State Transition Diagram Introduction

The simplest use of this library is to create state transition diagrams. Consider for example, the following workflow of an Agile Product Owner who reviews a story that has just been developed:

Although you can chose any object to represent the states and actions, enum is a natural choice, so they may look something like this:

enum ReviewState {
    Developed, RequiresChanges, Modified, Approved, Rejected
}

enum Action {
    Review, Approve, Modify, Reject
}

To create the state transition diagram, you simply instantiate it and add the states:

StateTransitionTable<ReviewState, Action> table = 
        new StateTransitionTable<ReviewState, Action>();
    table.addTransition(ReviewState.Developed, Action.Approve, ReviewState.Approved);
    table.addTransition(ReviewState.Developed, Action.Review, ReviewState.RequiresChanges);
    table.addTransition(ReviewState.Developed, Action.Reject, ReviewState.Rejected);
    table.addTransition(ReviewState.RequiresChanges, Action.Modify, ReviewState.Modified);
    table.addTransition(ReviewState.Modified, Action.Review, ReviewState.RequiresChanges);
    table.addTransition(ReviewState.Modified, Action.Reject, ReviewState.Rejected);
    table.addTransition(ReviewState.Modified, Action.Approve, ReviewState.Approved);

The state transition diagram created above can be used to obtain the next valid state given the current state and an action, or validate weather an action is valid for a particular state. Here is a (unit test) example:

assertEquals(ReviewState.Rejected, table.getNextState(ReviewState.Modified, Action.Reject));
    try {
        table.getNextState(ReviewState.Rejected, Action.Approve);
    } catch (InvalidTransitionException ite) {
        assertEquals("There is no transition from state Rejected on symbol Approve.", ite.getMessage());
    }