Abstract Classes

### Giai đoạn: Nền Tảng & Khái Niệm Cốt Lõi **Abstract Classes** An abstract class is a class that cannot be instantiated directly. Its primary purpose is to define a blueprint for other classes. It can contain abstract methods (methods without implementation) and concrete methods (methods with implementation). Subclasses must provide concrete implementations for all abstract methods inherited from the abstract class, unless the subclass is also declared abstract. This ensures that subclasses adhere to a specific interface or contract. ### Khái niệm cốt lõi: 1. **An abstract class is a class that cannot be instantiated directly** 2. **Its primary purpose is to define a blueprint for other classes** 3. **It can contain abstract methods (methods without implementation) and concrete methods (methods with implementation)** ### Tài liệu tham khảo chính thống: - [Abstract Classes](https://www.typescriptlang.org/docs/handbook/2/classes.html#abstract-classes-and-members) (official)