Summary: Methods | Inherited Methods | [Expand All]

public interface

Collection

implements Iterable<T>

java.util.Collection<E>

Known Indirect Subclasses

AbstractCollection<E>, AbstractList<E>, AbstractQueue<E>, AbstractSequentialList<E>, AbstractSet<E>, ArrayBlockingQueue<E>, ArrayDeque<E>, ArrayList<E>, BlockingDeque<E>, BlockingQueue<E>, ConcurrentLinkedQueue<E>, ConcurrentSkipListSet<E>, CopyOnWriteArrayList<E>, CopyOnWriteArraySet<E>, DelayQueue<E extends Delayed>, Deque<E>, EnumSet<E extends Enum<E>>, HashSet<E>, LinkedBlockingDeque<E>, LinkedBlockingQueue<E>, LinkedHashSet<E>, LinkedList<E>, List<E>, NavigableSet<E>, PriorityBlockingQueue<E>, PriorityQueue<E>, Queue<E>, Set<E>, SortedSet<E>, Stack<E>, SynchronousQueue<E>, TreeSet<E>, Vector<E>

AbstractCollection<E>	Class `AbstractCollection` is an abstract implementation of the `Collection` interface.
AbstractList<E>	`AbstractList` is an abstract implementation of the `List` interface, optimized for a backing store which supports random access.
AbstractQueue<E>	AbstractQueue is an abstract class which implements some of the methods in `Queue`.
AbstractSequentialList<E>	AbstractSequentialList is an abstract implementation of the List interface.
AbstractSet<E>	An AbstractSet is an abstract implementation of the Set interface.
ArrayBlockingQueue<E>	A bounded `blocking queue` backed by an array.
ArrayDeque<E>	An implementation of Deque, backed by an array.
ArrayList<E>	ArrayList is an implementation of `List`, backed by an array.
BlockingDeque<E>	A `Deque` that additionally supports blocking operations that wait for the deque to become non-empty when retrieving an element, and wait for space to become available in the deque when storing an element.
BlockingQueue<E>	A `Queue` that additionally supports operations that wait for the queue to become non-empty when retrieving an element, and wait for space to become available in the queue when storing an element.
ConcurrentLinkedQueue<E>	An unbounded thread-safe `queue` based on linked nodes.
ConcurrentSkipListSet<E>	A scalable concurrent `NavigableSet` implementation based on a `ConcurrentSkipListMap`.
CopyOnWriteArrayList<E>	Implements a `ArrayList` variant that is thread-safe.
CopyOnWriteArraySet<E>	A `Set` that uses an internal `CopyOnWriteArrayList` for all of its operations.
DelayQueue<E extends Delayed>	An unbounded `blocking queue` of `Delayed` elements, in which an element can only be taken when its delay has expired.
Deque<E>	A kind of collection that can insert or remove element at both ends("double ended queue").
EnumSet<E extends Enum<E>>	An EnumSet is a specialized Set to be used with enums as keys.
HashSet<E>	HashSet is an implementation of a Set.
LinkedBlockingDeque<E>	An optionally-bounded `blocking deque` based on linked nodes.
LinkedBlockingQueue<E>	An optionally-bounded `blocking queue` based on linked nodes.
LinkedHashSet<E>	LinkedHashSet is a variant of HashSet.
LinkedList<E>	LinkedList is an implementation of `List`, backed by a doubly-linked list.
List<E>	A `List` is a collection which maintains an ordering for its elements.
NavigableSet<E>	NavigableSet is a SortedSet with navigation methods answering the closest matches for specified item.
PriorityBlockingQueue<E>	An unbounded `blocking queue` that uses the same ordering rules as class `PriorityQueue` and supplies blocking retrieval operations.
PriorityQueue<E>	A PriorityQueue holds elements on a priority heap, which orders the elements according to their natural order or according to the comparator specified at construction time.
Queue<E>	This kind of collection provides advanced operations compared to basic collections, such as insertion, extraction, and inspection.
Set<E>	A `Set` is a data structure which does not allow duplicate elements.
SortedSet<E>	SortedSet is a Set which iterates over its elements in a sorted order.
Stack<E>	`Stack` is a Last-In/First-Out(LIFO) data structure which represents a stack of objects.
SynchronousQueue<E>	A `blocking queue` in which each insert operation must wait for a corresponding remove operation by another thread, and vice versa.
TreeSet<E>	TreeSet is an implementation of SortedSet.
Vector<E>	Vector is an implementation of `List`, backed by an array and synchronized.

