content: /*
   * Copyright 1999-2018 Alibaba Group Holding Ltd.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package com.alibaba.nacos.common.notify.listener;
  
  import com.alibaba.nacos.common.notify.Event;
  
  import java.util.concurrent.Executor;
  
  /**
   * An abstract subscriber class for subscriber interface.
   *
   * @author <a href="mailto:liaochuntao@live.com">liaochuntao</a>
   * @author zongtanghu
   */
  @SuppressWarnings("PMD.AbstractClassShouldStartWithAbstractNamingRule")
  public abstract class Subscriber<T extends Event> {
      
      /**
       * Event callback.
       *
       * @param event {@link Event}
       */
      public abstract void onEvent(T event);
      
      /**
       * Type of this subscriber's subscription.
       *
       * @return Class which extends {@link Event}
       */
      public abstract Class<? extends Event> subscribeType();
      
      /**
       * It is up to the listener to determine whether the callback is asynchronous or synchronous.
       *
       * @return {@link Executor}
       */
      public Executor executor() {
          return null;
      }
      
      /**
       * Whether to ignore expired events.
       *
       * @return default value is {@link Boolean#FALSE}
       */
      public boolean ignoreExpireEvent() {
          return false;
      }
      
      /**
       * Whether the event's scope matches current subscriber. Default implementation is all scopes matched.
       * If you override this method, it better to override related {@link com.alibaba.nacos.common.notify.Event#scope()}.
       *
       * @param event {@link Event}
       * @return Whether the event's scope matches current subscriber
       */
      public boolean scopeMatches(T event) {
          return true;
      }
  }
  