/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You 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 org.apache.commons.collections4.collection;
  
  import java.io.Serializable;
  import java.util.Collection;
  import java.util.Iterator;
  import java.util.Objects;
  import java.util.function.Predicate;
  
  /**
   * Decorates another {@code Collection} to provide additional behavior.
   * <p>
   * Each method call made on this {@code Collection} is forwarded to the
   * decorated {@code Collection}. This class is used as a framework on which
   * to build to extensions such as synchronized and unmodifiable behavior. The
   * main advantage of decoration is that one decorator can wrap any implementation
   * of {@code Collection}, whereas sub-classing requires a new class to be
   * written for each implementation.
   * </p>
   * <p>
   * This implementation does not perform any special processing with
   * {@link #iterator()}. Instead it simply returns the value from the
   * wrapped collection. This may be undesirable, for example if you are trying
   * to write an unmodifiable implementation it might provide a loophole.
   * </p>
   * <p>
   * This implementation does not forward the hashCode and equals methods through
   * to the backing object, but relies on Object's implementation. This is necessary
   * to preserve the symmetry of equals. Custom definitions of equality are usually
   * based on an interface, such as Set or List, so that the implementation of equals
   * can cast the object being tested for equality to the custom interface.
   * AbstractCollectionDecorator does not implement such custom interfaces directly;
   * they are implemented only in subclasses. Therefore, forwarding equals would break
   * symmetry, as the forwarding object might consider itself equal to the object being
   * tested, but the reverse could not be true. This behavior is consistent with the
   * JDK's collection wrappers, such as {@link java.util.Collections#unmodifiableCollection(Collection)}.
   * Use an interface-specific subclass of AbstractCollectionDecorator, such as
   * AbstractListDecorator, to preserve equality behavior, or override equals directly.
   * </p>
   *
   * @param <E> the type of the elements in the collection
   * @since 3.0
   */
  public abstract class AbstractCollectionDecorator<E>
          implements Collection<E>, Serializable {
  
      /** Serialization version */
      private static final long serialVersionUID = 6249888059822088500L;
  
      /** The collection being decorated */
      private Collection<E> collection;
  
      /**
       * Constructor only used in deserialization, do not use otherwise.
       * @since 3.1
       */
      protected AbstractCollectionDecorator() {
      }
  
      /**
       * Constructor that wraps (not copies).
       *
       * @param collection  the collection to decorate, must not be null
       * @throws NullPointerException if the collection is null
       */
      protected AbstractCollectionDecorator(final Collection<E> collection) {
          this.collection = Objects.requireNonNull(collection, "collection");
      }
  
      @Override
      public boolean add(final E object) {
          return decorated().add(object);
      }
  
      @Override
      public boolean addAll(final Collection<? extends E> coll) {
          return decorated().addAll(coll);
      }
  
      @Override
      public void clear() {
          decorated().clear();
      }
  
     @Override
     public boolean contains(final Object object) {
         return decorated().contains(object);
     }
 
     @Override
     public boolean containsAll(final Collection<?> coll) {
         return decorated().containsAll(coll);
     }
 
     /**
      * Gets the collection being decorated.
      * All access to the decorated collection goes via this method.
      *
      * @return the decorated collection
      */
     protected Collection<E> decorated() {
         return collection;
     }
 
     @Override
     public boolean isEmpty() {
         return decorated().isEmpty();
     }
 
     @Override
     public Iterator<E> iterator() {
         return decorated().iterator();
     }
 
     @Override
     public boolean remove(final Object object) {
         return decorated().remove(object);
     }
 
     @Override
     public boolean removeAll(final Collection<?> coll) {
         return decorated().removeAll(coll);
     }
 
     /**
      * @since 4.4
      */
     @Override
     public boolean removeIf(final Predicate<? super E> filter) {
         return decorated().removeIf(filter);
     }
 
     @Override
     public boolean retainAll(final Collection<?> coll) {
         return decorated().retainAll(coll);
     }
 
     /**
      * Sets the collection being decorated.
      * <p>
      * <b>NOTE:</b> this method should only be used during deserialization
      *
      * @param coll  the decorated collection
      */
     protected void setCollection(final Collection<E> coll) {
         this.collection = coll;
     }
 
     @Override
     public int size() {
         return decorated().size();
     }
 
     @Override
     public Object[] toArray() {
         return decorated().toArray();
     }
 
     @Override
     public <T> T[] toArray(final T[] object) {
         return decorated().toArray(object);
     }
 
     @Override
     public String toString() {
         return decorated().toString();
     }
 
 }