Difference between abstract class and interface

Difference between Abstract Class and Interface is one of the popular interview questions. Abstract Class and Interface are a core part of the Java programming language. Whether to choose an interface or abstract class is a design decision that every architect faces. In my last articles, I have provided as much as possible details about • 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. • Subclasses use extends keyword to extend an abstract class and they need to provide implementation of all the declared methods in the abstract class unless the subclass is also an abstract class whereas subclasses use implements keyword to implement interfaces and should provide implementation for all the methods declared in the interface. • Abstract classes can have methods with implementation whereas interface provides absolute abstraction and can’t have any method implementations. Note that from Java 8 onwards, we can create default and static methods in interface that contains the method implementations. • Abstract classes can have constructors but interfaces can’t have constructors. • Abstract class have all the features of a normal java class except that we can’t instantiate it. We can use abstract keyword to make a class abstract but interfaces are a completely different type and can have only public static final constants and method declarations. • Abst...

Introduction This is now an important question asked by an interviewer in the interview. I have found many solutions on the Internet regarding " When to use interface and abstract method?". Lately, I thought about writing an article on simplifying my experience and what I learned. If you check both the things, they seem to be very similar, which makes a confusion in the mind while answering these questions. Here, in this article, I will try to explain these things. Abstract Class Before giving the introduction about abstract class, I will try to explain the abstract method, first. Abstract Method A method without any particular body is known as an abstract method. These methods contain only declaration of the method.To declare an abstract method, we have to use abstract modifier on the method.The class, under which these abstract methods are defined, is referred to as an abstract class, and this also has to be declared using abstract modifier.The implementation of abstract method is done by a derived class. When the abstract class inherits the derived class, the derived class must implement the abstract methods using override keyword in it. Abstract ClassAn abstract class is a special class that contains both abstract and non-abstract members in it. Example public abstract class Cars Thus, it resolves the demerits of all the above 3 cases. So, in this situation, we have to use Interface. Here, I have shown you the sketch diagram. In this way, we can use abstract class and...

As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, • abstract class Should be used when there is a IS-A relationship and no instances should be allowed to be created from that abstract class. Example: An Animal is an abstract base class where specific animals can be derived from, i.e. Horse, Pig etc. By making Animal abstract it is not allowed to create an Animal instance. • interface An interface should be used to implement functionality in a class. Suppose we want a horse to be able to Jump, an interface IJumping can be created. By adding this interface to Horse, all methods in IJumping should be implemented. In IJumping itself only the declarations (e.g. StartJump and EndJump are defined), in Horse the implementations of these two methods should be added. • sealed class By making Horse sealed, it is not possible to inherit from it, e.g. making classes like Pony or WorkHorse which you like to be inheriting from Horse. • static class Mostly used for 'utility' functions. Suppose you need some method to calculate the average of some numbers to be used in the Horse class, but you don't want to put that in Horse since it is unrelated and it also is not related to animals, you can create a class to have this kind of methods. Y...

Recently I have started to wrap my head around OOP, and I am now to the point where the more I read about the differences between abstract classes and interfaces the more confused I become. So far, neither can be instantiated. Interfaces are more or less structural blueprints that determine the skeleton and abstracts are different by being able to partially implement code. I would like to learn more about these through my specific situation. Here is a link to my first question if you would like a little more background information: Here are two classes I created: class Ad Or would I use an interface and, because these are so similar, create a structure that each of the subclasses are forced to use for integrity reasons, and leave it up to the end developer who fleshes out that class to be responsible for each of the details of even the common functions. my thinking there is that some 'common' functions may need to be tweaked in the future for the needs of their specific class. Despite all that above, if you believe I am misunderstanding the what and the why of abstract classes and interfaces altogether, by all means let a valid answer to be stop thinking in this direction and suggest the proper way to move forward! Thanks! In layman's terms: Interfaces are for "can do/can be treated as" type of relationships. Abstract ( as well as concrete ) classes are for "is a" kind of relationship. Look at these examples: class Bird extends Animal implements Flight; class Plane extend...

In this article, we are going to see the difference between abstract classes and interface in • What is an • What is an • Difference between abstract class and interface in Python What is an Abstract class in Python? A blueprint for other classes might be thought of as an abstract class. You may use it to define a collection of methods that are required for all subclasses derived from the abstract class. An abstract class is one that includes one or more abstract methods. A method that has a declaration but no implementation is said to be abstract. We use an abstract class for creating huge functional units. An abstract class is used to offer a standard interface for various implementations of a component. Example: Python does not come with any abstract classes by default. Python has a module called ABC that serves as the foundation for building Abstract Base Classes (ABC). ABC works by decorating methods of the base class as abstract and then registering concrete classes as implementations of the abstract base.When a method is decorated with the keyword@abstractmethod, it becomes abstract. Output: I can walk and run I can crawl I can bark I can roar What is an Interface in Python? The interface in object-oriented languages like Python is a set of method signatures that the implementing class is expected to provide. Writing ordered code and achieving abstraction are both possible through interface implementation. Example: Python “object interfaces” are implemented in the m...

