E
- the type of the elements in the collectionpublic abstract class AbstractCollectionDecorator<E> extends Object implements Collection<E>, Serializable
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.
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) |
boolean |
isEmpty() |
Iterator<E> |
iterator() |
boolean |
remove(Object object) |
boolean |
removeAll(Collection<?> coll) |
boolean |
removeIf(Predicate<? super E> filter) |
boolean |
retainAll(Collection<?> coll) |
int |
size() |
Object[] |
toArray() |
<T> T[] |
toArray(T[] object) |
String |
toString() |
equals, getClass, hashCode, notify, notifyAll, wait, wait, wait
equals, hashCode, parallelStream, spliterator, stream
public boolean add(E object)
add
in interface Collection<E>
public boolean addAll(Collection<? extends E> coll)
addAll
in interface Collection<E>
public void clear()
clear
in interface Collection<E>
public boolean contains(Object object)
contains
in interface Collection<E>
public boolean isEmpty()
isEmpty
in interface Collection<E>
public boolean remove(Object object)
remove
in interface Collection<E>
public int size()
size
in interface Collection<E>
public Object[] toArray()
toArray
in interface Collection<E>
public <T> T[] toArray(T[] object)
toArray
in interface Collection<E>
public boolean containsAll(Collection<?> coll)
containsAll
in interface Collection<E>
public boolean removeIf(Predicate<? super E> filter)
removeIf
in interface Collection<E>
public boolean removeAll(Collection<?> coll)
removeAll
in interface Collection<E>
public boolean retainAll(Collection<?> coll)
retainAll
in interface Collection<E>
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