Package com.google.common.collect

Class ForwardingCollection<E extends @Nullable Object>

  • All Implemented Interfaces:
    Iterable<E>, Collection<E>
    Direct Known Subclasses:
    ForwardingList, ForwardingMultiset, ForwardingQueue, ForwardingSet
    @GwtCompatible
public abstract class ForwardingCollection<E extends @Nullable Object>
extends ForwardingObject
implements Collection<E>
    A collection which forwards all its method calls to another collection. Subclasses should override one or more methods to modify the behavior of the backing collection as desired per the decorator pattern.

    Warning: The methods of ForwardingCollection forward indiscriminately to the methods of the delegate. For example, overriding add(E) alone will not change the behavior of addAll(java.util.Collection<? extends E>), which can lead to unexpected behavior. In this case, you should override addAll as well, either providing your own implementation, or delegating to the provided standardAddAll method.

    default method warning: This class does not forward calls to default methods. Instead, it inherits their default implementations. When those implementations invoke methods, they invoke methods on the ForwardingCollection.

    The standard methods are not guaranteed to be thread-safe, even when all of the methods that they depend on are thread-safe.

    Since:
    2.0
    Author:
    Kevin Bourrillion, Louis Wasserman

    • Constructor Detail

    • Method Detail

      • delegate

        protected abstract Collection<E> delegate()
        Description copied from class: ForwardingObject
        Returns the backing delegate instance that methods are forwarded to. Abstract subclasses generally override this method with an abstract method that has a more specific return type, such as ForwardingSet.delegate(). Concrete subclasses override this method to supply the instance being decorated.
        Specified by:
        delegate in class ForwardingObject

      • iterator

        public Iterator<E> iterator()
        Description copied from interface: java.util.Collection
        Returns an iterator over the elements in this collection. There are no guarantees concerning the order in which the elements are returned (unless this collection is an instance of some class that provides a guarantee).
        Specified by:
        iterator in interface Collection<E extends @Nullable Object>
        Specified by:
        iterator in interface Iterable<E extends @Nullable Object>
        Returns:
        an Iterator over the elements in this collection

      • size

        public int size()
        Description copied from interface: java.util.Collection
        Returns the number of elements in this collection. If this collection contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.
        Specified by:
        size in interface Collection<E extends @Nullable Object>
        Returns:
        the number of elements in this collection

      • contains

        public boolean contains​(@CheckForNull
                        Object object)
        Description copied from interface: java.util.Collection
        Returns true if this collection contains the specified element. More formally, returns true if and only if this collection contains at least one element e such that Objects.equals(o, e).
        Specified by:
        contains in interface Collection<E extends @Nullable Object>
        Parameters:
        object - element whose presence in this collection is to be tested
        Returns:
        true if this collection contains the specified element

      • add

        @CanIgnoreReturnValue
public boolean add​(E element)
        Description copied from interface: java.util.Collection
        Ensures that this collection contains the specified element (optional operation). Returns true if this collection changed as a result of the call. (Returns false if this collection does not permit duplicates and already contains the specified element.)

        Collections that support this operation may place limitations on what elements may be added to this collection. In particular, some collections will refuse to add null elements, and others will impose restrictions on the type of elements that may be added. Collection classes should clearly specify in their documentation any restrictions on what elements may be added.

        If a collection refuses to add a particular element for any reason other than that it already contains the element, it must throw an exception (rather than returning false). This preserves the invariant that a collection always contains the specified element after this call returns.

        Specified by:
        add in interface Collection<E extends @Nullable Object>
        Parameters:
        element - element whose presence in this collection is to be ensured
        Returns:
        true if this collection changed as a result of the call

      • remove

        @CanIgnoreReturnValue
public boolean remove​(@CheckForNull
                      Object object)
        Description copied from interface: java.util.Collection
        Removes a single instance of the specified element from this collection, if it is present (optional operation). More formally, removes an element e such that Objects.equals(o, e), if this collection contains one or more such elements. Returns true if this collection contained the specified element (or equivalently, if this collection changed as a result of the call).
        Specified by:
        remove in interface Collection<E extends @Nullable Object>
        Parameters:
        object - element to be removed from this collection, if present
        Returns:
        true if an element was removed as a result of this call

      • addAll

        @CanIgnoreReturnValue
public boolean addAll​(Collection<? extends E> collection)
        Description copied from interface: java.util.Collection
        Adds all of the elements in the specified collection to this collection (optional operation). The behavior of this operation is undefined if the specified collection is modified while the operation is in progress. (This implies that the behavior of this call is undefined if the specified collection is this collection, and this collection is nonempty.)
        Specified by:
        addAll in interface Collection<E extends @Nullable Object>
        Parameters:
        collection - collection containing elements to be added to this collection
        Returns:
        true if this collection changed as a result of the call
        See Also:
        Collection.add(Object)

      • clear

        public void clear()
        Description copied from interface: java.util.Collection
        Removes all of the elements from this collection (optional operation). The collection will be empty after this method returns.
        Specified by:
        clear in interface Collection<E extends @Nullable Object>

      • toArray

        public @Nullable Object[] toArray()
        Description copied from interface: java.util.Collection
        Returns an array containing all of the elements in this collection. If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order. The returned array's runtime component type is Object.

        The returned array will be "safe" in that no references to it are maintained by this collection. (In other words, this method must allocate a new array even if this collection is backed by an array). The caller is thus free to modify the returned array.

        Specified by:
        toArray in interface Collection<E extends @Nullable Object>
        Returns:
        an array, whose runtime component type is Object, containing all of the elements in this collection

      • toArray

        @CanIgnoreReturnValue
public <T extends @Nullable Object> T[] toArray​(T[] array)
        Description copied from interface: java.util.Collection
        Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. If the collection fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this collection.

        If this collection fits in the specified array with room to spare (i.e., the array has more elements than this collection), the element in the array immediately following the end of the collection is set to null. (This is useful in determining the length of this collection only if the caller knows that this collection does not contain any null elements.)

        If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.

        Specified by:
        toArray in interface Collection<E extends @Nullable Object>
        Type Parameters:
        T - the component type of the array to contain the collection
        Parameters:
        array - the array into which the elements of this collection are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.
        Returns:
        an array containing all of the elements in this collection

      • standardClear

        protected void standardClear()
        A sensible definition of clear() in terms of iterator(), using the iterator's remove method. If you override iterator(), you may wish to override clear() to forward to this implementation.
        Since:
        7.0

      • standardIsEmpty

        protected boolean standardIsEmpty()
        A sensible definition of isEmpty() as !iterator().hasNext. If you override isEmpty(), you may wish to override isEmpty() to forward to this implementation. Alternately, it may be more efficient to implement isEmpty as size() == 0.
        Since:
        7.0