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JAVA.UTIL
CLASS ABSTRACTCOLLECTION<E>

java.lang.Object
  java.util.AbstractCollection<E>


All Implemented Interfaces: Iterable<E>, Collection<E> Direct Known Subclasses:
AbstractList, AbstractQueue, AbstractSet

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public abstract class AbstractCollection<E>extends Objectimplements Collection<E>

This class provides a skeletal implementation of the Collection interface, to
minimize the effort required to implement this interface.

To implement an unmodifiable collection, the programmer needs only to extend
this class and provide implementations for the iterator and size methods. (The
iterator returned by the iterator method must implement hasNext and next.)

To implement a modifiable collection, the programmer must additionally override
this class's add method (which otherwise throws an
UnsupportedOperationException), and the iterator returned by the iterator method
must additionally implement its remove method.

The programmer should generally provide a void (no argument) and Collection
constructor, as per the recommendation in the Collection interface
specification.

The documentation for each non-abstract methods in this class describes its
implementation in detail. Each of these methods may be overridden if the
collection being implemented admits a more efficient implementation.

This class is a member of the Java Collections Framework.





Since: 1.2 See Also:Collection

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Constructor Summary protected AbstractCollection()
          Sole constructor.

 

Method Summary  boolean add(E o)
          Ensures that this collection contains the specified element (optional
operation).  boolean addAll(Collection<? extends E> c)
          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 o)
          Returns true if this collection contains the specified element.
 boolean containsAll(Collection<?> c)
          Returns true if this collection contains all of the elements in the
specified collection.  boolean isEmpty()
          Returns true if this collection contains no elements. abstract
 Iterator<E> iterator()
          Returns an iterator over the elements contained in this collection.
 boolean remove(Object o)
          Removes a single instance of the specified element from this
collection, if it is present (optional operation).  boolean
removeAll(Collection<?> c)
          Removes from this collection all of its elements that are contained in
the specified collection (optional operation).  boolean
retainAll(Collection<?> c)
          Retains only the elements in this collection that are contained in the
specified collection (optional operation). abstract  int size()
          Returns the number of elements in this collection.  Object[] toArray()
          Returns an array containing all of the elements in this collection.

<T> T[]

toArray(T[] a)
          Returns an array containing all of the elements in this collection;
the runtime type of the returned array is that of the specified array.  String
toString()
          Returns a string representation of this collection.

 

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

 



Constructor Detail


ABSTRACTCOLLECTION

protected AbstractCollection()

Sole constructor. (For invocation by subclass constructors, typically implicit.)



Method Detail


ITERATOR

public abstract Iterator<E> iterator()

Returns an iterator over the elements contained in this collection.



Specified by:iterator in interface Iterable<E>Specified by:iterator in interface
Collection<E> Returns:an iterator over the elements contained in this
collection.

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SIZE

public abstract int size()

Returns the number of elements in this collection. If the 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.

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ISEMPTY

public boolean isEmpty()

Returns true if this collection contains no elements.

This implementation returns size() == 0.



Specified by:isEmpty in interface Collection<E> Returns:true if this collection
contains no elements.

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CONTAINS

public boolean contains(Object o)

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)).

This implementation iterates over the elements in the collection, checking each
element in turn for equality with the specified element.



Specified by:contains in interface Collection<E> Parameters:o - object to be
checked for containment in this collection. Returns:true if this collection
contains the specified element.

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TOARRAY

public Object[] toArray()

Returns an array containing all of the elements in this collection. If the
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 the
collection. (In other words, this method must allocate a new array even if the
collection is backed by an Array). The caller is thus free to modify the
returned array.

This implementation allocates the array to be returned, and iterates over the
elements in the collection, storing each object reference in the next
consecutive element of the array, starting with element 0.



Specified by:toArray in interface Collection<E> Returns:an array containing all
of the elements in this collection.

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TOARRAY

public <T> T[] toArray(T[] a)

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 the collection fits in the specified array with room to spare (i.e., the
array has more elements than the 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 the collection only if the caller knows that the
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.

This implementation checks if the array is large enough to contain the
collection; if not, it allocates a new array of the correct size and type (using
reflection). Then, it iterates over the collection, storing each object
reference in the next consecutive element of the array, starting with element 0.
If the array is larger than the collection, a null is stored in the first
location after the end of the collection.



Specified by:toArray in interface Collection<E> Parameters:a - the array into
which the elements of the 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 the elements of the collection. Throws:
NullPointerException - if the specified array is null. ArrayStoreException - if
the runtime type of the specified array is not a supertype of the runtime type
of every element in this collection.

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ADD

public boolean add(E o)

Ensures that this collection contains the specified element (optional
operation). Returns true if the 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 the 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.

This implementation always throws an UnsupportedOperationException.



Specified by:add in interface Collection<E> Parameters:o - element whose
presence in this collection is to be ensured. Returns:true if the collection
changed as a result of the call. Throws: UnsupportedOperationException - if the
add method is not supported by this collection. NullPointerException - if this
collection does not permit null elements, and the specified element is null.
ClassCastException - if the class of the specified element prevents it from
being added to this collection. IllegalArgumentException - if some aspect of
this element prevents it from being added to this collection.

