Bug 29711 Move refactoring doesn't honor read-only flags
Build I20030115 - JUnit setup - create TestCase.java in junit.runner - make it read-only - move TestCase from framework to runner - answer yes to override observe: the file in runner gets replaced althouh it is read-only
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/packageview/SelectionTransferDropAdapter.java
private static final int DROP_TIME_DIFF_TRESHOLD= 150;
	public SelectionTransferDropAdapter(StructuredViewer viewer) {
		super(viewer, DND.FEEDBACK_SCROLL | DND.FEEDBACK_EXPAND);
		fAddMethodStubAction= new AddMethodStubAction();
	}
	
	
	public Transfer getTransfer() {
		return LocalSelectionTransfer.getInstance();
	}
	
	
	public void dragEnter(DropTargetEvent event) {
		clear();
		super.dragEnter(event);
	}
	
	public void dragLeave(DropTargetEvent event) {
		clear();
		super.dragLeave(event);
	}
	
	private void clear() {
		fElements= null;
		fSelection= null;
		fMoveRefactoring= null;
		fCanMoveElements= 0;
		fCopyRefactoring= null;
		fCanCopyElements= 0;
	}