In object-oriented programming, "interface" (interface) and "abstract" (abstract class) are two important concepts used to implement code abstraction and encapsulation. They have different usage scenarios and differences in different situations.
Interface (Interface):
An interface is a specification that defines the method signatures that a class should have, but does not provide a specific implementation of the method. A class can implement one or more interfaces, which guarantees that these classes will implement the methods declared in the interface. Interfaces are often used in the following situations:
- Multiple inheritance problem: In some programming languages, a class can only inherit from a single parent class, but can implement multiple interfaces, so interfaces are a way to solve multiple inheritance problems.
- Code decoupling: Interfaces can separate method declarations from implementations, so that different classes can implement the same interface, thereby achieving loose coupling of code.
- Convention specification: An interface defines a set of methods, and after a class implements these methods, it means that it follows a certain convention and specification.
Abstract Class (abstract class):
An abstract class is a special type of class that can contain method declarations and concrete implementations. But unlike ordinary classes, an abstract class cannot be instantiated, it can only be inherited. Abstract classes are typically used in the following situations:
- Shared code: Abstract classes can contain some common method implementations, thus avoiding duplication of code. Subclasses can inherit these implementations and extend or override them as needed.
- Mandatory subclass implementation: An abstract class can define some abstract methods, which are not specifically implemented in the abstract class, but are left to subclasses to implement. This forces subclasses to provide concrete implementations of these methods.
- Partial abstract implementation: An abstract class can contain both concrete method implementations and some abstract methods, so that subclasses can be provided with some default implementations in the abstract class, and subclasses are also required to implement some specific methods.
the difference:
- Implementation method: Interfaces only contain method declarations without actual implementation code, while abstract classes can contain method declarations and implementations.
- Multiple inheritance: A class can implement multiple interfaces, but can only inherit from one abstract class (in general).
- Constructor: An interface cannot have a constructor, but an abstract class can.
- Fields: An interface cannot contain fields whereas an abstract class can contain fields.
- Instantiation: Interfaces cannot be instantiated, and abstract classes cannot be instantiated, but can only be inherited.
When choosing to use an interface or an abstract class, you need to consider your design goals. If you want to share the declaration of some methods between multiple classes, but the implementation can be different, you can use the interface. If you want to provide some default method implementations and require subclasses to implement certain methods, it may be more appropriate to use an abstract class. In some programming languages, the usage and characteristics of interfaces and abstract classes will also be different, and you need to choose according to the specifications of the specific language.