Autoscroll behavior during DnD in JTree, 1.4 vs 1.6

Question

The following code compiles under both Java 1.4 and Java 1.6. I'm wondering if anyone knows why the following actions cause different behaviors between the two versions:
1. When the frame opens, you should see a fully-expanded tree (which, because of the small size, causes a vertical scrollbar to appear).
2. Make a drag-and-drop gesture on the first child node ("blue"), and attempt to cause the tree to scroll down so you can drop it on the last parent node ("food").
Under 1.6, the tree scrolls nicely as you hold the DnD gesture.
Under 1.4, the tree does not scroll. I had some hope JTree.setAutoscrolls(true) would help, but it did not.
Any suggestions how to get 1.4 to behave the way 1.6 does?
Thanks for your time.
import javax.swing.*;
import javax.swing.tree.DefaultTreeModel;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.TreePath;
import javax.swing.tree.TreeNode;
import java.awt.*;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.io.IOException;
import java.util.Enumeration;
public class AutoScroll14 extends JFrame {
    public static void main(String[] args) {
        new AutoScroll14();
    public AutoScroll14() throws HeadlessException {
        super("AutoScroll 1.4");
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        JTree tree = new JTree();
        tree.setDragEnabled(true);
        tree.setTransferHandler(new MyTransferHandler());
        expand(tree, tree.getPathForRow(0));
        JScrollPane sp = new JScrollPane(tree);
        sp.setPreferredSize(new Dimension(300, 200));
        Container content = getContentPane();
        content.setLayout(new BorderLayout());
        content.add(sp, BorderLayout.CENTER);
        pack();
        setVisible(true);
    private void expand(JTree tree, TreePath path) {
        TreeNode node = (TreeNode) path.getLastPathComponent();
        for (Enumeration e = node.children(); e.hasMoreElements();) {
            TreeNode n = (TreeNode) e.nextElement();
            TreePath newPath = path.pathByAddingChild(n);
            expand(tree, newPath);
        tree.expandPath(path);
    private class MyTransferHandler extends TransferHandler {
        private DataFlavor localStringFlavor;
        private String localStringType = DataFlavor.javaJVMLocalObjectMimeType + ";class=java.lang.String";
        private MyTransferHandler() {
            try {
                localStringFlavor = new DataFlavor(localStringType);
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
        public boolean importData(JComponent comp, Transferable t) {
            if (!canImport(comp, t.getTransferDataFlavors())) {
                return false;
            String data = null;
            try {
                if (hasLocalStringFlavor(t.getTransferDataFlavors())) {
                    data = (String) t.getTransferData(localStringFlavor);
                } else {
                    return false;
            } catch (UnsupportedFlavorException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            String location = null;
            if (comp instanceof JTree) {
                location = ((JTree) comp).getSelectionPath().toString();
            System.out.println("Dropping [" + data + "] on location [" + location + "]");
            return true;
        private boolean hasLocalStringFlavor(DataFlavor[] flavors) {
            if (localStringFlavor == null) {
                return false;
            for (int i = 0; i < flavors.length; i++) {
                if (flavors.equals(localStringFlavor)) {
return true;
return false;
public boolean canImport(JComponent comp, DataFlavor[] flavors) {
return hasLocalStringFlavor(flavors);
protected Transferable createTransferable(JComponent c) {
if (c instanceof JTree) {
String toTransfer = ((JTree) c).getSelectionPath().toString();
System.out.println("Creating transferable [" + toTransfer + "]");
return new StringTransferable(toTransfer);
System.out.println("Could not create transferable");
return null;
public int getSourceActions(JComponent c) {
return COPY_OR_MOVE;
private class StringTransferable implements Transferable {
private String data;
private StringTransferable(String data) {
this.data = data;
public DataFlavor[] getTransferDataFlavors() {
return new DataFlavor[] { localStringFlavor };
public boolean isDataFlavorSupported(DataFlavor flavor) {
return localStringFlavor.equals(flavor);
public Object getTransferData(DataFlavor flavor) throws UnsupportedFlavorException, IOException {
if (!isDataFlavorSupported(flavor)) {
throw new UnsupportedFlavorException(flavor);
return data;

