Java 状态模式实现

文章目录

状态模式
- State
- Event
- Action
- ActionContext
测试
- 相关实现
- Test

状态模式

相关组件有状态(State)，事件(Event)，动作(Action)，状态机(ActionContext)。

通过红绿灯可以获得一个demo：
有三种状态：红色，绿色，黄色；
有一种事件：灯改变事件；
有三种动作：红变绿，绿变黄，黄变红；

State

标识状态。

package fsm;


public abstract class State {

    public String getName() {
        return this.getClass().getSimpleName();
    }

    @Override
    public String toString() {
        return getName() + "{}";
    }
}

Event

表示事件。

package fsm;


public abstract class Event {

    public String getName() {
        return this.getClass().getSimpleName();
    }

    @Override
    public String toString() {
        return getName() + "{}";
    }
}

Action

表示动作，在指定的State下，发生指定Event便会调用Action进行操作，并返回下一状态。

package fsm;

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;


public abstract class Action {

    public Class getStateType() {
        return (Class) getGenericType(0);
    }

    public Class getEventType() {
        return (Class) getGenericType(1);
    }

    private Type getGenericType(int i) {
        return ((ParameterizedType) this.getClass().getGenericSuperclass()).getActualTypeArguments()[i];
    }

    
    public abstract State handle(S state, E event);

    @Override
    public String toString() {
        return this.getClass().getSimpleName() + "{" + getStateType().getSimpleName()
                + "," + getEventType().getSimpleName() +
                "}";
    }
}

ActionContext
整个Action的上下文，也就是状态机。

package fsm; import java.util.ArrayList; import java.util.List; public class ActionContext { private State currentState; private List actions = new ArrayList<>(); public ActionContext(State currentState) { this.currentState = currentState; } public void addAction(Action action) { actions.add(action); } public ActionContext handle(Event event) { for (Action action : actions) { if (action.getEventType().isInstance(event) && action.getStateType().isInstance(currentState)) { currentState = action.handle(currentState, event); break; } } return this; } @Override public String toString() { return "ActionContext{" + "currentState=" + currentState + ", actions=" + actions + '}'; } }
测试相关实现
红绿灯状态的转变。
GreenAction，RedAction，YellowAction类似。

package fsm.action; import fsm.Action; import fsm.State; import fsm.event.ChangeEvent; import fsm.state.GreenState; import fsm.state.YellowState; public class GreenAction extends Action { @Override public State handle(GreenState state, ChangeEvent event) { System.out.println("GreenAction:" + state + "," + event); return new YellowState(); } }

RedState，YellowState，GreenState类似

package fsm.state; import fsm.State; public class GreenState extends State { }

ChangeEvent：改变事件

package fsm.event; import fsm.Event; public class ChangeEvent extends Event { }
Test
package fsm; import fsm.action.GreenAction; import fsm.action.RedAction; import fsm.action.YellowAction; import fsm.event.ChangeEvent; import fsm.state.RedState; public class Test { public static void main(String[] args) { ActionContext context = new ActionContext(new RedState()); context.addAction(new RedAction()); context.addAction(new GreenAction()); context.addAction(new YellowAction()); System.out.println(context); context.handle(new ChangeEvent()); System.out.println(context); context.handle(new ChangeEvent()); System.out.println(context); context.handle(new ChangeEvent()); System.out.println(context); } }

Java 状态模式实现

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