code: public static String getSimpleName(Element element) {
  		if (element.getKind() != ElementKind.CLASS) {
  			throw new IllegalStateException();
  		}
  		String str = element.asType().toString();
  		int i = str.lastIndexOf(".");
  		return str.substring(i + 1);
  	}
docs: Returns unqualified class name (e.g. String, if java.lang.String)
  NB: This method requires the given element has the kind of {@link ElementKind#CLASS}.
  @param element
  @return unqualified class name
  @author vvakame