javautilVector

java.util.Vector is a legacy resizable array class in the Java platform. It implements the List interface and extends AbstractList, while also implementing RandomAccess, Cloneable, and Serializable. It stores its elements in an internal array and provides indexed access, insertion, and removal.

Vector is synchronized: most of its public methods are synchronized, making it thread-safe for simple concurrent use but potentially introducing contention and memory visibility costs. Because of this, Vector is generally considered a legacy collection, and ArrayList is preferred for non-synchronized use; for thread-safe behavior, alternatives such as Collections.synchronizedList(new ArrayList<>()) or concurrent collections may be better.

Public methods include those that were historically used in Vector-era code, such as addElement, insertElementAt, removeElementAt, elementAt, firstElement, lastElement, capacity, size, ensureCapacity, and trimToSize. In addition, Vector implements standard List methods like add, get, set, remove.

Constructors include Vector(), Vector(int initialCapacity), and Vector(int initialCapacity, int capacityIncrement). When capacityIncrement is zero, the vector grows by doubling its current capacity (newCapacity = oldCapacity * 2); if a nonzero capacityIncrement is supplied, growth is by that fixed amount.

It remains part of the Java standard library for compatibility, but in new code it is usually avoided in favor of ArrayList for a non-thread-safe dynamic array or a synchronized wrapper or concurrent collections for thread safety.

See also: java.util.List, ArrayList, Collections.synchronizedList, CopyOnWriteArrayList.