event.*;
import java.awt.event.*;

public class DynamicTree extends JPanel {
    protected DefaultMutableTreeNode rootNode;
    protected DefaultTreeModel treeModel;
    protected JTree tree;
    private Toolkit toolkit = Toolkit.getDefaultToolkit();

    public DynamicTree() {
        rootNode = new DefaultMutableTreeNode("Root Node");
        treeModel = new DefaultTreeModel(rootNode);

        tree = new JTree(treeModel);
        tree.setEditable(true);
        tree.getSelectionModel().setSelectionMode
                (TreeSelectionModel.SINGLE_TREE_SELECTION);
        tree.setShowsRootHandles(true);

        tree.addKeyListener(new KeyAdapter() {
            public void keyPressed(KeyEvent e) {
             if(e.getKeyCode() == KeyEvent.VK_F5) tree.updateUI();
            }
        });
        JScrollPane scrollPane = new JScrollPane(tree);
        setLayout(new GridLayout(1,0));
        add(scrollPane);
    }


    /** Remove all nodes except the root node. */
    public void clear() {
        rootNode.removeAllChildren();
        treeModel.reload();
    }

    /** Remove the currently selected node. */
    public void removeCurrentNode() {
        TreePath currentSelection = tree.getSelectionPath();
        if (currentSelection != null) {
            DefaultMutableTreeNode currentNode = (DefaultMutableTreeNode)
                         (currentSelection.getLastPathComponent());
            MutableTreeNode parent = (MutableTreeNode)(currentNode.getParent());
            if (parent != null) {
                treeModel.removeNodeFromParent(currentNode);
                return;
            }
        }

        // Either there was no selection, or the root was selected.
        toolkit.beep();
    }

    /** Add child to the currently selected node. */
    public DefaultMutableTreeNode addObject(Object child) {
        DefaultMutableTreeNode parentNode = null;
        TreePath parentPath = tree.getSelectionPath();

        if (parentPath == null) {
            parentNode = rootNode;
        } else {
            parentNode = (DefaultMutableTreeNode)
                         (parentPath.getLastPathComponent());
        }

        return addObject(parentNode, child, true);
    }

    public DefaultMutableTreeNode addObject(DefaultMutableTreeNode parent,
                                            Object child) {
        return addObject(parent, child, false);
    }

    public DefaultMutableTreeNode addObject(DefaultMutableTreeNode parent,
                                            Object child,
                                            boolean shouldBeVisible) {
        DefaultMutableTreeNode childNode =
                new DefaultMutableTreeNode(child);

        if (parent == null) {
            parent = rootNode;
        }

        treeModel.insertNodeInto(childNode, parent,
                                 parent.getChildCount());

        // Make sure the user can see the lovely new node.
        if (shouldBeVisible) {
            tree.expandPath(new TreePath(parent.getPath()));
            tree.scrollPathToVisible(new TreePath(childNode.getPath()));
        }
        return childNode;
    }
}

/*
 * This code is based on an example provided by Richard Stanford,
 * a tutorial reader.
 */
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.tree.*;

public class DynamicTreeDemo extends JPanel {
    private int newNodeSuffix = 1;

    public DynamicTreeDemo(JFrame frame) {
        //create the components
        final DynamicTree treePanel = new DynamicTree();
        populateTree(treePanel);

        JButton addButton = new JButton("Add");
        addButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                treePanel.addObject("New Node " + newNodeSuffix++);
            }
        });

        JButton removeButton = new JButton("Remove");
        removeButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                treePanel.removeCurrentNode();
            }
        });

        JButton clearButton = new JButton("Clear");
        clearButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                treePanel.clear();
            }
        });

        //Lay everything out.
        setLayout(new BorderLayout());
        treePanel.setPreferredSize(new Dimension(300, 150));
        add(treePanel, BorderLayout.CENTER);

        JPanel panel = new JPanel();
        panel.setLayout(new GridLayout(0,1));
        panel.add(addButton);
        panel.add(removeButton);
        panel.add(clearButton);
        add(panel, BorderLayout.EAST);
    }

    public void populateTree(DynamicTree treePanel) {
        String p1Name = new String("Parent 1");
        String p2Name = new String("Parent 2");
        String c1Name = new String("Child 1");
        String c2Name = new String("Child 2");

        DefaultMutableTreeNode p1, p2;

        p1 = treePanel.addObject(null, p1Name);
        p2 = treePanel.addObject(null, p2Name);

        treePanel.addObject(p1, c1Name);
        treePanel.addObject(p1, c2Name);

        treePanel.addObject(p2, c1Name);
        treePanel.addObject(p2, c2Name);
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("DynamicTreeDemo");

        Container contentPane = frame.getContentPane();
        contentPane.setLayout(new GridLayout(1,1));
        contentPane.add(new DynamicTreeDemo(frame));

        frame.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });

        frame.pack();
        frame.setVisible(true);
    }
}
(Review ID: 93715)
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