整理Java有限状态机

2017-10-12

246字, 约2分钟读完

有限状态机FSM及它的构成要素

The FSM can change from one state to another in response to some external inputs; the change from one state to another is called a transition. An FSM is defined by a list of its states, its initial state, and the conditions for each transition.

有限状态机由状态集合, 初始状态, 状态转移条件定义。

Java实现

根据FSM定义，可以抽象出Java的3种数据类型：

状态(State)
事件(Event)
事件触发状态转移，是状态机的输入。
上下文(Context)
上下文，可以包含各种Condition。

例子：当前状态A，此时输入事件E，如果满足条件C，会导致状态A转换到状态B。这种情况下，A,B是State，E是Event，C是Context下的Condition。

具体代码

状态机运行

public State run() {
    for (State s = initState; s != null; s = s.next(context)) {
    // do something here
    }
    return state;
}

State, Event用Enum, 且State一定包含next() method

public enum State {

    INIT(0, "未初始化") {
        @Override
        public State next(Context context) {
            switch (context.getEvent()) {
                case Event1:
                    return context.condition1() ? STATE_1 : STATE_2;
                default:
                    return null;
            }
        }
    },
    STATE_1(1, "状态1") {
        @Override
        public State next(Context context) {
            context.setState(STATE_1);
            switch (context.getEvent()) {
                case Event1:
                    return context.condition2() ? STATE_3 : null;
                default:
                    return null;
            }
        }
    };

    private Byte code;
    private String desc;

    State(int code, String desc) {
        this.code = (byte) code;
        this.desc = desc;
    }

    public abstract State next(Context context);
}

Context是一系列Condition组合得到的interface

public interface Context {
    void setState(State state);

    /**
     * 得到Event input
     * @return
     */
    EventEnum getEvent();

    /**
     * 是否满足条件1
     * @return
     */
    Boolean condition1();
}

组合得到FSM的定义

class FSM implements Context {

     private EventEnum event;

     private State    state;

     public FSM(State initState) {
         this.state = initState;
     }

     public State run() {
         for (State s = initState; s != null; s = s.next(this)) {
         }
         return state;
     }

     @Override
     public EventEnum getEvent() {
         return event;
     }

     //implements conditions 
}

有限状态机FSM及它的构成要素

Java实现

具体代码

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