List Interface

List is an ordered collection that:

• allows duplicates,
• maintains insertion order,
• supports index-based access.

It extends the Collection interface.

Common Implementations

Implementation	Features
ArrayList	Fast reads, resizable array, slow inserts/removes
LinkedList	Fast inserts/removes, slower random access
Vector	Like ArrayList but synchronized (legacy)
Stack	LIFO (extends Vector)

Example

List<String> names = new ArrayList<>();
names.add("Kamil");
names.add("Kamil"); // duplicates allowed
System.out.println(names.get(0)); // Kamil

Methods

list.add("A");
list.get(0);
list.set(0, "B");
list.remove(0);
list.contains("B");
list.size();
list.clear();

Comparison

ArrayList vs LinkedList

Feature	ArrayList	LinkedList
Backed By	Dynamic array	Doubly-linked list
Access Time	Fast (O(1))	Slower (O(n)
Insert/Delete	Slower (Shifts)	Faster (O(1) if at ends)
Memory	Compact	More (due to nodes)

Use Cases

• ArrayList: fast access, read-heady apps.
• LinkedList: frequent insert/delete (e.g. queues).
• Vector: thread-safe legacy code (avoid unless needed).
• Stack: LIFO operations (use Deque instead in modern code).

Tip

Be ready to explain:

• compare ArrayList vs LinkedList,
• show time complexity awareness,
• explain why List allows duplicates and index access.

---

Parent: _Collections