Need for Abstract Classes and Interfaces in Java

What is Abstraction?

The definition of data abstraction can simply be related to declaring only the information that is essential for methods (blocks of code) to function. This can also be defined as a system of hiding certain attributes and using syntax to contain or relay the essential functions.

Abstractions can be effectively used by employing both abstract classes and interfaces. This allows users to build functions without extensively declaring bodies during the implementation of methods.

It might not be feasible to define the abstract class and the interface systems without differentiating them. Once understanding both, you’ll be able to decide which to choose and how to use each. So, let’s determine the concepts and explain their differences.

 

https://www.google.com/imgres?interfaces-and-abstractclasses.webp

What Is an Interface?

Interfaces can be defined as blueprints of classes. Interfaces have abstract methods and static constants that work together to achieve true abstraction. Interfaces can only support abstract methods and variables in Java and not the method bodies. Interfaces are especially helpful when working with multiple interfaces.

Interface in Java can also help when trying to represent IS-A relationships that are based on inheritance. The inheritance here can also be divided into two subtypes, interface inheritances and class inheritances. On more modern compilers, we can use both static, private, and default methods when applying interfaces. Interfaces can also be used for achieving loose coupling.

Declaring interfaces is easy and can be done by simply using the ‘interface’ keyword. This allows the declaring of every method in the interface with empty bodies, thus providing complete abstraction. Classes that implement interfaces must be created so that every method declared is implemented.

Here is the syntax for implementing interfaces:

interface <example>{    
    // declaration of constant fields  
    // declaration of methods that abstract  
} 

What is an Abstract Class?

Abstract classes are classes that are declared in an abstract manner or that promote abstraction. However, unlike interfaces, abstract classes contain both non-abstract methods and abstract methods.

They need their methods to be implemented and the classes to be extended. These classes cannot be instantiated and must be declared with the ‘abstract’ keyword.

Abstract classes are restricted classes that cannot be utilized for creating objects and these classes must be inherited from other classes. So, the ‘abstract’ keyword is used for both methods and classes, functioning as non-access modifiers. Abstract classes can have both static methods and constructors as well.

Abstract classes can work with final methods that enforce subclasses into retaining the original body of the method. So, these classes do not have bodies and can inherit the bodies of the sub-classes through regular and abstract methods.

Example of an Abstract class that has an abstract method:

In this example, Bike is an abstract class that contains only one abstract method run. Its implementation is provided by the Honda class.

abstract class Bike{  
  abstract void run();  
}  
class Honda4 extends Bike{  
void run(){System.out.println("running safely");}  
public static void main(String args[]){  
 Bike obj = new Honda4();  
 obj.run();  
}  
}

 https://www.google.com/imgres?abstract-class-vs-interface.webp

Differences and Similarities

All methods that are mentioned in the interface are public and abstracts implicitly. Abstract classes can even contain non-abstract methods. They can both have the methods and variables, and neither one can be instantiated. All the variables declared within an interface are final, while an abstract class might contain non-final variables.

When should you use an abstract class?

• An abstract class is a great choice if you are bringing into account the inheritance concept because it provides the common base class implementation to the derived classes.
• An abstract class is also good if you want to declare non-public members. In an interface, all methods must be public.
• If you want to add new methods in the future, then it is great to go with the abstract class. Because if you add new methods to the interface, then all of the classes that are already implemented in the interface will have to be changed in order to implement these new methods.

When Should You Use an Interface?

• If you are creating functionality that will be useful across a wide range of objects, then you must use an interface. Abstract classes, at the end of the day, should be used for objects that are closely related. But the interfaces are best suited for providing common functionality to unrelated cases.
• Interfaces are a great choice if you think that the API won’t be changing for a while.
• Interfaces are also a great choice. If you want to have something similar to the multiple inheritances, then you can implement various interfaces.
• If we are going to design the small, concise bits of functionality, then you must use interfaces. But if you are designing the large functional units, then you must use an abstract class.

But, at the end of the day, it all comes down to what you require and what you are going to do about it. The same functionalities can be accomplished with both interface and abstract classes. With the coding standards, the interface would help you accomplish the abstraction and polymorphism which are among the main principles of coding or programming.

It also helps to keep your code loosely coupled instead of tightly coupled, which happens when the high-level modules depend on the low-level modules as well. Interfaces can also be used for the dependency injection that makes it easier to mock the derived classes when testing.

Frequently Asked Questions

1. When should we use the abstract class and interface in Java?

Abstract classes should be used when working with non-abstract methods and interfaces only to support abstract methods. Interfaces should be used when working with instances of multiple inheritances.

2. Can interfaces and abstract classes be used together?

Yes, these two can easily work together when integrated into the code or functions while building Java programs.

3. Are members of an interface private?

No, members of an interface are all public by default; however, one can use private members in abstract classes.

4. Can abstract classes have a constructor?

Yes, abstract classes can have both constructors and static methods.

Published by-

Batch 2-Group2

Sankalp Ghadge

Sanket Lahoti

Smit Lahane

Nikhil Suryawanshi

Eklavya Chaudhari