Class Overview

Collection is the root of the collection hierarchy. It defines operations on data collections and the behavior that they will have in all implementations of Collections. All direct or indirect implementations of Collection should implement at least two constructors. One with no parameters which creates an empty collection and one with a parameter of type Collection. This second constructor can be used to create a collection of different type as the initial collection but with the same elements. Implementations of Collection cannot be forced to implement these two constructors but at least all implementations under java.util do. Methods that change the content of a collection throw an UnsupportedOperationException if the underlying collection does not support that operation, though it's not mandatory to throw such an Exception in cases where the requested operation would not change the collection. In these cases it's up to the implementation whether it throws an UnsupportedOperationException or not. Methods marked with (optional) can throw an UnsupportedOperationException if the underlying collection doesn't support that method.

Summary

Public Methods
abstract boolean	add(E object) Attempts to add `object` to the contents of this `Collection` (optional).
abstract boolean	addAll(Collection<? extends E> collection) Attempts to add all of the objects contained in `Collection` to the contents of this `Collection` (optional).
abstract void	clear() Removes all elements from this `Collection`, leaving it empty (optional).
abstract boolean	contains(Object object) Tests whether this `Collection` contains the specified object.
abstract boolean	containsAll(Collection<?> collection) Tests whether this `Collection` contains all objects contained in the specified `Collection`.
abstract boolean	equals(Object object) Compares the argument to the receiver, and returns true if they represent the same object using a class specific comparison.
abstract int	hashCode() Returns an integer hash code for the receiver.
abstract boolean	isEmpty() Returns if this `Collection` contains no elements.
abstract Iterator<E>	iterator() Returns an instance of `Iterator` that may be used to access the objects contained by this `Collection`.
abstract boolean	remove(Object object) Removes one instance of the specified object from this `Collection` if one is contained (optional).
abstract boolean	removeAll(Collection<?> collection) Removes all occurrences in this `Collection` of each object in the specified `Collection` (optional).
abstract boolean	retainAll(Collection<?> collection) Removes all objects from this `Collection` that are not also found in the `Collection` passed (optional).
abstract int	size() Returns a count of how many objects this `Collection` contains.
abstract <T> T[]	toArray(T[] array) Returns an array containing all elements contained in this `Collection`.
abstract Object[]	toArray() Returns a new array containing all elements contained in this `Collection`.

[Expand]

Inherited Methods

From interface java.lang.Iterable

Public Methods

public abstract boolean add (E object)

Since: API Level 1

Attempts to add object to the contents of this Collection (optional). After this method finishes successfully it is guaranteed that the object is contained in the collection. If the collection was modified it returns true, false if no changes were made. An implementation of Collection may narrow the set of accepted objects, but it has to specify this in the documentation. If the object to be added does not meet this restriction, then an IllegalArgumentException is thrown. If a collection does not yet contain an object that is to be added and adding the object fails, this method must throw an appropriate unchecked Exception. Returning false is not permitted in this case because it would violate the postcondition that the element will be part of the collection after this method finishes.

Parameters

object	the object to add.

Returns

true if this Collection is modified, false otherwise.

Throws

UnsupportedOperationException	if adding to this `Collection` is not supported.
ClassCastException	if the class of the object is inappropriate for this collection.
IllegalArgumentException	if the object cannot be added to this `Collection`.
NullPointerException	if null elements cannot be added to the `Collection`.

public abstract boolean addAll (Collection<? extends E> collection)

Since: API Level 1

Attempts to add all of the objects contained in Collection to the contents of this Collection (optional). If the passed Collection is changed during the process of adding elements to this Collection, the behavior is not defined.

Parameters

collection	the `Collection` of objects.

Returns

true if this Collection is modified, false otherwise.

Throws

UnsupportedOperationException	if adding to this `Collection` is not supported.
ClassCastException	if the class of an object is inappropriate for this `Collection`.
IllegalArgumentException	if an object cannot be added to this `Collection`.
NullPointerException	if `collection` is `null`, or if it contains `null` elements and this `Collection` does not support such elements.

public abstract void clear ()

Since: API Level 1

Removes all elements from this Collection, leaving it empty (optional).

Throws

UnsupportedOperationException	if removing from this `Collection` is not supported.

public abstract boolean contains (Object object)

Since: API Level 1

Tests whether this Collection contains the specified object. Returns true if and only if at least one element elem in this Collection meets following requirement: (object==null ? elem==null : object.equals(elem)).

Parameters

object	the object to search for.

Returns

true if object is an element of this Collection, false otherwise.

Throws

ClassCastException	if the object to look for isn't of the correct type.
NullPointerException	if the object to look for is `null` and this `Collection` doesn't support `null` elements.

public abstract boolean containsAll (Collection<?> collection)

Since: API Level 1

Tests whether this Collection contains all objects contained in the specified Collection. If an element elem is contained several times in the specified Collection, the method returns true even if elem is contained only once in this Collection.

Parameters

collection	the collection of objects.

Returns

true if all objects in the specified Collection are elements of this Collection, false otherwise.

Throws

ClassCastException	if one or more elements of `collection` isn't of the correct type.
NullPointerException	if `collection` contains at least one `null` element and this `Collection` doesn't support `null` elements.
NullPointerException	if `collection` is `null`.

public abstract boolean equals (Object object)

Since: API Level 1

Compares the argument to the receiver, and returns true if they represent the same object using a class specific comparison.

