Understanding the Difference between Abstract Class and Interface in Object-Oriented Programming
Object-Oriented Programming (OOP) is a popular programming paradigm that is widely used in software development. In OOP, two important concepts are abstract class and interface, both of which are used to define classes and methods. However, many people get confused between these two concepts. Let’s look at the difference between abstract class and interface in detail.
What is an Abstract Class?
An abstract class is a class that cannot be instantiated. In other words, you cannot create an object or instance of an abstract class. Instead, it is used as a base or parent class for other classes. An abstract class defines a set of abstract methods that must be implemented by its child classes. Abstract classes can also contain concrete or non-abstract methods, fields, and properties.
What is an Interface?
An interface is a contract that specifies a set of methods that must be implemented by a class. An interface is similar to an abstract class in that it defines methods without providing their implementation. However, an interface cannot have any fields or properties, and all methods in an interface are implicitly abstract. A class can implement multiple interfaces but can only inherit from a single abstract class.
Key Differences
One of the main differences between an abstract class and interface is that an abstract class can contain both abstract and concrete methods, while an interface can only contain abstract methods. Another significant difference is that you cannot create an instance of an abstract class, but you can create an instance of a class that implements an interface.
Another difference is that an abstract class can provide a default implementation for the methods it defines, while an interface cannot provide any implementation. Additionally, a class that inherits from an abstract class can modify the behavior of its parent class methods, but a class that implements an interface must implement all the methods specified in the interface.
Which One to Use?
Choosing between an abstract class and an interface depends on your requirements. If you need to define a base class that provides some default behavior, you should use an abstract class. On the other hand, if you need to define a contract specifying a set of methods that a class must implement, you should use an interface.
In conclusion, an abstract class and an interface are both important concepts in OOP. While they may seem similar, they have some key differences that should be carefully understood before deciding which one to use. Proper understanding and usage of these concepts will lead to well-designed and efficient software systems.
Table difference between abstract class and interface
| Abstract Class | Interface |
|---|---|
| Can have instance variables and non-abstract methods. | Cannot have instance variables and non-abstract methods. Only contains method signatures. |
| Can have constructors. | Cannot have constructors. |
| Can have access modifiers for their methods and variables. | All methods and variables are public by default. |
| Can be extended by one class and multiple interfaces. | Can be implemented by multiple classes. |
| Used when creating a base class for other classes to extend from. | Used to define common behavior for unrelated classes. |