在狀態(tài)模式（State Pattern）中，類的行為是基于它的狀態(tài)改變的。
允許對(duì)象在內(nèi)部狀態(tài)發(fā)生改變時(shí)改變它的行為，對(duì)象看起來好像修改了它的類。

狀態(tài)模式.png

public class Context {

    private State state;

    public Context(){
        state = null;
    }

    public void setState(State state){

        this.state = state;
    }

    public State getState(){

        return this.state;
    }
}

public interface State {

    public void doAction(Context context);
}

public class StartState implements State {

    @Override
    public void doAction(Context context) {

        System.out.println("start state");
        context.setState(this);
    }
}

public class StopState implements State {

    @Override
    public void doAction(Context context) {

        System.out.println("stop state");
        context.setState(this);
    }
}

public class StateDemo {

    public static void main(String[] args){

        Context context = new Context();

        StartState startState = new StartState();
        startState.doAction(context);

        StopState stopState = new StopState();
        stopState.doAction(context);
    }
}