ForwardingCollection (Guava: Google Core Libraries for Java 27.0-jre API)

java.lang.Object
- com.google.common.collect.ForwardingObject
- - com.google.common.collect.ForwardingCollection<E>

All Implemented Interfaces:

Iterable<E>, Collection<E>

Direct Known Subclasses:

ForwardingList, ForwardingMultiset, ForwardingQueue, ForwardingSet
```
@GwtCompatible
public abstract class ForwardingCollection<E>
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 Summary

Constructors
Modifier Constructor and Description

protected ForwardingCollection()
Constructor for use by subclasses.

Constructors
Modifier	Constructor and Description
`protected`	`ForwardingCollection()` Constructor for use by subclasses.

Method Summary

All Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method and Description
`boolean`	`add(E element)` Ensures that this collection contains the specified element (optional operation).
`boolean`	`addAll(Collection<? extends E> collection)` Adds all of the elements in the specified collection to this collection (optional operation).
`void`	`clear()` Removes all of the elements from this collection (optional operation).
`boolean`	`contains(Object object)` Returns `true` if this collection contains the specified element.
`boolean`	`containsAll(Collection<?> collection)` Returns `true` if this collection contains all of the elements in the specified collection.
`protected abstract Collection<E>`	`delegate()` Returns the backing delegate instance that methods are forwarded to.
`boolean`	`isEmpty()` Returns `true` if this collection contains no elements.
`Iterator<E>`	`iterator()` Returns an iterator over the elements in this collection.
`boolean`	`remove(Object object)` Removes a single instance of the specified element from this collection, if it is present (optional operation).
`boolean`	`removeAll(Collection<?> collection)` Removes all of this collection's elements that are also contained in the specified collection (optional operation).
`boolean`	`retainAll(Collection<?> collection)` Retains only the elements in this collection that are contained in the specified collection (optional operation).
`int`	`size()` Returns the number of elements in this collection.
`protected boolean`	`standardAddAll(Collection<? extends E> collection)` A sensible definition of `addAll(java.util.Collection<? extends E>)` in terms of `add(E)`.
`protected void`	`standardClear()` A sensible definition of `clear()` in terms of `iterator()`, using the iterator's `remove` method.
`protected boolean`	`standardContains(@Nullable Object object)` A sensible definition of `contains(java.lang.Object)` in terms of `iterator()`.
`protected boolean`	`standardContainsAll(Collection<?> collection)` A sensible definition of `containsAll(java.util.Collection<?>)` in terms of `contains(java.lang.Object)` .
`protected boolean`	`standardIsEmpty()` A sensible definition of `isEmpty()` as `!iterator().hasNext`.
`protected boolean`	`standardRemove(@Nullable Object object)` A sensible definition of `remove(java.lang.Object)` in terms of `iterator()`, using the iterator's `remove` method.
`protected boolean`	`standardRemoveAll(Collection<?> collection)` A sensible definition of `removeAll(java.util.Collection<?>)` in terms of `iterator()`, using the iterator's `remove` method.
`protected boolean`	`standardRetainAll(Collection<?> collection)` A sensible definition of `retainAll(java.util.Collection<?>)` in terms of `iterator()`, using the iterator's `remove` method.
`protected Object[]`	`standardToArray()` A sensible definition of `toArray()` in terms of `toArray(Object[])`.
`protected <T> T[]`	`standardToArray(T[] array)` A sensible definition of `toArray(Object[])` in terms of `size()` and `iterator()`.
`protected String`	`standardToString()` A sensible definition of `ForwardingObject.toString()` in terms of `iterator()`.
`Object[]`	`toArray()` Returns an array containing all of the elements in this collection.
`<T> T[]`	`toArray(T[] array)` Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.

Methods inherited from class com.google.common.collect.ForwardingObject
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
  - ForwardingCollection
```
protected ForwardingCollection()
```
    Constructor for use by subclasses.
- 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 Iterable<E>
    
    Specified by:
    
    iterator in interface Collection<E>
    
    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>
    
    Returns:
    
    the number of elements in this collection
  - removeAll
```
@CanIgnoreReturnValue
public boolean removeAll(Collection<?> collection)
```
    Description copied from interface: java.util.Collection
    
    Removes all of this collection's elements that are also contained in the specified collection (optional operation). After this call returns, this collection will contain no elements in common with the specified collection.
    
    Specified by:
    
    removeAll in interface Collection<E>
    
    Parameters:
    
    collection - collection containing elements to be removed from this collection
    
    Returns:
    
    true if this collection changed as a result of the call
    
    See Also:
    
    Collection.remove(Object), Collection.contains(Object)
  - isEmpty
```
public boolean isEmpty()
```
    Description copied from interface: java.util.Collection
    
    Returns true if this collection contains no elements.
    
    Specified by:
    
    isEmpty in interface Collection<E>
    
    Returns:
    
    true if this collection contains no elements
  - contains
```
public boolean contains(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 (o==null ? e==null : o.equals(e)).
    
