In which of these situations are interfaces better than abstract classes?

An interface is better than a abstract class when you want multiple classes to implement that interface and when you don’t have to inherit default behavior. In order to provide WebServices or do JMock tests you dont need the actual implementation, you just need an interface definition.

Should an abstract class implement an interface?

Java Abstract class can implement interfaces without even providing the implementation of interface methods. Java Abstract class is used to provide common method implementation to all the subclasses or to provide default implementation.

When should I use an interface and when should I use a base class?

My rule of thumb: If you want to provide some common functionality accessible to a subset of classes, use a base class. If you want to define the expected behavior of of a subset of classes, use an interface.

What is the advantage of interface over abstract class in Java?

The main advantages of interface over abstract class is to overcome the occurrence of diamond problem and achieve multiple inheritance. In java there is no solution provided for diamond problem using classes. For this reason multiple inheritance is block using classes in java.

Can abstract class inherit from interface?

An abstract class can inherit a class and multiple interfaces. An interface cannot declare constructors or destructors. An abstract class can declare constructors and destructors. It can extend any number of interfaces.

When would we use an interface over a parent class?

The short answer: An abstract class allows you to create functionality that subclasses can implement or override. An interface only allows you to define functionality, not implement it. And whereas a class can extend only one abstract class, it can take advantage of multiple interfaces.

What is the purpose of interfaces?

The purpose of interfaces is to allow the computer to enforce these properties and to know that an object of TYPE T (whatever the interface is ) must have functions called X,Y,Z, etc.

What is the difference between interface and abstract class?

The key technical differences between an abstract class and an interface are: Abstract classes can have constants, members, method stubs (methods without a body) and defined methods, whereas interfaces can only have constants and methods stubs.

What is the advantage of interface over abstract classes?

An interface can be used to define a contract behavior and it can also act as a contract between two systems to interact while an abstract class is mainly used to define default behavior for subclasses, it means that all child classes should have performed the same functionality.

Can you implement an interface in abstract class?

In Java, an abstract class can implement an interface , and not provide implementations of all of the interface’s methods. It is the responsibility of the first concrete class that has that abstract class as an ancestor to implement all of the methods in the interface.

When do we go for abstract and interface?

If the functionality you are creating will be useful across a wide range of disparate objects, use an interface. Abstract classes should be used primarily for objects that are closely related, whereas interfaces are best suited for providing common functionality to unrelated classes.