What is the difference between abstract classes and interfaces in Java?

In Java, the main difference between abstract classes and interfaces lies in their implementation and usage. An abstract class is a class that cannot be instantiated and may contain abstract methods, which must be implemented by its subclasses. On the other hand, an interface in Java is a reference type similar to a class, which can contain only abstract methods, default methods, static methods, and constants.

The key focus keyword in this context is "difference between abstract classes and interfaces." Abstract classes can have both abstract and concrete methods, while interfaces can only have abstract methods. Subclasses can extend only a single abstract class, but they can implement multiple interfaces.

Overall, abstract classes provide a way to share code and enforce a specific structure, while interfaces allow for multiple inheritance and define a contract for classes to implement certain behaviors.