content: /*
   * Copyright (C) 2007 The Android Open Source Project
   *
   * 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 android.database;
  
  import java.util.ArrayList;
  
  /**
   * Provides methods for registering or unregistering arbitrary observers in an {@link ArrayList}.
   *
   * This abstract class is intended to be subclassed and specialized to maintain
   * a registry of observers of specific types and dispatch notifications to them.
   *
   * @param T The observer type.
   */
  public abstract class Observable<T> {
      /**
       * The list of observers.  An observer can be in the list at most
       * once and will never be null.
       */
      protected final ArrayList<T> mObservers = new ArrayList<T>();
  
      /**
       * Adds an observer to the list. The observer cannot be null and it must not already
       * be registered.
       * @param observer the observer to register
       * @throws IllegalArgumentException the observer is null
       * @throws IllegalStateException the observer is already registered
       */
      public void registerObserver(T observer) {
          if (observer == null) {
              throw new IllegalArgumentException("The observer is null.");
          }
          synchronized(mObservers) {
              if (mObservers.contains(observer)) {
                  throw new IllegalStateException("Observer " + observer + " is already registered.");
              }
              mObservers.add(observer);
          }
      }
  
      /**
       * Removes a previously registered observer. The observer must not be null and it
       * must already have been registered.
       * @param observer the observer to unregister
       * @throws IllegalArgumentException the observer is null
       * @throws IllegalStateException the observer is not yet registered
       */
      public void unregisterObserver(T observer) {
          if (observer == null) {
              throw new IllegalArgumentException("The observer is null.");
          }
          synchronized(mObservers) {
              int index = mObservers.indexOf(observer);
              if (index == -1) {
                  throw new IllegalStateException("Observer " + observer + " was not registered.");
              }
              mObservers.remove(index);
          }
      }
  
      /**
       * Remove all registered observers.
       */
      public void unregisterAll() {
          synchronized(mObservers) {
              mObservers.clear();
          }
      }
  }
  