Bug 263845 [CommonNavigator] Drag/drop folder from non-Java Proj to Java Proj does copy instead of move sometimes
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ViewerDropAdapter.java
import org.eclipse.swt.dnd.TransferData;
import org.eclipse.swt.graphics.Point;
import org.eclipse.swt.graphics.Rectangle;
import org.eclipse.swt.widgets.Item;
import org.eclipse.swt.widgets.TableItem;
import org.eclipse.swt.widgets.TreeItem;
/**
 * This adapter class provides generic drag-and-drop support for a viewer.
 * <p>
 * Subclasses must implement the following methods:
 * <ul>
 *   <li><code>validateDrop</code> - identifies valid drop targets in viewer</li>
 *   <li><code>performDrop</code> - carries out a drop into a viewer</li>
 * </ul>
 * The <code>setFeedbackEnabled</code> method can be called to turn on and off 
 * visual insertion feedback (on by default).
 * </p>
 */
public abstract class ViewerDropAdapter extends DropTargetAdapter {
    /**
     * Constant describing the position of the cursor relative 
     * to the target object.  This means the mouse is positioned
     * slightly before the target.
     * @see #getCurrentLocation()
     */
    public static final int LOCATION_BEFORE = 1;
    /**
     * Constant describing the position of the cursor relative 
     * to the target object.  This means the mouse is positioned
     * slightly after the target.