/** * @return true if the child map contains this key OR the parent map is not null and contains this key. * <pre>child.containsKey(key) || (parent != null && parent.containsKey(key));</pre> */ public boolean containsKey(Object key) { if (key == null) throw new NullPointerException("Null keys forbidden!"); return child.containsKey(key) || (parent != null && parent.containsKey(key)); }