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/**
 * Copyright (C) 2006-2015 phloc systems
 * http://www.phloc.com
 * office[at]phloc[dot]com
 *
 * 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.phloc.event.observerqueue;

import java.util.List;

import javax.annotation.Nonnull;

import com.phloc.commons.annotations.ReturnsMutableCopy;
import com.phloc.commons.state.EChange;
import com.phloc.event.IEventObserver;

/**
 * Interface for keeping a list of event observers.
 * 
 * @author philip
 */
public interface IEventObserverQueue
{
  /**
   * Add a new observer.
   * 
   * @param aObserver
   *        The observer to add. May not be null.
   * @return {@link EChange}
   */
  @Nonnull
  EChange addObserver (@Nonnull IEventObserver aObserver);

  /**
   * Remove a previously added observer.
   * 
   * @param aObserver
   *        The observer to remove. May not be null.
   * @return {@link EChange}
   */
  @Nonnull
  EChange removeObserver (@Nonnull IEventObserver aObserver);

  /**
   * @return A list of all observers. Never null
   */
  @Nonnull
  @ReturnsMutableCopy
  List  getAllObservers ();

  /**
   * @return true if not a single observer is contained,
   *         false if at least one observer is contained.
   */
  boolean isEmpty ();

  /**
   * This method is called before the main dispatching takes place. It is called
   * before each dispatch.
   */
  void beforeDispatch ();

  /**
   * This method is called after the main dispatching took place. It is called
   * after each dispatch.
   */
  void afterDispatch ();
}