Bug 126658 [CommonNavigator] [DND] Complete definition of DND API
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/navigator/CommonDropAdapterAssistant.java
protected void doInit() {
	}
	/**
	 * Validates dropping on the given object. This method is called whenever
	 * some aspect of the drop operation changes.
	 * <p>
	 * Subclasses must implement this method to define which drops make sense.
	 * If clients return true, then they will be allowed to handle the drop in
	 * {@link #handleDrop(DropTargetEvent, Object) }.
	 * </p>
	 * 
	 * @param target
	 *            the object that the mouse is currently hovering over, or
	 *            <code>null</code> if the mouse is hovering over empty space
	 * @param operation
	 *            the current drag operation (copy, move, etc.)
	 * @param transferType
	 *            the current transfer type
	 * @return <code>true</code> if the drop is valid, and <code>false</code>
	 *         otherwise
	 */
	public abstract boolean validateDrop(Object target, int operation,
			TransferData transferType);
	/**
	 * Carry out the DND operation
	 * 
	 * @param aDropTargetEvent
	 *            The drop target event.
	 * @param aTarget
	 *            The object being dragged onto