Abstract classes and interfaces are the two main building blocks of the Topics discussed in this article are as follows: • • • • To understand the differences between abstract class and interface in What is Abstract Class in Java? In any programming language, Note: An abstract method, is a method which is not implemented in place and adds incompleteness to package MyPackage; //abstract class abstract class Animal Output Humans leave on land and respire through lungs or trachea. Fishes leave in water and respire through gills or their skin. If you do not have any common code between your From the above content, you might have noticed the key difference between abstract class and interface in Abstract Class vs Interface The table below lists out the key differences between abstract class and interface. Parameter Abstract Class Interface Default Method Implementation It can have default method implementation Interfaces provide pure abstraction & can not have implementation at all Variables It may contain non-final variables. Variables declared in an interface are by default final Keyword Used An abstract class can be extended using the keyword “extends The interface should be implemented using keyword ïmplements Access Modifiers Can have public, protected, private and default modifier Interface methods are by default public. you can not use any other access modifier with it Speed of Implementation It is faster than the interface An Interface is somewhat slower & require extra...

In this article, we are going to see the difference between abstract classes and interface in • What is an • What is an • Difference between abstract class and interface in Python What is an Abstract class in Python? A blueprint for other classes might be thought of as an abstract class. You may use it to define a collection of methods that are required for all subclasses derived from the abstract class. An abstract class is one that includes one or more abstract methods. A method that has a declaration but no implementation is said to be abstract. We use an abstract class for creating huge functional units. An abstract class is used to offer a standard interface for various implementations of a component. Example: Python does not come with any abstract classes by default. Python has a module called ABC that serves as the foundation for building Abstract Base Classes (ABC). ABC works by decorating methods of the base class as abstract and then registering concrete classes as implementations of the abstract base.When a method is decorated with the keyword@abstractmethod, it becomes abstract. Output: I can walk and run I can crawl I can bark I can roar What is an Interface in Python? The interface in object-oriented languages like Python is a set of method signatures that the implementing class is expected to provide. Writing ordered code and achieving abstraction are both possible through interface implementation. Example: Python “object interfaces” are implemented in the m...

As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, • abstract class Should be used when there is a IS-A relationship and no instances should be allowed to be created from that abstract class. Example: An Animal is an abstract base class where specific animals can be derived from, i.e. Horse, Pig etc. By making Animal abstract it is not allowed to create an Animal instance. • interface An interface should be used to implement functionality in a class. Suppose we want a horse to be able to Jump, an interface IJumping can be created. By adding this interface to Horse, all methods in IJumping should be implemented. In IJumping itself only the declarations (e.g. StartJump and EndJump are defined), in Horse the implementations of these two methods should be added. • sealed class By making Horse sealed, it is not possible to inherit from it, e.g. making classes like Pony or WorkHorse which you like to be inheriting from Horse. • static class Mostly used for 'utility' functions. Suppose you need some method to calculate the average of some numbers to be used in the Horse class, but you don't want to put that in Horse since it is unrelated and it also is not related to animals, you can create a class to have this kind of methods. Y...

Abstract classes and interfaces are the two main building blocks of the Topics discussed in this article are as follows: • • • • To understand the differences between abstract class and interface in What is Abstract Class in Java? In any programming language, Note: An abstract method, is a method which is not implemented in place and adds incompleteness to package MyPackage; //abstract class abstract class Animal Output Humans leave on land and respire through lungs or trachea. Fishes leave in water and respire through gills or their skin. If you do not have any common code between your From the above content, you might have noticed the key difference between abstract class and interface in Abstract Class vs Interface The table below lists out the key differences between abstract class and interface. Parameter Abstract Class Interface Default Method Implementation It can have default method implementation Interfaces provide pure abstraction & can not have implementation at all Variables It may contain non-final variables. Variables declared in an interface are by default final Keyword Used An abstract class can be extended using the keyword “extends The interface should be implemented using keyword ïmplements Access Modifiers Can have public, protected, private and default modifier Interface methods are by default public. you can not use any other access modifier with it Speed of Implementation It is faster than the interface An Interface is somewhat slower & require extra...

Recently I have started to wrap my head around OOP, and I am now to the point where the more I read about the differences between abstract classes and interfaces the more confused I become. So far, neither can be instantiated. Interfaces are more or less structural blueprints that determine the skeleton and abstracts are different by being able to partially implement code. I would like to learn more about these through my specific situation. Here is a link to my first question if you would like a little more background information: Here are two classes I created: class Ad Or would I use an interface and, because these are so similar, create a structure that each of the subclasses are forced to use for integrity reasons, and leave it up to the end developer who fleshes out that class to be responsible for each of the details of even the common functions. my thinking there is that some 'common' functions may need to be tweaked in the future for the needs of their specific class. Despite all that above, if you believe I am misunderstanding the what and the why of abstract classes and interfaces altogether, by all means let a valid answer to be stop thinking in this direction and suggest the proper way to move forward! Thanks! In layman's terms: Interfaces are for "can do/can be treated as" type of relationships. Abstract ( as well as concrete ) classes are for "is a" kind of relationship. Look at these examples: class Bird extends Animal implements Flight; class Plane extend...