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L2.2 — Collections and Iterators covers the limitations of arrays, introduces ArrayList as a dynamic alternative (declaration, insertion, access, removal), explains generics for type safety, autoboxing/unboxing for primitives, and the Iterator pattern for decoupled collection traversal.

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📋 At a Glance

• [ ] Understand the four main problems with arrays (fixed size, painful insertion, index-only access, bounds exceptions)
• [ ] Know that ArrayList is a Java library class (not part of the language itself)
• [ ] Compare array vs ArrayList: declaration, insertion, access, removal
• [ ] Understand how ArrayLists are stored in memory vs arrays (linked nodes vs contiguous block)
• [ ] Use generics (ArrayList<Type>) to enforce type safety at compile time
• [ ] Understand why instanceof + typecasting is a last resort
• [ ] Know that collections can only store objects, not primitives
• [ ] Explain autoboxing (primitive to wrapper) and unboxing (wrapper to primitive)
• [ ] Use Iterator objects with hasNext() and next() to traverse collections
• [ ] Explain why iterators are useful (neater code, decoupling from collection)

1. Problems with Arrays

Arrays have four key limitations:

1. Fixed size — once created, the size cannot change
2. Painful insertion — adding new elements is difficult if you don't know how many exist already
3. Index-only access — you must use numeric indices to interact with elements
4. ArrayIndexOutOfBoundsException — accessing a nonexistent index causes a runtime error