SourceMaking

class FSM {                                                 // 1. The "wrapper"

   private State[] states  = { new A(), new B(), new C() }; // 2. States array

   private int     current = 0;                             // 3. Current state

   public void on()  { states[current].on(  this ); }       // 4. Delegation

   public void off() { states[current].off( this ); }       //    and pass the

   public void ack() { states[current].ack( this ); }       //    this pointer

   public void changeState( int index ) { current = index; }

}

 

abstract class State {                               // 5. The State base class

   public void on(  FSM fsm ) { System.out.println( "error" ); } // 6. Default

   public void off( FSM fsm ) { System.out.println( "error" ); } //    behavior

   public void ack( FSM fsm ) { System.out.println( "error" ); }

}

 

class A extends State {

   public void on(  FSM fsm ) { System.out.println( "A + on  = C" );

      fsm.changeState( 2 ); }

   public void off( FSM fsm ) { System.out.println( "A + off = B" );

      fsm.changeState( 1 ); }

   public void ack( FSM fsm ) { System.out.println( "A + ack = A" );

      fsm.changeState( 0 ); }

}

 

class B extends State {

   public void on(  FSM fsm ) { System.out.println( "B + on  = A" );

      fsm.changeState( 0 ); }

   public void off( FSM fsm ) { System.out.println( "B + off = C" );

      fsm.changeState( 2 ); }

}

 

class C extends State {                  // 7. Only override some messages

   public void on( FSM fsm ) { System.out.println( "C + on  = B" );

      fsm.changeState( 1 ); }            // 8. "call back to" the wrapper class

}

 

public class StateDemo2 {

   public static void main( String[] args ) {

      FSM   fsm  = new FSM();

      int[] msgs = { 2, 1, 2, 1, 0, 2, 0, 0 };

      for (int i=0; i < msgs.length; i++)

         if      (msgs[i] == 0) fsm.on();

         else if (msgs[i] == 1) fsm.off();

         else if (msgs[i] == 2) fsm.ack();

}  }