Chapter 10 — Encapsulation, Inheritance, Polymorphism

Level: intermediate Estimated time: 7 h Prerequisites: Chapter 09 — Constructors and Modeling What you will be able to do by the end: protect a class's data with private members and validated getters and setters, build a class hierarchy with extends and super, override methods with @override, and write polymorphic code that handles Player, Enemy, and Boss the same way.

10.0 — Chapter Objectives

By the end of this chapter, you will be able to:

• name the three OOP pillars covered here;
• explain what encapsulation is in your own words;
• show concretely the danger of a public property that can be modified any which way;
• declare a private member with the _ prefix;
• explain that the scope of _ is the library (the file), not the class;
• write a getter that exposes a read-only value;
• write a setter that validates a value before accepting it;
• write private helper methods for internal use;
• build a fully encapsulated Player class, with lives always bounded between 0 and a maximum;
• explain what inheritance is and what it is for;
• use extends to create a subclass;
• say precisely what is inherited and what is not;
• call the parent constructor with super;
• call a parent method with super.methode();
• override an inherited method;
• use the @override annotation correctly;
• explain polymorphism using an example;
• iterate over a List<Character> containing Player and Enemy objects;
• use is and as to test and cast a type;
• build the Character → Player / Enemy / Boss hierarchy;
• recognize the situations where inheritance is a poor choice.