Bug 141192 [Viewers] Javadoc change about multiple equal elements in StructuredViewer and AbstractTreeViewer
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/StructuredViewer.java
* resorting of the elements.
	 * 
	 * @param filter
	 *            a viewer filter
	 */
	public void addFilter(ViewerFilter filter) {
		if (filters == null) {
			filters = new ArrayList();
		}
		filters.add(filter);
		refresh();
	}
	/**
	 * Asserts that the given array of elements is itself non- <code>null</code>
	 * and contains no <code>null</code> elements.
	 * 
	 * @param elements
	 *            the array to check
	 */
	protected void assertElementsNotNull(Object[] elements) {
		Assert.isNotNull(elements);
		for (int i = 0, n = elements.length; i < n; ++i) {
			Assert.isNotNull(elements[i]);
		}
	}
	/**
	 * Associates the given element with the given widget. Sets the given item's
	 * data to be the element, and maps the element to the item in the element
	 * map (if enabled).
	 *