What is the use of abstract class in Java?

Asked By: Annabell Koutsoubos | Last Updated: 3rd March, 2020
Category: technology and computing programming languages
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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. We can run abstract class in java like any other class if it has main() method.

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Hereof, what is the purpose of abstract class in Java?

A Java abstract class is a class which cannot be instantiated, meaning you cannot create new instances of an abstract class. The purpose of an abstract class is to function as a base for subclasses.

Secondly, what is abstract class in Java 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). An abstract class can not be instantiated, which means you are not allowed to create an object of it.

Similarly, you may ask, what is the use of interface and abstract class in Java?

An abstract class permits you to make functionality that subclasses can implement or override whereas an interface only permits you to state functionality but not to implement it. A class can extend only one abstract class while a class can implement multiple interfaces.

Where do we use interface and abstract class in Java?

abstract keyword is used to create an abstract class and it can be used with methods also whereas interface keyword is used to create interface and it can't be used with methods. Abstract classes can extend other class and implement interfaces but interface can only extend other interfaces.

38 Related Question Answers Found

What is the purpose of abstract?

An abstract is a brief summary of a research article, thesis, review, conference proceeding, or any in-depth analysis of a particular subject and is often used to help the reader quickly ascertain the paper's purpose.

Can an abstract class have a constructor?

Yes, an abstract class can have a constructor in Java. You can either explicitly provide a constructor to abstract class or if you don't, the compiler will add default constructor of no argument in abstract class. In order to use an abstract class in Java, You need to extend it and provide a concrete class.

Why is abstraction so important?

Abstraction is one of the key elements of good software design. It helps encapsulate behavior. It helps decouple software elements. When developing with higher level of abstraction, you communicate the behavior and less the implementation.

Can I create object of 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.

What is abstract class in OOP?


An abstract class is a template definition of methods and variables of a class (category of objects) that contains one or more abstracted methods. Abstract classes are used in all object-oriented programming (OOP) languages, including Java (see Java abstract class), C++, C# and VB.NET.

What is an interface?

In computing, an interface is a shared boundary across which two or more separate components of a computer system exchange information. The exchange can be between software, computer hardware, peripheral devices, humans, and combinations of these.

Can you inherit from an abstract class Java?

Abstract Class
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. If you inherit an abstract class, you have to provide implementations to all the abstract methods in it.

Can abstract class have private methods?

Abstract methods in an abstract class cannot be private but can be of specifiers public, protected or default. When a method is private, the sub classes can't access it, hence they can't override it. An abstract method cannot be private and also cannot be static, final, native, strictfp, or synchronized.

Why do we need interface?

interface allows a class to behave like multiple types, which is not possible without multiple inheritance of class. It also ensures that you follow programming to interface than implementation pattern, which eventually adds lot of flexibility in your system.

Which is better abstract class or interface?


You can only have one direct abstract superclass. Therefore, interfaces are useful if you need to expose two or more interfaces. 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.

What is oops concept?

OOP concepts in Java are the main ideas behind Java's Object Oriented Programming. They are an abstraction, encapsulation, inheritance, and polymorphism. Basically, Java OOP concepts let us create working methods and variables, then re-use all or part of them without compromising security.

What is difference between abstract and interface?

Main difference is methods of a Java interface are implicitly abstract and cannot have implementations. A Java abstract class can have instance methods that implements a default behavior. A Java class can implement multiple interfaces but it can extend only one abstract class.

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.

Can a non abstract class implement an interface?

Interfaces can not extend a class or implement an Interface. An interface can extend another Interface. A non-abstract class which is implementing an Interface needs to follow some rules. This class needs to provide the concrete implementation of all abstract method.

Why do we need interface and abstract 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 do you mean 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 class and interface?

A class describes the attributes and behaviors of an object. An interface contains behaviors that a class implements. A class may contain abstract methods, concrete methods. An interface contains only abstract methods. Members of a class can be public, private, protected or default.