One of the most powerful programming languages is Java. It has the two most important things in the coding part. One is Abstract Class, and the other is Interface. These two are used in the coding area for declaring constructors and destructors. While declaring, they should follow some rules so that they can be placed correctly and the code will be executed without any errors.
Abstract Class vs Interface
The main difference between Abstract Class and Interface is that people use abstract classes for creating blueprints. The interface helps you to define functionality and not implementation. The keyword is compulsory in abstract class for declaring methods. But in the interface, keywords is not compulsory for declaring method. An abstract class can declare both construction and destructors. But interface can declare either a constructor or destructor.
An abstract class is used when it implements abstract methods and is inherited from another class. Proper implementation of abstract methods is very important whenever it inherits an abstract class. It is declared during abstract modifier. It is important because it gives a general idea about the problem. Once you get an idea, you will know the solution to the problem.
The interface is similar to protocols. It can contain constant declarations and method signatures. It uses a keyword called Interface for declaration. A class can implement any number of interfaces at a single time. An interface can extend to another interface. It is simple, like how a class extends another class. For all the lists of interfaces, you need to use commas to separate them.
Comparison Table Between Abstract Class and Interface
| Parameters of Comparison | Abstract Class | Interface |
| Usage of keyword | Abstract | Interface |
| Multiple Inheritance | It has no support for multiple inheritances. | The interface supports multiple inheritances. |
| Members | Private and protected | Public |
| Implementation | It will not implement the interface. | It will not implement the abstract class. |
| Access Modifier | It has an access modifier. | It has no access modifier. |
What is Abstract Class?
It can be subclassed but cannot be instantiated. It has two methods called abstract and non-abstract methods. It provides a blueprint for derived classes. They will set some rules for the derived class to implement whenever they inherit an abstract class. It is used for providing a common implementation for all the subclasses or for providing default implementation.
We can run it like any other class if it has the main method in it. It can implement interfaces without having the implementation of interface methods. This is used for making the code reusable and extendable. One simple example is, a vehicle is a parent class. It will have a truck and motorbike to be inherited from that vehicle class.
The best thing about the abstract class is you can declare fields that need not be static and final. You can define public, private, and protected methods. It has many abstract methods inside, which will be reused in the code later. It helps you to create functionality that can be used by the subclasses to implement or override. Many people prefer interface over an abstract class because you need not inherit the default behavior. And the other reason it has no support for multiple inheritances.
What is Interface?
It is a mechanism used for achieving abstraction. It is also used for achieving multiple inheritances in java. It has a set of specifications that should be implemented by other classes. With one single java class, we can implement multiple Java interfaces. Its methods are public and abstract. The main goal is to achieve total abstraction. Because Java does not support multiple inheritances by default. Users can achieve it only with the help of the interface.
Users use it for achieving loose coupling. In Java 8, the interface provides templates to users and helps to avoid dead diamond problems in multiple inheritances. It is similar to writing a class. It has behaviors that are implemented by the class. One single interface can extend multiple interfaces. The interface cannot be instantiated. You can only implement the interface and cannot extend the interface. All the methods that are available in the interface are considered to be abstract.
You need not write the abstract keyword while declaring an interface because it is simply abstract. In java 8, the interface can have default methods. In java, interfaces are divided into six types. Once a class implements an interface, all the non-default methods should also be implemented. The downside of the interface is you cannot have a constructor within an interface in java.
Main Differences Between Abstract Class and Interface
- The speed of the abstract class is fast. On the other hand, the speed of the interface is slow.
- An abstract class has data fields. On the other hand, the interface has no data fields.
- An abstract class is used to avoid independence. On the other hand, the interface is used for future enhancement.
- In an abstract class, you can define both fields and constants. On the other hand, in the interface, you cannot define any fields.
- An abstract class has an access modifier. On the other hand, the interface has no abstract modifier.
- The abstract class allows only one class to extend at a time. On the other hand, the interface allows extending any number of interfaces.
Conclusion
Both of them are used in the Java programming language, and they are important while writing the code. Learning about classes and interfaces can be really challenging in java. When properly handled, the code will be executed properly without any errors. In computer science, learning a programming language that is very much in use is important.
Java has now been spread into a big programming language. For Android development projects, many people prefer using java coding because it has all the standards, and the output will be clean when it is executed. Learning these two will help in getting the output well as they use constructors and destructors, which are very important when writing the code.
References
- https://link.springer.com/chapter/10.1007/978-1-4842-7322-7_2
- https://dl.acm.org/doi/abs/10.1145/1040305.1040314