开发模式：状态模式

状态模式中，行为是由状态来决定的，不同状态下有不同行为。
举个例子把，比如电视，电视有2个状态，一个是开机，一个是关机，开机时可以切换频道，关机时切换频道不做任何响应。

public interface TvState{
    public void nextChannerl();
    public void prevChannerl();
    public void turnUp();
    public void turnDown();
}

public class PowerOffState implements TvState{
    public void nextChannel(){}
    public void prevChannel(){}
    public void turnUp(){}
    public void turnDown(){}
    
}


public class PowerOnState implements TvState{
    public void nextChannel(){
        System.out.println("下一频道");
    }
    public void prevChannel(){
        System.out.println("上一频道");
    }
    public void turnUp(){
        System.out.println("调高音量");
    }
    public void turnDown(){
        System.out.println("调低音量"); 
    }
    
}

public interface PowerController{
    public void powerOn();
    public void powerOff();
}

public class TvController implements PowerController{
    TvState mTvState;
    public void setTvState(TvStete tvState){
        mTvState=tvState;
    }
    public void powerOn(){
        setTvState(new PowerOnState());
        System.out.println("开机啦");
    }
    public void powerOff(){
        setTvState(new PowerOffState());
        System.out.println("关机啦");
    }
    public void nextChannel(){
        mTvState.nextChannel();
    }
    public void prevChannel(){
        mTvState.prevChannel();
    }
    public void turnUp(){
        mTvState.turnUp();
    }
    public void turnDown(){
        mTvState.turnDown();
    }
    
}


public class Client{
    public static void main(String[] args){
        TvController tvController=new TvController();
        tvController.powerOn();
        tvController.nextChannel();
        tvController.turnUp();
        
        tvController.powerOff();
        //调高音量，此时不会生效
        tvController.turnUp();
    }


}