Bug 32254 [Viewers] AbstractTreeViewer uses HashSet to remember expansion state
I20030216 The custom hash table should be used instead. Otherwise expansion state may be lost due to a different equals implementation of the element and the IElementComparer.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/CheckboxTableViewer.java
boolean check = set.contains(element);
			
			if (item.getChecked() != check) {
				item.setChecked(check);
			}
		}
	}
}
/**
 * Sets the grayed state for the given element in this viewer.
 *
 * @param element the element
 * @param state <code>true</code> if the item should be grayed,
 *  and <code>false</code> if it should be ungrayed
 * @return <code>true</code> if the element is visible and the gray
 *  state could be set, and <code>false</code> otherwise
 */
public boolean setGrayed(Object element, boolean state) {
	Assert.isNotNull(element);
	Widget widget = findItem(element);
	if (widget instanceof TableItem) {
		((TableItem) widget).setGrayed(state);
		return true;
	}
	return false;
}
/**
 * Sets which nodes are grayed in this viewer.
 * The given list contains the elements that are to be grayed;
 * all other nodes are to be ungrayed.