Abstract Classes vs Interfaces in Java - Explanation and Usage

When writing Java code, understanding the difference between abstract classes and interfaces is crucial. Both serve as blueprints for classes to implement, but they have distinct characteristics.

Abstract Classes:

• Abstract classes can contain both concrete methods and abstract methods.
• They can have instance variables.
• They cannot instantiate objects, meaning you cannot create an instance of an abstract class.
• Can provide a partial implementation, allowing subclasses to extend them further.
• Use the keyword abstract to define an abstract class.

Interfaces:

• Interfaces can only contain abstract methods and constants.
• They cannot have instance variables.
• Classes can implement multiple interfaces but can only inherit from one class.
• Provide a way for classes to adhere to a contract without specifying the implementation.
• Use the keyword interface to define an interface in Java.

When to Choose Abstract Classes or Interfaces:

Choosing between abstract classes and interfaces depends on the specific requirements of your code. Use abstract classes when you want to provide a partial implementation and have common functionality to share among subclasses. Interfaces are suitable when you want to define a contract that multiple classes can adhere to without specifying the implementation details.

Overall, the decision to use abstract classes or interfaces in Java should align with the design principles and structure of your project.