    Specified by:
    
    contains in interface Collection<E>
    
    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>
    
    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(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 (o==null ? e==null : o.equals(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>
    
    Parameters:
    
    object - element to be removed from this collection, if present
    
    Returns:
    
    true if an element was removed as a result of this call
  - containsAll
```
public boolean containsAll(Collection<?> collection)
```
    Description copied from interface: java.util.Collection
    
    Returns true if this collection contains all of the elements in the specified collection.
    
    Specified by:
    
    containsAll in interface Collection<E>
    
    Parameters:
    
    collection - collection to be checked for containment in this collection
    
    Returns:
    
    true if this collection contains all of the elements in the specified collection
    
    See Also:
    
    Collection.contains(Object)
  - 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>
    
    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)
  - retainAll
```
@CanIgnoreReturnValue
public boolean retainAll(Collection<?> collection)
```
    Description copied from interface: java.util.Collection
    
    Retains only the elements in this collection that are contained in the specified collection (optional operation). In other words, removes from this collection all of its elements that are not contained in the specified collection.
    
    Specified by:
    
    retainAll in interface Collection<E>
    
    Parameters:
    
    collection - collection containing elements to be retained in this collection
    
    Returns:
    
    true if this collection changed as a result of the call
    
    See Also:
    
    Collection.remove(Object), Collection.contains(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>
  - toArray
```
public 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 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.
    This method acts as bridge between array-based and collection-based APIs.
    
    Specified by:
    
    toArray in interface Collection<E>
    
    Returns:
    
    an array containing all of the elements in this collection
  - toArray
```
@CanIgnoreReturnValue
public <T> 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.
    Like the Collection.toArray() method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs.
    Suppose x is a collection known to contain only strings. The following code can be used to dump the collection into a newly allocated array of String:
```
     String[] y = x.toArray(new String[0]);
```
    Note that toArray(new Object[0]) is identical in function to toArray().
    Specified by:
    
    toArray in interface Collection<E>
    
    Type Parameters:
    
    T - the runtime 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
  - standardContains
```
protected boolean standardContains(@Nullable Object object)
```
    A sensible definition of contains(java.lang.Object) in terms of iterator(). If you override iterator(), you may wish to override contains(java.lang.Object) to forward to this implementation.
    
    Since:
    
    7.0
  - standardContainsAll
```
protected boolean standardContainsAll(Collection<?> collection)
```
    A sensible definition of containsAll(java.util.Collection<?>) in terms of contains(java.lang.Object) . If you override contains(java.lang.Object), you may wish to override containsAll(java.util.Collection<?>) to forward to this implementation.
    
    Since:
    
    7.0
  - standardAddAll
```
protected boolean standardAddAll(Collection<? extends E> collection)
```
    A sensible definition of addAll(java.util.Collection<? extends E>) in terms of add(E). If you override add(E), you may wish to override addAll(java.util.Collection<? extends E>) to forward to this implementation.
    
    Since:
    
    7.0
  - standardRemove
```
protected boolean standardRemove(@Nullable Object object)
```
    A sensible definition of remove(java.lang.Object) in terms of iterator(), using the iterator's remove method. If you override iterator(), you may wish to override remove(java.lang.Object) to forward to this implementation.
    
    Since:
    
    7.0
  - standardRemoveAll
```
protected boolean standardRemoveAll(Collection<?> collection)
```
    A sensible definition of removeAll(java.util.Collection<?>) in terms of iterator(), using the iterator's remove method. If you override iterator(), you may wish to override removeAll(java.util.Collection<?>) to forward to this implementation.
    
    Since:
    
    7.0
  - standardRetainAll
```
protected boolean standardRetainAll(Collection<?> collection)
```
    A sensible definition of retainAll(java.util.Collection<?>) in terms of iterator(), using the iterator's remove method. If you override iterator(), you may wish to override retainAll(java.util.Collection<?>) to forward to this implementation.
    
    Since:
    
    7.0
  - 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
  - standardToString
```
protected String standardToString()
```
    A sensible definition of ForwardingObject.toString() in terms of iterator(). If you override iterator(), you may wish to override ForwardingObject.toString() to forward to this implementation.
    
    Since:
    
    7.0
  - standardToArray
```
protected Object[] standardToArray()
```
    A sensible definition of toArray() in terms of toArray(Object[]). If you override toArray(Object[]), you may wish to override toArray() to forward to this implementation.
    
    Since:
    
    7.0
  - standardToArray
```
protected <T> T[] standardToArray(T[] array)
```
    A sensible definition of toArray(Object[]) in terms of size() and iterator(). If you override either of these methods, you may wish to override toArray() to forward to this implementation.
    
    Since:
    
    7.0

Class ForwardingCollection<E>

Constructor Summary

Method Summary

Methods inherited from class com.google.common.collect.ForwardingObject

Methods inherited from class java.lang.Object

Methods inherited from interface java.util.Collection

Methods inherited from interface java.lang.Iterable

Constructor Detail

ForwardingCollection

Method Detail

delegate

iterator

size

removeAll

isEmpty

contains

add

remove

containsAll

addAll

retainAll

clear

toArray

toArray

standardContains

standardContainsAll

standardAddAll

standardRemove

standardRemoveAll

standardRetainAll

standardClear

standardIsEmpty

standardToString

standardToArray

standardToArray