public abstract class

AbstractCollection

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

Class Overview

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.
[Expand]
Inherited Methods
From class java.lang.Object
From interface java.lang.Iterable
From interface java.util.Collection

Protected Constructors

protected AbstractCollection ()

Since: API Level 1

Constructs a new instance of this AbstractCollection.

Public Methods

public 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.

public 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). 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 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 void clear ()

Since: API Level 1

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

public boolean contains (Object object)

Since: API Level 1

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 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 boolean containsAll (Collection<?> collection)

Since: API Level 1

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 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 boolean isEmpty ()

Since: API Level 1

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

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 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.

public boolean remove (Object object)

Since: API Level 1

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 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 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.

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 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 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.

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 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.

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.

public T[] toArray (T[] contents)

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
contents the array.
Returns
  • an array of the elements from this Collection.

public 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.

public String toString ()

Since: API Level 1

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.