java.util
public abstract class AbstractCollection<E> extends Object implements Collection<E>
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
Version: 1.24, 01/18/03
See Also: Collection
| 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. |
This implementation always throws an UnsupportedOperationException.
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.
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).
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
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.
Throws: UnsupportedOperationException if the clear method is not supported by this collection.
This implementation iterates over the elements in the collection, checking each element in turn for equality with the specified element.
Parameters: o object to be checked for containment in this collection.
Returns: true if this collection contains the specified element.
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.
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
This implementation returns size() == 0.
Returns: true if this collection contains no elements.
Returns: an iterator over the elements contained in this collection.
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.
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.
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.
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.
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.
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.
Returns: the number of elements in this collection.
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.
Returns: an array containing all of the elements in 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.
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.
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.
Returns: a string representation of this collection.