An object is called a stateful object if it can be in more than one state and it exhibits different behaviors in different states. UML state machine diagrams can be used to model the various states that a single object (or system) may be in and the transitions between those states. An object may have a composite state, which has more than one independent area containing states and transitions. A subclass can inherit state behaviors from its superclasses. As an example, we show how to model the state behaviors of a radar system.