Java OOP Knowledge Map Java OOP 知识地图
A practical map of the Java ideas you meet while reading and writing code: language basics, object-oriented design, modelling, contracts, exceptions, generics, collections, and testing. 这里不按课程编号整理，只按你写代码时真正会遇到的知识点拆开：Java 基础、面向对象设计、建模、契约、异常、泛型集合和单元测试。
Object-Oriented Design面向对象设计
Start from class/object, then connect inheritance, has-a, method forwarding, abstract classes, interfaces, overriding, overloading, and polymorphism. 从 class/object 开始，理解 inheritance、has-a、method forwarding、abstract class、interface、overriding、overloading 和 polymorphism。
Java BasicsJava 基础知识
Match everyday Java code with the right names: JVM, bytecode, class, field, method, constructor, this, super, and private. 把你会用但叫不出名字的东西对上术语：JVM、bytecode、class、field、method、constructor、this、super、private。
Theory Quiz理论测验
40 questions from easy to hard, focused on theory and design judgement. 40 道题，从简单到难，主要考理论和设计判断，帮助吃透知识点。
Supporting Topics 后续知识点
Domain Modelling
Turn nouns and verbs in requirements into classes, relationships, behaviours, and UML-style structure.从需求文字里找 noun/verb，把真实世界概念变成 class、relationship 和 UML 结构。
Design by Contract
Use preconditions, postconditions, and invariants to make responsibility boundaries explicit.用 precondition、postcondition、invariant 讲清楚“谁负责保证什么”。
Exceptions
Understand throw, catch, finally, checked exceptions, and unchecked exceptions.理解 throw、catch、finally，以及 checked exception 和 unchecked exception 的使用场景。
Generics & Collections
Read List<String>, Map<K,V>, T/E/K/V, and why generics reduce unsafe casts.看懂 List<String>、Map<K,V>、T/E/K/V，以及为什么泛型能减少 cast。
JUnit Testing
Connect unit tests, test cases, assertions, test suites, and refactoring safety.把 unit test、test case、assert、test suite 和 refactoring 的关系讲清楚。