In Java, an abstract class is a class that cannot be instantiated on its own and is intended to be extended by subclasses. It can contain both concrete and abstract methods, and it can also have instance variables and constructors.
On the other hand, an interface is a type that defines a set of method signatures that a class can implement. Interfaces do not have instance variables, constructors or method implementations. The methods defined in an interface must be implemented by any class that implements the interface.
Here are some key differences between abstract classes and interfaces in Java:
Instantiation: An abstract class cannot be instantiated on its own, while an interface cannot be instantiated at all.
Method implementation: An abstract class can contain both concrete and abstract methods, while an interface can only contain method signatures without implementations.
Inheritance: A subclass can only extend one abstract class, while it can implement multiple interfaces.
Access modifiers: An abstract class can have constructors and non-public members, while an interface can only have public members.
Compatibility: If you add a new method to an interface, all classes that implement it must provide an implementation of the new method. With an abstract class, you can add new methods without breaking existing implementations, as long as you provide a default implementation.
In summary, while both abstract classes and interfaces are used to provide abstraction and define a contract for other classes to implement, abstract classes are more flexible and can contain both abstract and concrete methods, while interfaces only define method signatures without implementations.
