怎么在java项目中使用State状态模式

//状态类 public interface State {   public void doAction(Context context); } //实现类StartState.java public class StartState implements State {   public void doAction(Context context) {    System.out.println("Player is in start state");    context.setState(this);    }   public String toString(){    return "Start State";   } } //实现StopState.java public class StopState implements State {   public void doAction(Context context) {    System.out.println("Player is in stop state");    context.setState(this);    }   public String toString(){    return "Stop State";   } }  //上下文Context.java 实际运用时可自行更改 public class Context {   private State state;   public Context(){    state = null;   }   public void setState(State state){    this.state = state;           }   public State getState(){    return state;   } }  //测试类 public class StatePatternDemo {   public static void main(String[] args) {    Context context = new Context();    StartState startState = new StartState();    startState.doAction(context);    System.out.println(context.getState().toString());      StopState stopState = new StopState();    stopState.doAction(context);      System.out.println(context.getState().toString());   } }