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/CheckboxTreeViewer.java
Item[] items = getChildren(item);
	if (items != null) {
		for (int i = 0; i < items.length; i++) {
			Item it = items[i];
			if (it.getData() != null && (it instanceof TreeItem)) {
				TreeItem treeItem = (TreeItem) it;
				treeItem.setChecked(state);
				setCheckedChildren(treeItem, state);
			}
		}
	}
}
/**
 * Sets which elements are checked in this viewer's tree.
 * The given list contains the elements that are to be checked;
 * all other elements are to be unchecked.
 * <p>
 * This method is typically used when restoring the interesting
 * state of a viewer captured by an earlier call to <code>getCheckedElements</code>.
 * </p>
 *
 * @param elements the array of checked elements
 * @see #getCheckedElements
 */
public void setCheckedElements(Object[] elements) {
	assertElementsNotNull(elements);
	Set checkedElements = new HashSet(elements.length*2+1);
	for (int i = 0; i < elements.length; ++i) {
		
		internalExpand(elements[i], false);