Quick Answer: When Should We Use Abstract Class?

Why should we use abstract class instead of normal class?

Abstract class basically allows us to provide default functionality for all the child classes through non-abstract methods.

So use abstract class instead of concrete class.

And when we try to create object of an abstract class user will get error on compilation instead of run-time.

So,it is safe to have abstract class..

What is difference between normal class and abstract class?

A concrete class can only have concrete methods. Even a single abstract method makes the class abstract. Abstract class can not be instantiated using new keyword. Concrete class can be instantiated using new keyword.

What is the purpose of abstract class?

The Purpose of Abstract Classes. The purpose of abstract classes is to function as base classes which can be extended by subclasses to create a full implementation. For instance, imagine that a certain process requires 3 steps: The step before the action.

What is meant by abstract class?

Abstract Classes and Methods Abstract class: is a restricted class that cannot be used to create objects (to access it, it must be inherited from another class). Abstract method: can only be used in an abstract class, and it does not have a body. The body is provided by the subclass (inherited from).

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 inherit 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.

Can we declare interface as abstract?

There is no point of declaring interface to be abstract. As the methods in the interface are abstract only.. One more thing abstract class can have both concrete and abstract methods but in the interface there should be only abstract methods.

Can we achieve abstraction without abstract class and interface?

How to achieve abstraction without using interfaces and abstract classes in java. … println is abstraction as we dont know detail behind it . Using factory classes is also abstraction as we dont know which subclass will be instantiated. Calling any method within an API is also abstraction.

What is meant by abstraction?

Abstraction (from the Latin abs, meaning away from and trahere , meaning to draw) is the process of taking away or removing characteristics from something in order to reduce it to a set of essential characteristics. … Abstraction is related to both encapsulation and data hiding.

What is an abstract class with example?

A class that is declared using “abstract” keyword is known as abstract class. 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.

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 we instantiate abstract class?

Abstract classes cannot be instantiated, but they can be subclassed. When an abstract class is subclassed, the subclass usually provides implementations for all of the abstract methods in its parent class. However, if it does not, then the subclass must also be declared abstract .

Why does an abstract class have a constructor?

Abstract classes require constructors to enforce a design contract using which objects can be initialized. Constructor can be used to setting up an attribute of the base class. This attribute will be available in subclass by inheritance. Before using this attribute, using the constructor it can be initialized.

Why do we need constructors inside abstract class?

Two reasons for this: 1) Abstract classes have constructors and those constructors are always invoked when a concrete subclass is instantiated. We know that when we are going to instantiate a class, we always use constructor of that class. … 2) We know constructor are also used to initialize fields of a class.

How do you use an abstract class?

Rules to RememberAbstract classes cannot be instantiated.If a class has at least one abstract method, then the class must be declared abstract.To use an abstract class, we must create a class that extends the abstract class (inheritance) and provide implementations for all abstract methods.More items…•

Can we replace interface with abstract class?

To answer your question, yes you could use an abstract class (providing no implementation) instead of an interface but I’d consider this bad practice: You’ve used up your “one-shot” at inheritance (without gaining any benefit). You cannot inherit from multiple abstract classes but you can implement multiple interfaces.

When would you use an interface?

Use interface when you want to exactly implement all the abstract methods to the class implementaing the interface and no default body to a method can be provided. It is considered good style to store a reference to a HashSet or TreeSet in a variable of type Set.

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.

What is abstract class in simple words?

An abstract class is a template definition of methods and variables of a class (category of objects) that contains one or more abstracted methods. … Declaring a class as abstract means that it cannot be directly instantiated, which means that an object cannot be created from it.

Can an abstract class have a constructor C++?

A class with one (or more) virtual pure functions is abstract, and it can’t be used to create a new object, so it doesn’t have a constructor.

What are the advantages of interface?

1) through interfaces we can implement multiple inheritance in java. 2) Interfaces function to break up the complex designs and clear the dependencies between objects. 3) Interfaces makes your application loosely coupled.