AbstractCollection


  public
  
  
  abstract
  class
  AbstractCollection


  
    extends Object


  
  
      implements
      
        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 method 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.

Summary

Protected constructors

Public methods

Implementation Requirements:

Protected constructors
`AbstractCollection()` Sole constructor.

Public methods
`boolean`	`add(E e)` 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 all of this collection's elements that are also 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.
`<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.
`Object[]`	`toArray()` Returns an array containing all of the elements in this collection.
`String`	`toString()` Returns a string representation of this collection.

Parameters
`e`	`E`: element whose presence in this collection is to be ensured

Returns
`boolean`	`true` if this collection changed as a result of the call

Throws
`ClassCastException`
`IllegalArgumentException`
`IllegalStateException`
`NullPointerException`
`UnsupportedOperationException`

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

Implementation Requirements:

Parameters
`c`	`Collection`: collection containing elements to be added to this collection

Returns
`boolean`	`true` if this collection changed as a result of the call

Throws
`ClassCastException`
`IllegalArgumentException`
`IllegalStateException`
`NullPointerException`
`UnsupportedOperationException`

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.

Implementation Requirements:

Throws
`UnsupportedOperationException`

Parameters
`o`	`Object`: element whose presence in this collection is to be tested

Returns
`boolean`	`true` if this collection contains the specified element

Throws
`ClassCastException`
`NullPointerException`

Parameters
`c`	`Collection`: collection to be checked for containment in this collection

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

Throws
`ClassCastException`
`NullPointerException`

Returns
`boolean`	`true` if this collection contains no elements

Returns
`Iterator<E>`	an iterator over the elements contained in this collection

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.

Implementation Requirements:

Parameters
`o`	`Object`: element to be removed from this collection, if present

Returns
`boolean`	`true` if an element was removed as a result of this call

Throws
`ClassCastException`
`NullPointerException`
`UnsupportedOperationException`

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.

Implementation Requirements:

Parameters
`c`	`Collection`: collection containing elements to be removed from this collection

Returns
`boolean`	`true` if this collection changed as a result of the call

Throws
`ClassCastException`
`NullPointerException`
`UnsupportedOperationException`

Parameters
`c`	`Collection`: collection containing elements to be retained in this collection

Returns
`boolean`	`true` if this collection changed as a result of the call

Throws
`ClassCastException`
`NullPointerException`
`UnsupportedOperationException`

Returns
`int`	the number of elements in this collection

toArray

Added in API level 1

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

Implementation Requirements:

This implementation returns an array containing all the elements returned by this collection's iterator in the same order, stored in consecutive elements of the array, starting with index 0. If the number of elements returned by the iterator is too large to fit into the specified array, then the elements are returned in a newly allocated array with length equal to the number of elements returned by the iterator, even if the size of this collection changes during iteration, as might happen if the collection permits concurrent modification during iteration. The size method is called only as an optimization hint; the correct result is returned even if the iterator returns a different number of elements.
This method is equivalent to:
```
 List<E> list = new ArrayList<E>(size());
 for (E e : this)
     list.add(e);
 return list.toArray(a);
 
```

Parameters
`a`	`T`: the array into which the elements of this 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
`T[]`	an array containing all of the elements in this collection

Throws
`ArrayStoreException`
`NullPointerException`

AbstractSequentialList<E>	This class provides a skeletal implementation of the `List` interface to minimize the effort required to implement this interface backed by a "sequential access" data store (such as a linked list).
ArrayBlockingQueue<E>	A bounded blocking queue backed by an array.
ArrayList<E>	Resizable-array implementation of the `List` interface.
ConcurrentLinkedQueue<E>	An unbounded thread-safe queue based on linked nodes.
ConcurrentSkipListSet<E>	A scalable concurrent `NavigableSet` implementation based on a `ConcurrentSkipListMap`.
CopyOnWriteArraySet<E>	A `Set` that uses an internal `CopyOnWriteArrayList` for all of its operations.
DelayQueue<E extends Delayed>	An unbounded blocking queue of `Delayed` elements, in which an element generally becomes eligible for removal when its delay has expired.
EnumSet<E extends Enum<E>>	A specialized `Set` implementation for use with enum types.
HashSet<E>	This class implements the `Set` interface, backed by a hash table (actually a `HashMap` instance).
LinkedBlockingDeque<E>	An optionally-bounded blocking deque based on linked nodes.
LinkedBlockingQueue<E>	An optionally-bounded blocking queue based on linked nodes.
LinkedHashSet<E>	Hash table and linked list implementation of the `Set` interface, with well-defined encounter order.
LinkedList<E>	Doubly-linked list implementation of the `List` and `Deque` interfaces.
LinkedTransferQueue<E>	An unbounded `TransferQueue` based on linked nodes.
PriorityBlockingQueue<E>	An unbounded blocking queue that uses the same ordering rules as class `PriorityQueue` and supplies blocking retrieval operations.
PriorityQueue<E>	An unbounded priority queue based on a priority heap.
Stack<E>	The `Stack` class represents a last-in-first-out (LIFO) stack of objects.
SynchronousQueue<E>	A blocking queue in which each insert operation must wait for a corresponding remove operation by another thread, and vice versa.
TreeSet<E>	A `NavigableSet` implementation based on a `TreeMap`.
Vector<E>	The `Vector` class implements a growable array of objects.

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

AbstractCollection

Summary

Protected constructors

Public methods

Inherited methods

Protected constructors