title: Set a value at most once with the builder pattern
body: <p>Is there a standard practice in Java, while using the builder pattern, to ensure that a member variable is set at most once. I need to make sure that the setter is called 0 or 1 times but never more. I would like to throw a <code>RuntimeException</code> of some type but am worried about synchronization issues as well as best-practices in this area. </p>