Java設計模式-----State模式

　　源自

　　State模式

　　允許一個對象在其狀態改變時改變它的行為看起來對象似乎修改了它的類

　　例子

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    public interface State {
        public void handle(Context ctx);
    }

　　public class Context {

　　private State _state;

　　public Context(State state) {
            _state = state;
        }

　　public void request() {
            if (_state != null) {
                _statehandle(this);
            }
        }

　　public void ChangeState(State s) {
            if (_state != null) {
                _state = null;
            }
            _state = s;
        }
    }

　　public class ConcreteStateA implements State {

　　public void handle(Context ctx) {
            Systemoutprintln(handle by ConcreteStateA);
            if (ctx != null) {
                ctxChangeState(new ConcreteStateB());
            }
        }
    }

　　public class ConcreteStateB implements State {

　　public void handle(Context ctx) {
            Systemoutprintln(handle by ConcreteStateB);
            if (ctx != null) {
                ctxChangeState(new ConcreteStateA());
            }
        }
    }

　　public class StateClient {

　　public static void main(String[] args) {

　　State state = new ConcreteStateA();
            Context context = new Context(state);
            contextrequest();
            contextrequest();
            contextrequest();
            contextrequest();
        }
    }

From:http://tw.wingwit.com/Article/program/Java/hx/201311/25974.html