Drag and Drop in a Tree

public class TreeDragDropTest {
    private static Display display;
    private static Shell shell;

    public static void main(String[] args) {
        display = new Display();
        shell = new Shell(display);
        shell.setLayout(new FillLayout());

        final Tree tree = createTree(shell);
        addDragDropSupport(tree);

        shell.setSize(400, 400);
        shell.open();
        while (!shell.isDisposed()) {
            if (!display.readAndDispatch())
                display.sleep();
        }
        display.dispose();
    }

    static void addDragDropSupport(final Tree tree) {
        //1) Define 'Transfer Type', 'Operation'
        Transfer[] types = new Transfer[] { TextTransfer.getInstance() };
        int operations = DND.DROP_MOVE | DND.DROP_COPY | DND.DROP_LINK;

        //2) DragSource
        final DragSource source = new DragSource(tree, operations);
        source.setTransfer(types);
        final TreeItem[] dragSourceItem = new TreeItem[1];
        source.addDragListener(new DragSourceListener() {
            public void dragStart(DragSourceEvent event) {
                TreeItem[] selection = tree.getSelection();
                //Selected a leaf node
                if (selection.length > 0 && selection[0].getItemCount() == 0) {
                    event.doit = true;
                    dragSourceItem[0] = selection[0];
                } else {
                    event.doit = false;
                }
            };

            public void dragSetData(DragSourceEvent event) {
                event.data = dragSourceItem[0].getText();
            }

            public void dragFinished(DragSourceEvent event) {
                if (event.detail == DND.DROP_MOVE)
                    dragSourceItem[0].dispose();
                dragSourceItem[0] = null;
            }
        });

        //3) DropTarget
        DropTarget target = new DropTarget(tree, operations);
        target.setTransfer(types);
        target.addDropListener(new DropTargetAdapter() {
            public void dragOver(DropTargetEvent event) {
                event.feedback = DND.FEEDBACK_EXPAND | DND.FEEDBACK_SCROLL;
                if (event.item != null) {
                    //Target TreeItem
                    TreeItem targetTreeItem = (TreeItem) event.item;

                    //Convert drop coordinate from Display to Tree
                    Point pt = display.map(null, tree, event.x, event.y);
                    Rectangle bounds = targetTreeItem.getBounds();
                    if (pt.y < bounds.y + bounds.height / 3) {
                        event.feedback |= DND.FEEDBACK_INSERT_BEFORE;
                    } else if (pt.y > bounds.y + 2 * bounds.height / 3) {
                        event.feedback |= DND.FEEDBACK_INSERT_AFTER;
                    } else {
                        event.feedback |= DND.FEEDBACK_SELECT;
                    }
                }
            }

            public void drop(DropTargetEvent event) {
                if (event.data == null) {
                    event.detail = DND.DROP_NONE;
                    return;
                }

                String text = (String) event.data;

                if (event.item == null) {
                    //Move to the root node
                    TreeItem item = new TreeItem(tree, SWT.NONE);
                    item.setText(text);
                } else {
                    //Move under a TreeItem node
                    TreeItem dropItem = (TreeItem) event.item;
                    Point pt = display.map(null, tree, event.x, event.y);

                    Rectangle bounds = dropItem.getBounds();
                    TreeItem parent = dropItem.getParentItem();

                    if (parent != null) {
                        //Target node has parent
                        TreeItem[] siblingItems = parent.getItems();

                        int index = 0;
                        for (int i = 0; i < siblingItems.length; i++) {
                            if (siblingItems[i] == dropItem) {
                                index = i;
                                break;
                            }
                        }

                        TreeItem newItem;
                        if (pt.y < bounds.y + bounds.height / 3)
                            newItem = new TreeItem(parent, SWT.NONE, index);
                        else if (pt.y > bounds.y + 2 * bounds.height / 3)
                            newItem = new TreeItem(parent, SWT.NONE, index + 1);
                        else
                            newItem = new TreeItem(dropItem, SWT.NONE);

                        newItem.setText(text);
                    } else {
                        //Target has no parent
                        TreeItem[] siblingItems = tree.getItems();

                        int index = 0;
                        for (int i = 0; i < siblingItems.length; i++) {
                            if (siblingItems[i] == dropItem) {
                                index = i;
                                break;
                            }
                        }

                        TreeItem newItem;
                        if (pt.y < bounds.y + bounds.height / 3)
                            newItem = new TreeItem(tree, SWT.NONE, index);
                        else if (pt.y > bounds.y + 2 * bounds.height / 3)
                            newItem = new TreeItem(tree, SWT.NONE, index + 1);
                        else
                            newItem = new TreeItem(dropItem, SWT.NONE);
                        newItem.setText(text);
                    }
                }
            }
        });
    }

    static Tree createTree(final Shell shell) {
        Tree tree = new Tree(shell, SWT.BORDER);
        for (int i = 0; i < 3; i++) {
            TreeItem item = new TreeItem(tree, SWT.NONE);
            item.setText("item " + i);
            for (int j = 0; j < 3; j++) {
                TreeItem subItem = new TreeItem(item, SWT.NONE);
                subItem.setText("item " + i + " " + j);
                for (int k = 0; k < 3; k++) {
                    TreeItem subsubItem = new TreeItem(subItem, SWT.NONE);
                    subsubItem.setText("item " + i + " " + j + " " + k);
                }
            }
        }

        return tree;
    }
}