Topic 5. Classes and objects: properties, constructors, visibility modifiers, and packages

Goal: learn to create classes with validated constructors, properties, and methods; use encapsulation, packages, and UML to describe a model.

Lecture contents

1. Classes, constructors, and initialization — From separate variables to a model · Primary constructors and properties · Initializers and secondary constructors
2. Properties, accessors, and lateinit — Properties, accessors, and backing fields · Deferred assignment with lateinit
3. Visibility, packages, and nested classes — Visibility and responsibility boundaries · Packages, files, and imports · Nested and inner classes
4. UML and class contracts — UML and class testing · Reading the contract before writing code
5. Case studies and common mistakes — Lifecycle analysis: a step-by-step trace · Accessor visibility in practice

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