Answer 1

I added the class "TreeDropTarget".
"TreeDropTarget" extends the class "DropTarget", which implements the interface "DropTargetListener".
DropTargetListener has a few methods, that are called automatically by Swing during drag operation
(dragOver, dragExit, drop). So we can implement "autoscroll", as well as "automatic node expansion".
With "automatic node expansion", a collapsed node will be expanded,
so that its children become visible and we can do a drop on them:
package demo;
* AutoScroll.java
* source level 1.4
import javax.swing.*;
import javax.swing.tree.*;
import java.awt.*;
import java.awt.datatransfer.*;
import java.awt.dnd.*;
import java.io.*;
import java.util.*;
public class AutoScroll extends JFrame {
    public static void main(String[] args) {
        new AutoScroll();
    public AutoScroll() throws HeadlessException {
        super("AutoScroll " + System.getProperty("java.version"));
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        JTree tree = new JTree();
        tree.setDragEnabled(true);
        tree.setTransferHandler(new MyTransferHandler());
        tree.setDropTarget(new TreeDropTarget());//<----------------------
        expand(tree, tree.getPathForRow(0));
        JScrollPane sp = new JScrollPane(tree);
        sp.setPreferredSize(new Dimension(300, 200));
        Container content = getContentPane();
        content.setLayout(new BorderLayout());
        content.add(sp, BorderLayout.CENTER);
        pack();
        setVisible(true);
    private void expand(JTree tree, TreePath path) {
        TreeNode node = (TreeNode) path.getLastPathComponent();
        for (Enumeration e = node.children(); e.hasMoreElements();) {
            TreeNode n = (TreeNode) e.nextElement();
            TreePath newPath = path.pathByAddingChild(n);
            expand(tree, newPath);
        tree.expandPath(path);
    private class MyTransferHandler extends TransferHandler {
        private DataFlavor localStringFlavor;
        private String localStringType = DataFlavor.javaJVMLocalObjectMimeType + ";class=java.lang.String";
        private AutoScroll.MyTransferHandler.StringTransferable transferable;
        private MyTransferHandler() {
            try {
                localStringFlavor = new DataFlavor(localStringType);
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
        protected void exportDone(JComponent comp, Transferable t, int action) {
            if (t == null) {
                t = transferable;
            if (!canImport(comp, t.getTransferDataFlavors())) {
                return;
            String data = null;
            try {
                if (hasLocalStringFlavor(t.getTransferDataFlavors())) {
                    data = (String) t.getTransferData(localStringFlavor);
                } else {
                    return;
            } catch (UnsupportedFlavorException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            String location = null;
            if (comp instanceof JTree) {
                location = ((JTree) comp).getSelectionPath().toString();
            System.out.println("Dropping [" + data + "] on location [" + location + "]");
            return;
        private boolean hasLocalStringFlavor(DataFlavor[] flavors) {
            if (localStringFlavor == null) {
                return false;
            for (int i = 0; i < flavors.length; i++) {
                if (flavors.equals(localStringFlavor)) {
return true;
return false;
public boolean canImport(JComponent comp, DataFlavor[] flavors) {
return hasLocalStringFlavor(flavors);
protected Transferable createTransferable(JComponent c) {
if (c instanceof JTree) {
String toTransfer = ((JTree) c).getSelectionPath().toString();
System.out.println("Creating transferable [" + toTransfer + "]");
transferable = new StringTransferable(toTransfer);
return transferable;
System.out.println("Could not create transferable");
return null;
public int getSourceActions(JComponent c) {
return COPY_OR_MOVE;
private class StringTransferable implements Transferable {
private String data;
private StringTransferable(String data) {
this.data = data;
public DataFlavor[] getTransferDataFlavors() {
return new DataFlavor[]{localStringFlavor};
public boolean isDataFlavorSupported(DataFlavor flavor) {
return localStringFlavor.equals(flavor);
public Object getTransferData(DataFlavor flavor) throws UnsupportedFlavorException, IOException {
if (!isDataFlavorSupported(flavor)) {
throw new UnsupportedFlavorException(flavor);
return data;
class TreeDropTarget extends DropTarget {
public TreeDropTarget() {
super();
public void dragOver(DropTargetDragEvent dtde) {
JTree tree = (JTree) dtde.getDropTargetContext().getComponent();
Point loc = dtde.getLocation();
updateDragMark(tree, loc);
autoscroll(tree, loc);
super.dragOver(dtde);
private Insets getAutoscrollInsets() {
return autoscrollInsets;
private void autoscroll(JTree tree, Point cursorLocation) {
Insets insets = getAutoscrollInsets();
Rectangle outer = tree.getVisibleRect();
Rectangle inner = new Rectangle(
outer.x + insets.left,
outer.y + insets.top,
outer.width - (insets.left + insets.right),
outer.height - (insets.top + insets.bottom));
if (!inner.contains(cursorLocation)) {
Rectangle scrollRect = new Rectangle(
cursorLocation.x - insets.left,
cursorLocation.y - insets.top,
insets.left + insets.right,
insets.top + insets.bottom);
tree.scrollRectToVisible(scrollRect);
public void updateDragMark(JTree tree, Point location) {
int row = tree.getRowForPath(tree.getClosestPathForLocation(location.x, location.y));
TreePath path = tree.getPathForRow(row);
if (path != null) {
markNode(tree, location);
private void markNode(JTree tree, Point location) {
TreePath path = tree.getClosestPathForLocation(location.x, location.y);
if (path != null) {
if (lastRowBounds != null) {
Graphics g = tree.getGraphics();
g.setColor(Color.white);
g.drawLine(lastRowBounds.x, lastRowBounds.y,
lastRowBounds.x + lastRowBounds.width, lastRowBounds.y);
tree.setSelectionPath(path);
tree.expandPath(path);
private Rectangle lastRowBounds;
private Insets autoscrollInsets = new Insets(20, 20, 20, 20);