Interfaces and abstract classes are both ways to define the behavior and structure of classes in object-oriented programming. While they have some similarities, there are also some key differences between the two.

– An interface is a collection of abstract methods that defines a contract for classes to implement.
– It specifies the methods that a class must implement, but does not provide any implementation details.
– A class can implement one or more interfaces, allowing it to take on multiple types or behaviors.
– Interfaces can also define constants and default methods with implementation, but they cannot have instance variables or constructors.
– Interfaces are used to achieve multiple inheritance in Java, as a class can implement multiple interfaces.
– Interfaces are often used to define common behavior among unrelated classes.

Abstract class:
– An abstract class is a class that cannot be instantiated, meaning you cannot create objects of the abstract class directly.
– It can have abstract methods, which are methods without implementation, as well as methods with implementation.
– Abstract classes can also have instance variables and constructors.
– A class can extend only one abstract class, as Java does not support multiple inheritance with abstract classes.
– Abstract classes are often used to define a base class with common behavior, but allow for specific behavior to be implemented by derived classes.

In summary, interfaces are used to define a contract that classes must implement, while abstract classes are used to provide a base class with common behavior. Interfaces define the methods that must be implemented, while abstract classes can provide some default implementation. Abstract classes can have instance variables and constructors, while interfaces cannot.