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
Set checked = new HashSet(children.length);
	Set grayed = new HashSet(children.length);
	for (int i = 0; i < children.length; i++) {
		TableItem item = children[i];
		Object data = item.getData();
		if (data != null) {
			if (item.getChecked())
				checked.add(data);
			if (item.getGrayed())
				grayed.add(data);
		}
	}
	super.preservingSelection(updateCode);
	children = getTable().getItems();
	for (int i = 0; i < children.length; i++) {
		TableItem item = children[i];
		Object data = item.getData();
		if (data != null) {
			item.setChecked(checked.contains(data));
			item.setGrayed(grayed.contains(data));
		}
	}
}
/* (non-Javadoc)
 * Method declared on ICheckable.
 */
public void removeCheckStateListener(ICheckStateListener listener) {
	checkStateListeners.remove(listener);
}
/**