Merging state and command pattern with enum and interface

A post just for the fun :-) I would like to describe how to simply merge the state and command design patterns while using enum and interface in java.

We have for instance a class having a changing state :

public MyClass {
protected IState currentState = new MyState.INIT;
...... // other instance variables
...... // some methods

public void myMethod() {
if(aCondition)
currentState = currentState.nextState();
else
currentState = currentState.previousState();
currentState.execAction();
}
}

We can define the interface IState as follow :

public Interface IState {
public void execAction();
public void undoAction();
public IState nextState();
public IState previousState();
}

A dummy state for the fun :

public enum DummyState implements IState {
NIL ; // only one state

public void execAction(){}; // nothing by default
public void undoAction(){}; // nothing by default
public IEtat nextState(){
return this;
};
public IState previousState(){
return this;
};
}

And then a state MyState :

public enum MyState implements IState {

INIT {

public IState nextState(){ return IN_PROGRESS;}

public IState previousState() { return INIT;}

},

IN_PROGRESS {

public IState nextState(){ return TERMINATED;}

public IState previousState() { return INIT;}

},

SUSPENDED {

public IState nextState(){ return IN_PROGRESS;}

public IState previousState() { return IN_PROGRESS;}

},

TERMINATED {

public void execAction(){

Action anAction = new Action();

anAction.exec();

actionsDone.add(anAction);

};

public IState nextState(){ return ARCHIVED;}

public IState previousState() { return IN_PROGRESS;}

},

ARCHIVED {

public IState nextState(){ return DummyState.NIL;}

public IState previousState() { return TERMINATED;}

}

Vector actionsDone = new Vector();

public void execAction(){}; // nothing by default
public void undoAction(){}; // nothing by default

public IState nextState(){
return this;
};

public IEtat previousState(){
return this;
};

}

And finally the Action :

public Class Action extends Command {
public exec() {
//something to do
}
}