Introduction- Srini

The Java Collections Framework provides a unified structure for working with groups of objects. At its core is the Collection interface, which defines common behaviors for all standard collections.

Since Collection extends Iterable, all collections can be looped through using a for-each loop. As an interface, Collection doesn't hold data—it defines a contract that classes like ArrayList, HashSet, and LinkedList follow.

Key Benefits of Using Collections

  • Dynamic sizing (unlike arrays)
  • Works with any object type using generics
  • Common operations like add, remove, and contains
  • Allows flexible, reusable code through interfaces

Core Java Collection Implementations

  • ArrayList
    • Implements: List (which extends Collection)
    • Behavior: Ordered, allows duplicates, fast random access
    • Example: ArrayList
  • HashSet
    • Implements: Set (which extends Collection)
    • Behavior: Unordered, no duplicates, fast operations using hashing
    • Example: HashSet
  • LinkedList
    • Implements: List, Deque, Queue (all extend Collection)
    • Behavior: Ordered, allows duplicates, efficient insert/remove
    • Example: LinkedList