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Added in API level 1

AbstractCollection

public abstract class AbstractCollection
extends Object implements Collection<E>

java.lang.Object
   ↳ java.util.AbstractCollection<E>
Known Direct Subclasses
Known Indirect Subclasses


Class AbstractCollection is an abstract implementation of the Collection interface. A subclass must implement the abstract methods iterator() and size() to create an immutable collection. To create a modifiable collection it's necessary to override the add() method that currently throws an UnsupportedOperationException.

Summary

Protected constructors

AbstractCollection()

Constructs a new instance of this AbstractCollection.

Public methods

boolean add(E object)

Attempts to add object to the contents of this Collection (optional).

boolean addAll(Collection<? extends E> collection)

Attempts to add all of the objects contained in collection to the contents of this Collection (optional).

void clear()

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

boolean contains(Object object)

Tests whether this Collection contains the specified object.

boolean containsAll(Collection<?> collection)

Tests whether this Collection contains all objects contained in the specified Collection.

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.

boolean remove(Object object)

Removes one instance of the specified object from this Collection if one is contained (optional).

boolean removeAll(Collection<?> collection)

Removes all occurrences in this Collection of each object in the specified Collection (optional).

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.

<T> T[] toArray(T[] contents)

Returns an array containing all elements contained in this Collection.

Object[] toArray()

Returns a new array containing all elements contained in this Collection.

String toString()

Returns the string representation of this Collection.

Inherited methods

From class java.lang.Object
From interface java.util.Collection
From interface java.lang.Iterable

Protected constructors

AbstractCollection

Added in API level 1
AbstractCollection ()

Constructs a new instance of this AbstractCollection.

Public methods

add

Added in API level 1
boolean add (E object)

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 E: the object to add.
Returns
boolean true if this Collection is modified, false otherwise.

addAll

Added in API level 1
boolean addAll (Collection<? extends E> collection)

Attempts to add all of the objects contained in collection to the contents of this Collection (optional). This implementation iterates over the given Collection and calls add for each element. If any of these calls return true, then true is returned as result of this method call, false otherwise. If this Collection does not support adding elements, an UnsupportedOperationException is thrown.

If the passed Collection is changed during the process of adding elements to this Collection, the behavior depends on the behavior of the passed Collection.

Parameters
collection Collection: the collection of objects.
Returns
boolean 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.

clear

Added in API level 1
void clear ()

Removes all elements from this Collection, leaving it empty (optional). This implementation iterates over this Collection and calls the remove method on each element. If the iterator does not support removal of elements, an UnsupportedOperationException is thrown.

Concrete implementations usually can clear a Collection more efficiently and should therefore overwrite this method.

Throws
UnsupportedOperationException it the iterator does not support removing elements from this Collection

See also:

contains

Added in API level 1
boolean contains (Object object)

Tests whether this Collection contains the specified object. This implementation iterates over this Collection and tests, whether any element is equal to the given object. If object != null then object.equals(e) is called for each element e returned by the iterator until the element is found. If object == null then each element e returned by the iterator is compared with the test e == null.

Parameters
object Object: the object to search for.
Returns
boolean 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.

containsAll

Added in API level 1
boolean containsAll (Collection<?> collection)

Tests whether this Collection contains all objects contained in the specified Collection. This implementation iterates over the specified Collection. If one element returned by the iterator is not contained in this Collection, then false is returned; true otherwise.

Parameters
collection Collection: the collection of objects.
Returns
boolean 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.

isEmpty

Added in API level 1
boolean isEmpty ()

Returns if this Collection contains no elements. This implementation tests, whether size returns 0.

Returns
boolean true if this Collection has no elements, false otherwise.

See also:

iterator

Added in API level 1
Iterator<E> iterator ()

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 unless the instance of the Collection has a defined order. In that case, the elements are returned in that order.

In this class this method is declared abstract and has to be implemented by concrete Collection implementations.

Returns
Iterator<E> an iterator for accessing the Collection contents.

remove

Added in API level 1
boolean remove (Object object)

Removes one instance of the specified object from this Collection if one is contained (optional). This implementation iterates over this Collection and tests for each element e returned by the iterator, whether e is equal to the given object. If object != null then this test is performed using object.equals(e), otherwise using object == null. If an element equal to the given object is found, then the remove method is called on the iterator and true is returned, false otherwise. If the iterator does not support removing elements, an UnsupportedOperationException is thrown.

Parameters
object Object: the object to remove.
Returns
boolean 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.

removeAll

Added in API level 1
boolean removeAll (Collection<?> collection)

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.

This implementation iterates over this Collection and tests for each element e returned by the iterator, whether it is contained in the specified Collection. If this test is positive, then the remove method is called on the iterator. If the iterator does not support removing elements, an UnsupportedOperationException is thrown.

Parameters
collection Collection: the collection of objects to remove.
Returns
boolean 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.

retainAll

Added in API level 1
boolean retainAll (Collection<?> collection)

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.

This implementation iterates over this Collection and tests for each element e returned by the iterator, whether it is contained in the specified Collection. If this test is negative, then the remove method is called on the iterator. If the iterator does not support removing elements, an UnsupportedOperationException is thrown.

Parameters
collection Collection: the collection of objects to retain.
Returns
boolean 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.

size

Added in API level 1
int size ()

Returns a count of how many objects this Collection contains.

In this class this method is declared abstract and has to be implemented by concrete Collection implementations.

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

toArray

Added in API level 1
T[] toArray (T[] contents)

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
contents T: the array.
Returns
T[] an array of the elements from this Collection.

toArray

Added in API level 1
Object[] toArray ()

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
Object[] an array of the elements from this Collection.

toString

Added in API level 1
String toString ()

Returns the string representation of this Collection. The presentation has a specific format. It is enclosed by square brackets ("[]"). Elements are separated by ', ' (comma and space).

Returns
String the string representation of this Collection.
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