objects and classes

classes, constructors, inheritance, polymorphism, interfaces, and the contracts every object signs.

1. 01classes and objectsa class is a blueprint, new stamps out an object. what's actually in memory.
2. 02constructors and init orderthe exact order fields, initializers and constructors run in.
3. 03access controlprivate, package-private, protected, public. who can see what.
4. 04staticone copy per class vs one copy per object.
5. 05packages and importsfully qualified names, the classpath, and import module.
6. 06inheritanceextends, super, and how a subclass object is laid out in memory.
7. 07polymorphism and dynamic dispatchoverloading picks at compile time, overriding picks at runtime. the vtable.
8. 08abstract classes and interfacesdefault methods, the diamond problem, and when to use which.
9. 09equals, hashCode, toStringthe contracts every object signs, and what breaks when you don't keep them.
10. 10enumstype-safe constants that are secretly full classes.
11. 11nested and inner classesstatic nested, inner, local, anonymous. and the hidden this$0.
12. 12immutabilityfinal fields, defensive copies, and the aliasing bug that ruins your day.
13. 13composition over inheritancethe fragile base class problem, animated.