Parameters

object	the object to compare with this object.

Returns

true if the object is the same as this object and false if it is different from this object.

public abstract int hashCode ()

Since: API Level 1

Returns an integer hash code for the receiver. Objects which are equal return the same value for this method.

Returns

the receiver's hash.

public abstract boolean isEmpty ()

Since: API Level 1

Returns if this Collection contains no elements.

Returns

true if this Collection has no elements, false otherwise.

public abstract Iterator<E> iterator ()

Since: API Level 1

Returns an instance of Iterator that may be used to access the objects contained by this Collection. The order in which the elements are returned by the iterator is not defined. Only if the instance of the Collection has a defined order the elements are returned in that order.

Returns

an iterator for accessing the Collection contents.

public abstract boolean remove (Object object)

Since: API Level 1

Removes one instance of the specified object from this Collection if one is contained (optional). The element elem that is removed complies with (object==null ? elem==null : object.equals(elem).

Parameters

object	the object to remove.

Returns

true if this Collection is modified, false otherwise.

Throws

UnsupportedOperationException	if removing from this `Collection` is not supported.
ClassCastException	if the object passed is not of the correct type.
NullPointerException	if `object` is `null` and this `Collection` doesn't support `null` elements.

public abstract boolean removeAll (Collection<?> collection)

Since: API Level 1

Removes all occurrences in this Collection of each object in the specified Collection (optional). After this method returns none of the elements in the passed Collection can be found in this Collection anymore.

Parameters

collection	the collection of objects to remove.

Returns

true if this Collection is modified, false otherwise.

Throws

UnsupportedOperationException	if removing from this `Collection` is not supported.
ClassCastException	if one or more elements of `collection` isn't of the correct type.
NullPointerException	if `collection` contains at least one `null` element and this `Collection` doesn't support `null` elements.
NullPointerException	if `collection` is `null`.

public abstract boolean retainAll (Collection<?> collection)

Since: API Level 1

Removes all objects from this Collection that are not also found in the Collection passed (optional). After this method returns this Collection will only contain elements that also can be found in the Collection passed to this method.

Parameters

collection	the collection of objects to retain.

Returns

true if this Collection is modified, false otherwise.

Throws

UnsupportedOperationException	if removing from this `Collection` is not supported.
ClassCastException	if one or more elements of `collection` isn't of the correct type.
NullPointerException	if `collection` contains at least one `null` element and this `Collection` doesn't support `null` elements.
NullPointerException	if `collection` is `null`.

public abstract int size ()

Since: API Level 1

Returns a count of how many objects this Collection contains.

Returns

how many objects this Collection contains, or Integer.MAX_VALUE if there are more than Integer.MAX_VALUE elements in this Collection.

public abstract T[] toArray (T[] array)

Since: API Level 1

Returns an array containing all elements contained in this Collection. If the specified array is large enough to hold the elements, the specified array is used, otherwise an array of the same type is created. If the specified array is used and is larger than this Collection, the array element following the Collection elements is set to null. If the implementation has ordered elements it will return the element array in the same order as an iterator would return them. toArray(new Object[0]) behaves exactly the same way as toArray() does.

Parameters

array	the array.

Returns

an array of the elements from this Collection.

Throws

ArrayStoreException	if the type of an element in this `Collection` cannot be stored in the type of the specified array.

public abstract Object[] toArray ()

Since: API Level 1

Returns a new array containing all elements contained in this Collection. If the implementation has ordered elements it will return the element array in the same order as an iterator would return them. The array returned does not reflect any changes of the Collection. A new array is created even if the underlying data structure is already an array.

Returns

an array of the elements from this Collection.

Interfaces

Classes

Enums

Exceptions

Errors

Collection

Class Overview

Summary

Public Methods

public abstract boolean add (E object)

Parameters

Returns

Throws

public abstract boolean addAll (Collection<? extends E> collection)

Parameters

Returns

Throws

public abstract void clear ()

Throws

See Also

public abstract boolean contains (Object object)

Parameters

Returns

Throws

public abstract boolean containsAll (Collection<?> collection)

Parameters

Returns

Throws

public abstract boolean equals (Object object)

Parameters

Returns

See Also

public abstract int hashCode ()

Returns

See Also

public abstract boolean isEmpty ()

Returns

See Also

public abstract Iterator<E> iterator ()

Returns

public abstract boolean remove (Object object)

Parameters

Returns

Throws

public abstract boolean removeAll (Collection<?> collection)

Parameters

Returns

Throws

public abstract boolean retainAll (Collection<?> collection)

Parameters

Returns

Throws

public abstract int size ()

Returns

public abstract T[] toArray (T[] array)

Parameters

Returns

Throws

public abstract Object[] toArray ()

Returns