What is an abstract class in Java?
Table of Contents
Introduction
An abstract class in Java is a class that cannot be instantiated on its own and is designed to be subclassed. It may contain abstract methods—methods without an implementation—along with concrete methods that have a defined behavior. This feature supports Java's object-oriented programming principles by allowing for a more structured and reusable codebase.
Characteristics of Abstract Classes
1. Cannot Be Instantiated
An abstract class cannot create objects directly. It serves as a blueprint for other classes.
Example:
In this example, attempting to create an instance of Animal results in a compilation error.
2. Can Contain Abstract and Concrete Methods
An abstract class can have both abstract methods (without a body) and concrete methods (with a body). This allows it to provide common functionality while still enforcing a contract for subclasses.
Example:
In this example, Vehicle defines an abstract method start() and a concrete method stop(). The Car class implements the start() method.
3. Can Have Constructors
Abstract classes can have constructors, which can be called when an object of a subclass is created. This is useful for initializing fields.
Example:
In this example, the constructor of the abstract class Shape is called in the subclass Circle.
Conclusion
Abstract classes in Java provide a powerful way to define templates for other classes. They allow developers to create a common interface while still maintaining the flexibility to define specific behaviors in subclasses. By leveraging abstract classes, programmers can promote code reuse and maintainability in their Java applications.