oracle.ide.panels
Class FSM

java.lang.Object
  oracle.ide.panels.FSM

public final class FSM

extends java.lang.Object

FSM is a complete implementation of a finite state machine (a.k.a. deterministic finite automaton). The FSM is represented as a Map, so clients will need to provide a properly formatted Map object to initialize the FSM. The recommended way to build this Map is to use the FSMBuilder class, which provides an API abstraction for building the FSM data structure.

An FSM returns an FSMStateInfo every time a client class asks for the next or previous state. The interpretation of the FSMStateInfo object's contents is left to the client class's implementation.

The FSM encapsulates fairly complex behavior. An FSM:

• knows what the start state is.
• knows when it enters a final state.
• knows when it has halted (i.e. has completed the final state).
• maintains the internal state of the machine.
• keeps track of the current step number.
• can be reset to the start state.
• moves to the next FSM state given a transition.
• can step backwards through previous states.
• is able to handle sub-FSMs and can step backward through already halted sub-FSMs (restoring them to a non-halted state).

Note that reaching a final state does not necessarily mean that an FSM has halted. By definition, a halted FSM is one that has completed its final state (and a particular FSM specification may contain more than one final state). A final state is said to be "completed" when its activity (represented by the Step) has finished and Step's Traversable does not specify an exit transition that leaves the final state.

This means that it is possible to transition out of a final state into a non-final state or even another final state. The computational model for deterministic finite automata (DFA) allows for this, so this implementation simply follows suit. From a practical standpoint, most FSM's should need only one final state, and implementors should strive to have only one final state (with no transitions out of it) unless there is a specific feature that cannot be implemented otherwise.

The design of this class and its methods are based on the concepts behind the UML State Machine diagram, the UML Activity diagram, and the computational model of a deterministic finite automaton.

See Also:

FSMBuilder, Step, Traversable

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait