IT工程師數位筆記本

public interface Customer{}
public class VIP : Customer{
  public void Serve(){}
}

public static void main(String[] args){
  Customer customer = new VIP();
  Serve(customer);
}
public static void Serve(Customer customer){
  VIP vip = (VIP)customer;
  vip.Serve();
}

/**
 * @class
 * @private
 * @description 幫助類
 */
class Utils{
        /* @method 對用戶輸入的filter進行加工 
         * @static
         * @package
         * @param {DOMString|Function} origFilter - 用戶輸出的filter
         * @returns {Function}
         * @exception
         */
        static wrapFilter(origFilter){
            var type = typeof origFilter
            if ('string' === type) return message => RegExp(origFilter, 'i').test(message.topic)
            else if ('function' === type) return origFilter
            throw Error('the type of argument(0) is wrong, which accepts string or function instance only!')
        }
        /* @method 添加消息到消息隊列
         * @static
         * @package
         * @param {Array.<Message>} mq - 消息隊列
         * @param {Message} message - 被添加的消息實例
         * @param {Object.<{Number} GUIDofTimer, {Number} pause>} timer - 定時執行器
         */
        static addMessage(mq, message, timer){
                timer.pause = 1
                if (!(timer.pause = mq.length)) return mq.push(message)
                for(var i = 0, inserted = 0, m; !inserted && (m = mq[i]); ++i) 
                    if(inserted = m.priority < message.priority)
                        mq.splice(i, 0, message)
                if(!inserted) mq.push(message)
                timer.pause = 0
        }
        /* @method 分發消息給訂閱者
         * @static
         * @package
         * @param {Array.<Message>} mq - 消息隊列
         * @param {Array} subs - 訂閱者池 
         * @returns {Array.<Message>} - 未被響應的消息回收隊列
         */
        static dispatch(mq, subs){
            var message, unresponsedMq = []
            while(message = mq.shift()){
                    let found = 0
                    for(let sub of subs) if(sub.filter(message) && ++found)
                        sub.handler(message)
                    if (!found) unresponsedMq.push(message)
            }
            return unresponsedMq
        }
        static doUnsub(subs, pred){
            var sub, remainSubs = []
            while(sub = subs.shift()) if(pred());else
                remainSubs.push(sub)
            return remainSubs
        }
}

/**
 * @class
 * @private
 * @description 消息類
 */
class Message{
        constructor(topic, content, priority = 0){
                this.topic = topic
                this.content = content
                this.priority = priority
        }
}

/**
 * @class
 * @public
 * @description 消息中轉站
 */
export default class MrB{
        constructor(during = 10){
            this.mq = []
            this.subs = []
            // dispatch message to subscribers, then recycle unhandled messages
            this.timer = {timer: setInterval(()=>{
                        if (this.timer.pause) return
                        this.mq = Utils.dispatch(this.mq, this.subs)
                    }, during)}
        }
        /* @method 訂閱消息
         * @public
         * @param {DOMString|Function} filter - 消息過濾器
         * @param {Function} handler - 消息響應函數
         * @returns {DOMString} - 訂閱編號，用于退訂
         */
        sub(filter, handler){
                var guid = (+new Date()) + '' + 100000*Math.random()
                this.subs.push({guid: guid, filter: Utils.wrapFilter(filter), handler: handler})
                return guid
        }

        /* @method 退訂 
         * @public 
         * @param {DOMString|Function} filter/guid - 消息過濾器 或 訂閱編號
         * @param {Function} [handler] - 消息響應函數
         */
        unsub(filter/*or guid*/, handler){
                this.subs = Utils.doUnsub(this.subs, handler 
                                ? (sub)=>sub.filter.toString() === filter.toString() && sub.handler.toString() === handler.toString()
                                : (sub)=>sub.guid === filter.toString() || sub.filter.toString() === filter.toString())
        }

        /* @method 發布消息
         * @public
         * @param {DOMString|Object|Message} topic - 消息主題 或 消息實體
         * @param {DOMString} [content=''] - 消息內容
         * @param {Number} [priority=0] - 消息優先級
         */
        pub(topic, content = '', priority = 0){
                var message
                if(1 === arguments.length) message = (topic.priority = topic.priority || 0, topic)
                else message = new Message(topic, content, priority)
                
                // push message to mq
                Utils.addMessage(this.mq, message, this.timer)
        }
}