Topic 7. Data classes, enums, sealed classes, singleton objects, and companion objects

Goal: model values, fixed sets, and states with data, enum, sealed, object, and companion object; test copying, exhaustiveness, and controlled creation.

Lecture contents

1. Data classes and copying — Choosing a model form by its meaning · Data classes and generated operations · Immutability and shallow copying
2. Enums and sealed hierarchies — An enum: a fixed set of constants · Sealed hierarchies and variant-specific data
3. Singleton objects and companions — Object: one accessible instance · Companion object and factory methods · An anonymous object as a local implementation
4. Choosing a model and common mistakes — Model selection matrix · Checks and common mistakes · Behavior of individual enum constants

Practice and review

• Practice — 3 worked examples with complete code
• Tasks — 30 variants, each with tasks at three difficulty levels
• Summary — conclusions and self-check questions