Most developers are familiar with the concept of abstract classes and interfaces. However, there is sometimes confusion about the differences between these two programming constructs. In this blog post, we will explore the key distinctions between abstract classes and interfaces. We will also discuss when it is appropriate to use each one.
What is Abstract Class?
An abstract class is a concept in object-oriented programming (OOP). An abstract class is used to provide a base for subclasses to inherit from. An abstract class cannot be instantiated. That means the Abstract class can have abstract methods (methods without body) and access modifiers for the Abstract methods. The abstract method is a method that is declared but not implemented in the Abstract class. When an Abstract class is subclassed, the subclass inherits all the non-static methods of the Abstract class. However, the subclass must implement the abstract methods of the Abstract class, or be itself declared as abstract. An Abstract class can have instance variables and concrete methods. The instance variables are inherited by subclasses, but the concrete methods are not. Concrete methods can be called from within an Abstract class or from subclasses that inherit from the Abstract class. An Abstract class can also have static methods and static variables. These members are inherited by subclasses and are accessible to them.
What is Interface?
Interface in java is a blueprint of a class. It is a collection of methods with empty bodies and constants which are public, static, and final by default. The interface is used to achieve abstraction where we can hide complex code from the user. The interface can have only abstract methods. A class that implements an interface must implement all the methods of the interface. The interface helps us to achieve multiple inheritances in java. The interface also represents the IS-A relationship. We can not instantiate an interface but we can instantiate a class that implements this interface. The interface plays an important role in the java programming language and is extensively used in android programming. The interface can not have a constructor because it is not a class. All the members of Interface are public by default. The interface is used to achieve abstraction and multiple inheritances in Java. The interface also represents the IS-A relationship and helps in loose coupling. The interface can not have a constructor because it is not a class but we can have static methods in Interface since Java 8 version.
Difference between Abstract Class and Interface
- An Abstract class is a class that contains at least one abstract method. An Abstract method is a method that is declared but not implemented in the code. Abstract classes can have both Abstract and Non-Abstract methods.
An Interface is 100% Abstract. It cannot contain any concrete(non-abstract) methods. All the methods in an Interface are public and abstract by default.
- An Abstract class can have fields and its own constructors, but an Interface cannot. Members of an Abstract class can access static fields and static methods whereas members of an Interface cannot.
- An Abstract class can extend another Abstract class or it can implement one or more Interfaces to achieve multiple inheritances. An Interface can extend to another Interface only.
- An Abstract class is fast because it supports dynamic binding for all non-static, non-private methods. An Interface is slow as compared to an Abstract because it supports dynamic binding only for those methods which are declared as public and final(in Java 8).
In conclusion, abstract classes and interfaces are both useful tools when creating object-oriented code. However, there are some key differences between the two that can help you decide which is best for your specific situation. Abstract classes provide more functionality and flexibility, while interfaces allow for easier testing and verification of type compatibility. Ultimately, the choice between using an abstract class or interface will depend on your individual coding needs and preferences.