Bug 258736 [Viewers] [JFace] setUseHashLookUp() and multiple occurrences of same domain object in TreeViewer
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/TreeViewer.java
if ((getTree().getStyle() & SWT.VIRTUAL) != 0) {
			
			
			if (item.getData(VIRTUAL_DISPOSE_KEY) == null) {
				item.setData(VIRTUAL_DISPOSE_KEY, Boolean.TRUE);
				item.addDisposeListener(new DisposeListener() {
					public void widgetDisposed(DisposeEvent e) {
						if (!treeIsDisposed) {
							Object data = item.getData();
							if (usingElementMap() && data != null) {
								unmapElement(data, item);
							}
						}
					}
				});
			}
		}
	}
	/*
	 * (non-Javadoc)
	 *
	 * @see org.eclipse.jface.viewers.ColumnViewer#getRowPartFromItem(org.eclipse.swt.widgets.Widget)
	 */
	protected ViewerRow getViewerRowFromItem(Widget item) {
		if( cachedRow == null ) {
			cachedRow = new TreeViewerRow((TreeItem) item);
		} else {
			cachedRow.setItem((TreeItem) item);
		}
		return cachedRow;