Quick Answer: Can Abstract Class Be Empty?

Which is better abstract class or interface?

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..

Can abstract class have normal methods?

It can have abstract methods(methods without body) as well as concrete methods (regular methods with body). A normal class(non-abstract class) cannot have abstract methods. … An abstract class can not be instantiated, which means you are not allowed to create an object of it.

Can abstract class have constructor C++?

An abstract class can have constructor similar to normal class implementation. In the case of the destructor, we can declare a pure virtual destructor. It is important to have a destructor to delete the memory allocated for the class.

When should we use abstract class?

When to use an abstract classAn abstract class is a good choice if we are using the inheritance concept since it provides a common base class implementation to derived classes.An abstract class is also good if we want to declare non-public members. … If we want to add new methods in the future, then an abstract class is a better choice.More items…•

What is difference between interface and abstract class?

Main difference is methods of a Java interface are implicitly abstract and cannot have implementations. … Variables declared in a Java interface is by default final. An abstract class may contain non-final variables. Members of a Java interface are public by default.

Can abstract class have all concrete methods?

An abstract class is a class that is declared abstract – it may or may not include abstract methods. They cannot be instantiated so if you have an abstract class with concrete methods then it can be subclassed and the subclass can then be instantiated.

What is the benefit of making an empty abstract method in a base class?

It allows you to add abstract methods to your superclass (and implementations to the subclasses) later, without affecting any existing clients. The abstract keyword works even if the non-leaf class does not currently have any abstract methods. An abstract class can have abstract methods and “concrete” methods.

Can one abstract class extend another?

Abstract classes can implement one or more interfaces and can extend one abstract class at most. … Abstract classes can extend other at most one abstract or concrete class and implement several interfaces. Any class that does not implement all the abstract methods of it’s super class has to be an abstract class itself.

Can abstract class have body?

Abstract methods are declaration only and it will not have implementation. It will not have a method body. A Java class containing an abstract class must be declared as abstract class. An abstract method can only set a visibility modifier, one of public or protected.

Can an interface have a constructor?

No, you cannot have a constructor within an interface in Java. You can have only public, static, final variables and, public, abstract, methods as of Java7. From Java8 onwards interfaces allow default methods and static methods.

Can a single class inherit from multiple abstract classes?

Basically, the rule says that you can inherit from (extend) as many classes as you want, but if you do, only one of those classes can contain concrete (implemented) methods. … A class can extend at most one abstract class, but may implement many interfaces. That is, Java supports a limited form of multiple inheritance.

Can we inherit an abstract class?

Abstract Class But, if a class has at least one abstract method, then the class must be declared abstract. If a class is declared abstract, it cannot be instantiated. To use an abstract class, you have to inherit it from another class, provide implementations to the abstract methods in it.

Why can’t we instantiate an abstract class?

Because an abstract class is an incomplete class (incomplete in the sense it contains abstract methods without body and output) we cannot create an instance or object; the same way you say for an interface. You CAN instantiate an abstract class. You only need to provide a concrete subclass.

Can abstract class have constructor?

Yes! Abstract classes can have constructors! Yes, when we define a class to be an Abstract Class it cannot be instantiated but that does not mean an Abstract class cannot have a constructor. Each abstract class must have a concrete subclass which will implement the abstract methods of that abstract class.

Can we have abstract class without abstract method?

And yes, you can declare abstract class without defining an abstract method in it. … Once you declare a class abstract it indicates that the class is incomplete and, you cannot instantiate it. Hence, if you want to prevent instantiation of a class directly you can declare it abstract.