Iterable is the top-most interface in the Collection hierarchy.
It defines the iterator() method and is implemented by all collection classes.
Enables use of the enhanced for-each loop (for-each) in Java.
Collection extends Iterable and is the root interface for most data structures (excluding Map).
Collection has 3 main subinterfaces:
> List – Ordered, allows duplicates (e.g., ArrayList, LinkedList)
> Set – Unordered, no duplicates (e.g., HashSet, TreeSet)
> Queue – Typically FIFO (e.g., PriorityQueue, Deque)
Map is not a child of Collection; it's a separate interface that stores key-value pairs.
Common classes: HashMap, TreeMap, LinkedHashMap
Legacy Classes:
Vector, Stack, and Hashtable were introduced before Java 1.2
Synchronized but less preferred in modern development
Modern Alternatives:
Use ArrayList instead of Vector
Use Deque instead of Stack
Use ConcurrentHashMap instead of Hashtable for multithreaded use.
