状态模式(State Pattern)

    在状态模式中，一个类的行为基于它的状态的改变而改变。状态模式归属于行为型模式。     在下面的实例中，我们创建了一个接口State，定义了一个操作方法，两个实现类StartState和StopState。另外，创建了一个上下文类Context，这个类关联到State类。UML类图如下所示：     状态类State 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"; } } 实现类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"; } } 上下文类Context.java 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StatePatternDemo.java 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()); } } 输出结果： Player is in start state Start State Player is in stop state Stop State