public abstract class AbstractCollection<E>

  1. Object
  2. AbstractCollection

ImplementsCollection<E>, Iterable<E>

Known subtypesAbstractList, AbstractQueue, AbstractSet, ArrayDeque

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.

Constructors

protected AbstractCollection()Constructs a new instance of this AbstractCollection.

Methods

public boolean add(E object)Attempts to add object to the contents of this Collection (optional).
public boolean addAll(Collection<? extends E> collection)Attempts to add all of the objects contained in collection to the contents of this Collection (optional).
public void clear()Removes all elements from this Collection, leaving it empty (optional).
public boolean contains(Object object)Tests whether this Collection contains the specified object.
public boolean containsAll(Collection<?> collection)Tests whether this Collection contains all objects contained in the specified Collection.
public boolean isEmpty()Returns if this Collection contains no elements.
public abstract Iterator<E> iterator()Returns an instance of Iterator that may be used to access the objects contained by this Collection.
public boolean remove(Object object)Removes one instance of the specified object from this Collection if one is contained (optional).
public boolean removeAll(Collection<?> collection)Removes all occurrences in this Collection of each object in the specified Collection (optional).
public boolean retainAll(Collection<?> collection)Removes all objects from this Collection that are not also found in the Collection passed (optional).
public abstract int size()Returns a count of how many objects this Collection contains.
public String toString()Returns the string representation of this Collection.
public Object[] toArray()Returns a new array containing all elements contained in this ArrayList.
public <T> T[] toArray(T[] contents)Returns an array containing all elements contained in this ArrayList.

Inherited methods

From Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait, clone

From Collection

removeIf

From Iterable

forEach

Constructor details

AbstractCollection

protected AbstractCollection()
Constructs a new instance of this AbstractCollection.

Method details

add

public 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

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.

addAll

public 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<? extends E>
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.

clear

public 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

public 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

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

public 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

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.

isEmpty

public boolean isEmpty()
Returns if this Collection contains no elements. This implementation tests, whether size returns 0.

Returns

true if this Collection has no elements, false otherwise.

See also

iterator

public abstract 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

an iterator for accessing the Collection contents.

remove

public 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

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

public 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

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.

retainAll

public 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

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.

size

public abstract 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

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

toString

public 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

the string representation of this Collection.

toArray

public Object[] toArray()
Returns a new array containing all elements contained in this ArrayList.

Returns

an array of the elements from this ArrayList

toArray

public <T> T[] toArray(T[] contents)
Returns an array containing all elements contained in this ArrayList. 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 ArrayList, the array element following the collection elements is set to null.

Parameters

contents T[]
the array.

Returns

an array of the elements from this ArrayList.

Throws

ArrayStoreException
when the type of an element in this ArrayList cannot be stored in the type of the specified array.