状态模式

• State
• 状态便于扩展, 方法不便扩展。如果相反用switch

  • public class MM {
        MMState state;
        public void smile(){
            state.smile();
        }
    }
    public abstract class MMState {
        abstract void smile();
    }
    public class MMHappyState extends MMState {
        @Override
        void smile(){}
    }

• FSM例子，线程状态

  • public class Thread_ {
        ThreadState_ state;
        void move(Action a) { state.move(a);}
    }
    abstract class ThreadState_ {
        abstract void move(Action a);
    }
    public class NewState extends ThreadState_ {
        private Thread_ t;
        @Override
        void move(Action a) {
            if ("start".equals(a.msg)) {
                t.state = new RunningState(t);
            }
        }
    }
    public class Action {
        String msg;
    }