状态模式主要解决,当控制一个对象状态的条件表达式过于复杂时的情况;把状态的判断逻辑转移到表示不同状态的一系列类中,可以把复杂的判断逻辑简化;状态模式的角色:上下文环境(Context)角色、抽象状态(State)角色、具体状态(Concrete State)和客户端(Client)角色;状态模式的案例:实现类图:实现代码:/** * 上下文环境(Context)角色 */public class Context {private State state;public Context() {state = null;}public void setState(State state) {this.state = state;}public State getState() {return state;}}/** * 抽象状态(State)角色 */public interface State { public void doAction(Context context); }/** * 具体状态(Concrete State) */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";}}/** * 具体状态(Concrete State) */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";}}/** * 客户端 */public class Client {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());}}
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