javautilList

java.util.List is a central interface in the Java Collections Framework that represents an ordered collection (a sequence) of elements. It allows duplicate elements and preserves insertion order. Each element is accessible by a zero-based index, and operations commonly rely on that index, such as retrieval, insertion, and removal.

The interface is generic, declared as List<E>, and extends Collection<E>. It inherits standard collection operations and adds list-specific methods, including get(int index), set(int index, E element), add(E element), add(int index, E element), remove(int index), remove(Object o), indexOf(Object o), lastIndexOf(Object o), size(), isEmpty(), and subList(int fromIndex, int toIndex). It also supports iteration via the ListIterator<E>.

Common implementations include ArrayList, LinkedList, Vector, and specialized forms like CopyOnWriteArrayList. ArrayList provides fast random access with O(1) time for get and set, but may incur O(n) time for inserts or removals in the middle. LinkedList offers efficient insertions and removals at arbitrary positions but slower indexed access. Vector is a synchronized legacy implementation, while CopyOnWriteArrayList focuses on concurrent use with different performance characteristics. Some lists related to fixed-size arrays (such as those returned by Arrays.asList) have restricted mutability.

Additional notes: a List may be converted to arrays via toArray methods, can be sorted with Collections.sort or List.sort, and can be streamed or collected in various ways. Most List implementations are not thread-safe, requiring synchronization or concurrent alternatives for multi-threaded use. In Java 9 and later, immutable lists can be created with List.of, while Collections.unmodifiableList provides a read-only view.