implements List<E> RandomAccess Cloneable Serializable
Resizable-array implementation of the List interface. Implements all optional list operations, and permits all elements, including null. In addition to implementing the List interface, this class provides methods to manipulate the size of the array that is used internally to store the list. (This class is roughly equivalent to Vector, except that it is unsynchronized.)
The size, isEmpty, get, set, iterator, and listIterator operations run in constant time. The add operation runs in amortized constant time, that is, adding n elements requires O(n) time. All of the other operations run in linear time (roughly speaking). The constant factor is low compared to that for the LinkedList implementation.
Each ArrayList instance has a capacity. The capacity is the size of the array used to store the elements in the list. It is always at least as large as the list size. As elements are added to an ArrayList, its capacity grows automatically. The details of the growth policy are not specified beyond the fact that adding an element has constant amortized time cost.
An application can increase the capacity of an ArrayList instance before adding a large number of elements using the ensureCapacity operation. This may reduce the amount of incremental reallocation.
Note that this implementation is not synchronized.
If multiple threads access an ArrayList instance concurrently,
and at least one of the threads modifies the list structurally, it
must be synchronized externally. (A structural modification is
any operation that adds or deletes one or more elements, or explicitly
resizes the backing array; merely setting the value of an element is not
a structural modification.) This is typically accomplished by
synchronizing on some object that naturally encapsulates the list.
If no such object exists, the list should be "wrapped" using the
method. This is best done at creation time, to prevent accidental
unsynchronized access to the list:
List list = Collections.synchronizedList(new ArrayList(...));
The iterators returned by this class's
listIterator methods are fail-fast:
if the list is structurally modified at any time after the iterator is
created, in any way except through the iterator's own
add methods, the iterator will throw a
ConcurrentModificationException. Thus, in the face of
concurrent modification, the iterator fails quickly and cleanly, rather
than risking arbitrary, non-deterministic behavior at an undetermined
time in the future.
Note that the fail-fast behavior of an iterator cannot be guaranteed
as it is, generally speaking, impossible to make any hard guarantees in the
presence of unsynchronized concurrent modification. Fail-fast iterators
ConcurrentModificationException on a best-effort basis.
Therefore, it would be wrong to write a program that depended on this
exception for its correctness: the fail-fast behavior of iterators
should be used only to detect bugs.
This class is a member of the Java Collections Framework.
Inherited Field Summary
Public Constructor Summary
Constructs an empty list with the specified initial capacity.
Constructs an empty list with an initial capacity of ten.
Public Method Summary
Appends the specified element to the end of this list.
add(int index, E element)
Inserts the specified element at the specified position in this list.
Removes all of the elements from this list.
Returns a shallow copy of this ArrayList instance.
Increases the capacity of this ArrayList instance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument.
Returns the element at the specified position in this list.
Returns true if this list contains no elements.
Returns an iterator over the elements in this list in proper sequence.
Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list.
Returns a list iterator over the elements in this list (in proper sequence).
Removes the element at the specified position in this list.
set(int index, E element)
Replaces the element at the specified position in this list with the specified element.
Returns the number of elements in this list.
subList(int fromIndex, int toIndex)
Returns a view of the portion of this list between the specified
Returns an array containing all of the elements in this list in proper sequence (from first to last element).