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REMOVE

public boolean remove(Object o)

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 the collection contains one or more such
elements. Returns true if the collection contained the specified element (or
equivalently, if the collection changed as a result of the call).

This implementation iterates over the collection looking for the specified
element. If it finds the element, it removes the element from the collection
using the iterator's remove method.

Note that this implementation throws an UnsupportedOperationException if the
iterator returned by this collection's iterator method does not implement the
remove method and this collection contains the specified object.



Specified by:remove in interface Collection<E> Parameters:o - element to be
removed from this collection, if present. Returns:true if the collection
contained the specified element. Throws: UnsupportedOperationException - if the
remove method is not supported by this collection.

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CONTAINSALL

public boolean containsAll(Collection<?> c)

Returns true if this collection contains all of the elements in the specified
collection.

This implementation iterates over the specified collection, checking each
element returned by the iterator in turn to see if it's contained in this
collection. If all elements are so contained true is returned, otherwise false.



Specified by:containsAll in interface Collection<E> Parameters:c - collection to
be checked for containment in this collection. Returns:true if this collection
contains all of the elements in the specified collection. Throws:
NullPointerException - if the specified collection is null.See
Also:contains(Object)

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ADDALL

public boolean addAll(Collection<? extends E> c)

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.)

This implementation iterates over the specified collection, and adds each object
returned by the iterator to this collection, in turn.

Note that this implementation will throw an UnsupportedOperationException unless
add is overridden (assuming the specified collection is non-empty).



Specified by:addAll in interface Collection<E> Parameters:c - collection whose
elements are to be added to this collection. Returns:true if this collection
changed as a result of the call. Throws: UnsupportedOperationException - if this
collection does not support the addAll method. NullPointerException - if the
specified collection is null.See Also:add(Object)

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REMOVEALL

public boolean removeAll(Collection<?> c)

Removes from this collection all of its elements that are contained in the
specified collection (optional operation).

This implementation iterates over this collection, checking each element
returned by the iterator in turn to see if it's contained in the specified
collection. If it's so contained, it's removed from this collection with the
iterator's remove method.

Note that this implementation will throw an UnsupportedOperationException if the
iterator returned by the iterator method does not implement the remove method
and this collection contains one or more elements in common with the specified
collection.



Specified by:removeAll in interface Collection<E> Parameters:c - elements to be
removed from this collection. Returns:true if this collection changed as a
result of the call. Throws: UnsupportedOperationException - if the removeAll
method is not supported by this collection. NullPointerException - if the
specified collection is null.See Also:remove(Object), contains(Object)

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RETAINALL

public boolean retainAll(Collection<?> c)

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.

This implementation iterates over this collection, checking each element
returned by the iterator in turn to see if it's contained in the specified
collection. If it's not so contained, it's removed from this collection with the
iterator's remove method.

Note that this implementation will throw an UnsupportedOperationException if the
iterator returned by the iterator method does not implement the remove method
and this collection contains one or more elements not present in the specified
collection.



Specified by:retainAll in interface Collection<E> Parameters:c - elements to be
retained in this collection. Returns:true if this collection changed as a result
of the call. Throws: UnsupportedOperationException - if the retainAll method is
not supported by this Collection. NullPointerException - if the specified
collection is null.See Also:remove(Object), contains(Object)

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CLEAR

public void clear()

Removes all of the elements from this collection (optional operation). The
collection will be empty after this call returns (unless it throws an
exception).

This implementation iterates over this collection, removing each element using
the Iterator.remove operation. Most implementations will probably choose to
override this method for efficiency.

Note that this implementation will throw an UnsupportedOperationException if the
iterator returned by this collection's iterator method does not implement the
remove method and this collection is non-empty.



Specified by:clear in interface Collection<E> Throws:
UnsupportedOperationException - if the clear method is not supported by this
collection.

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TOSTRING

public String toString()

Returns a string representation of this collection. The string representation
consists of a list of the collection's elements in the order they are returned
by its iterator, enclosed in square brackets ("[]"). Adjacent elements are
separated by the characters ", " (comma and space). Elements are converted to
strings as by String.valueOf(Object).

This implementation creates an empty string buffer, appends a left square
bracket, and iterates over the collection appending the string representation of
each element in turn. After appending each element except the last, the string
", " is appended. Finally a right bracket is appended. A string is obtained from
the string buffer, and returned.



Overrides:toString in class Object Returns:a string representation of this
collection.

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Overview  Package   Class  Use  Tree  Deprecated  Index  Help 

JavaTM 2 Platform
Standard Ed. 5.0  PREV CLASS   NEXT CLASS FRAMES    NO FRAMES    All Classes All
Classes SUMMARY: NESTED | FIELD | CONSTR | METHOD
DETAIL: FIELD | CONSTR | METHOD

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Developer Documentation. That documentation contains more detailed,
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terms, workarounds, and working code examples.

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