Summary

Conclusions

A class defines a validated way to create and change state. Constructors ensure consistent initial data, properties separate access from storage, and visibility modifiers restrict where changes can occur. Packages organize names; nested types express a local relationship. A model's quality is determined by its contract and checks, not by the number of classes written.

Self-check questions

1. Why does val not guarantee object immutability?
2. How does a constructor parameter differ from a property?
3. In what order do init and a secondary constructor execute?
4. Why must an initial value be checked separately from the setter?
5. When is field needed, and when is a field unnecessary?
6. What risk does reading an uninitialized lateinit create?
7. How does a module differ from a package?
8. When should a nested class be inner?
9. What should be checked after a method fails?
10. How will the class look in UML and to a Java client?