What are Abstract Classes in Java and How Do They Work?

Abstract Classes in Java: Understanding the Basics

Java introduces the concept of abstract classes as a powerful tool for abstraction and inheritance. An abstract class, unlike regular classes, cannot be instantiated directly but serves as a template for creating subclasses.

Defining and Implementing Abstract Classes

An abstract class is defined using the abstract keyword. It can have both abstract and non-abstract methods. Abstract methods do not have an implementation and must be overridden in subclasses. Non-abstract methods, however, have their implementations defined within the abstract class.

Inheritance from Abstract Classes

Subclasses created from an abstract class inherit its methods and can extend its functionality. They must implement all the abstract methods defined in the abstract class and can optionally override non-abstract methods.

Advantages of Abstract Classes

Code Reusability: Abstract classes promote code reusability by providing a common interface for subclasses to follow.

Enforcing Contract: Abstract methods enforce a contract that subclasses must adhere to, ensuring the presence of certain methods and behaviors.

Polymorphism: Abstract classes enable polymorphism, allowing subclasses with different implementations to be treated as the same abstract type.

Usage Scenarios

Abstract classes are commonly used in scenarios such as:

• Defining abstract data types (such as classes representing collections or data structures)
• Creating frameworks that provide a common interface for different implementations
• Implementing interfaces where multiple implementations can exist for the same functionality

Limitations of Abstract Classes

• Subclasses cannot extend multiple abstract classes (only one inheritance allowed).
• Abstract classes cannot be instantiated directly.
• Methods defined in an interface cannot be implemented.

The above is the detailed content of What are Abstract Classes in Java and How Do They Work?. For more information, please follow other related articles on the PHP Chinese website!