content: package act.util;
  
  /*-
   * #%L
   * ACT Framework
   * %%
   * Copyright (C) 2014 - 2017 ActFramework
   * %%
   * 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.
   * #L%
   */
  
  import org.osgl.util.E;
  
  /**
   * Application could extend this class to create singleton classes.
   * <p>
   *     Note, the sub type must NOT be abstract and has public constructor
   * </p>
   */
  public abstract class SingletonBase extends LogSupportedDestroyableBase {
  
      /**
       * Returns the singleton instance of the sub type
       * @param <T> the sub type of {@code SingletonBase}
       * @return the instance
       */
      public static <T> T instance() {
          throw E.tbd("This method will be enhanced on sub type of SingletonBase class");
      }
  
  }
  