Must-do problems: References, Casting and Immutability

120 min · Intermediate

Back to syllabus (References, Casting & Immutability)

Every problem here turns one idea of this module into a working program: a pattern instead of a blind cast, an object that can never change, a record that checks itself, or a nested class in the right place. Read the input with Scanner, keep classes small, and run every test before opening a hint.

What you will learn

Reach child-only members safely with instanceof patterns
Design immutable classes and records that validate once and never leak
Use immutability to keep versions and undo cheaply
Choose between static nested and inner classes in real designs

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