org.apache.commons.collections4.collection

## Class AbstractCollectionDecorator<E>

- java.lang.Object
- - org.apache.commons.collections4.collection.AbstractCollectionDecorator<E>

- Type Parameters:
    `E` - the type of the elements in the collection
  All Implemented Interfaces:
    Serializable, Iterable<E>, Collection<E>
  Direct Known Subclasses:
    AbstractBagDecorator, AbstractDualBidiMap.View, AbstractListDecorator, AbstractMultiSetDecorator, AbstractQueueDecorator, AbstractSetDecorator, IndexedCollection, PredicatedCollection, TransformedCollection, UnmodifiableBoundedCollection, UnmodifiableCollection

      public abstract class AbstractCollectionDecorator<E>
      extends Object
      implements Collection<E>, Serializable

  Decorates another `Collection` to provide additional behaviour.

  Each method call made on this `Collection` is forwarded to the decorated `Collection`. This class is used as a framework on which to build to extensions such as synchronized and unmodifiable behaviour. The main advantage of decoration is that one decorator can wrap any implementation of `Collection`, whereas sub-classing requires a new class to be written for each implementation.

  This implementation does not perform any special processing with `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.

  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 `Collections.unmodifiableCollection(Collection)`. Use an interface-specific subclass of AbstractCollectionDecorator, such as AbstractListDecorator, to preserve equality behavior, or override equals directly.

  Since:
    3.0
  See Also:
    Serialized Form

- - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `protected` | `AbstractCollectionDecorator()` Constructor only used in deserialization, do not use otherwise.
    `protected` | `AbstractCollectionDecorator(Collection<E> coll)` Constructor that wraps (not copies).

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `boolean` | `add(E object)`
    `boolean` | `addAll(Collection<? extends E> coll)`
    `void` | `clear()`
    `boolean` | `contains(Object object)`
    `boolean` | `containsAll(Collection<?> coll)`
    `protected Collection<E>` | `decorated()` Gets the collection being decorated.
    `boolean` | `isEmpty()`
    `Iterator<E>` | `iterator()`
    `boolean` | `remove(Object object)`
    `boolean` | `removeAll(Collection<?> coll)`
    `boolean` | `retainAll(Collection<?> coll)`
    `protected void` | `setCollection(Collection<E> coll)` Sets the collection being decorated.
    `int` | `size()`
    `Object[]` | `toArray()`
    `<T> T[]` | `toArray(T[] object)`
    `String` | `toString()`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

    - ### Methods inherited from interface java.util.Collection

      `equals, hashCode, parallelStream, removeIf, spliterator, stream`

    - ### Methods inherited from interface java.lang.Iterable

      `forEach`

- - ### Constructor Detail

    - #### AbstractCollectionDecorator

          protected AbstractCollectionDecorator()

      Constructor only used in deserialization, do not use otherwise.
      Since:
        3.1

    - #### AbstractCollectionDecorator

          protected AbstractCollectionDecorator(Collection<E> coll)

      Constructor that wraps (not copies).
      Parameters:
        `coll` - the collection to decorate, must not be null
      Throws:
        `NullPointerException` - if the collection is null

  - ### Method Detail

    - #### decorated

          protected Collection<E> decorated()

      Gets the collection being decorated. All access to the decorated collection goes via this method.
      Returns:
        the decorated collection

    - #### setCollection

          protected void setCollection(Collection<E> coll)

      Sets the collection being decorated.

      NOTE: this method should only be used during deserialization

      Parameters:
        `coll` - the decorated collection

    - #### add

          public boolean add(E object)

      Specified by:
        `add` in interface `Collection<E>`

    - #### addAll

          public boolean addAll(Collection<? extends E> coll)

      Specified by:
        `addAll` in interface `Collection<E>`

    - #### clear

          public void clear()

      Specified by:
        `clear` in interface `Collection<E>`

    - #### contains

          public boolean contains(Object object)

      Specified by:
        `contains` in interface `Collection<E>`

    - #### isEmpty

          public boolean isEmpty()

      Specified by:
        `isEmpty` in interface `Collection<E>`

    - #### iterator

          public Iterator<E> iterator()

      Specified by:
        `iterator` in interface `Iterable<E>`
      Specified by:
        `iterator` in interface `Collection<E>`

    - #### remove

          public boolean remove(Object object)

      Specified by:
        `remove` in interface `Collection<E>`

    - #### size

          public int size()

      Specified by:
        `size` in interface `Collection<E>`

    - #### toArray

          public Object[] toArray()

      Specified by:
        `toArray` in interface `Collection<E>`

    - #### toArray

          public <T> T[] toArray(T[] object)

      Specified by:
        `toArray` in interface `Collection<E>`

    - #### containsAll

          public boolean containsAll(Collection<?> coll)

      Specified by:
        `containsAll` in interface `Collection<E>`

    - #### removeAll

          public boolean removeAll(Collection<?> coll)

      Specified by:
        `removeAll` in interface `Collection<E>`

    - #### retainAll

          public boolean retainAll(Collection<?> coll)

      Specified by:
        `retainAll` in interface `Collection<E>`

    - #### toString

          public String toString()

      Overrides:
        `toString` in class `Object`

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