Understand Difference

Mastering Classes and Interfaces: Building Blocks for Clean and Reusable Code

Introduction to Class and

Interface in Object-Oriented Programming

The world of software development is rapidly expanding, and it is necessary for programmers to stay up-to-date with new technologies and programming languages. One of the most important programming paradigms is

Object-Oriented Programming (OOP), which enables developers to create modular and reusable code.

The backbone of OOP is classes and interfaces, which serve as blueprints for creating objects. In this article, we will provide an overview of the fundamental concepts of classes and interfaces, their properties and methods, syntax, and access modifiers.

By the end of the article, you will have a sound understanding of these concepts and be well-equipped to incorporate them into your programs.

Object-Oriented Programming (OOP)

Before diving into the specifics of classes and interfaces, it’s essential to understand the basics of OOP. OOP is a programming paradigm that models real-world objects into software components.

The goal of OOP is to create modular, reusable code that is easy to maintain, modify, and expand. In OOP, everything is considered an object, which has properties and methods.

Properties are the characteristics that define an object, and methods are the actions that an object can perform. One of the significant advantages of OOP is its ability to minimize code repetition, thereby promoting code reuse.

In traditional programming, every piece of functionality requires new code. With OOP, you can create a common blueprint for an object that you can reuse throughout your program.

This blueprint is what we call a class.

Definition of Class and


A class is an essential building block of OOP. It is a template or blueprint that defines the properties and methods that an object can have.

Think of a class as a set of instructions that are used to create an object. An interface is similar to a class but with the essential distinction that it only defines the methods but not the implementation of those methods.

Interfaces are like contracts that tell classes how to behave. In other words, an interface says what an object should be able to do, but it doesn’t say how to do it.

Properties and Methods of a Class

A class comprises properties and methods. Properties define the characteristics of an object, while methods define the actions that an object can perform.

For instance, let’s consider a car object. Its properties could include the make, model, and year of the vehicle, while its methods may include accelerating, braking, or changing gears.

When creating a class, consider the properties that will provide the necessary information about the object and the methods that will provide the functionality needed to interact with the object. It is important to choose descriptive names for your properties and methods to make it easier to understand your code.

Syntax of Class and Object Creation

The syntax of a class follows a specific structure. A class declaration begins with the keyword “class,” followed by the class name and a pair of braces that contain the class’s variable declarations and method definitions.

For example, here is the syntax of a simple car class:

class Car {

// Properties

private String make;

private String model;

private int year;



public Car(String make, String model, int year) {

this.make = make;

this.model = model;

this.year = year;


// Methods

public void accelerate() {

// Code to increase the car’s speed


public void brake() {

// Code to decrease the car’s speed



As you can see, we need to create a constructor method that initializes the properties of the class. In the example, the constructor initializes the make, model, and year properties with the values provided as parameters.

To create an object of the Car class, we use the “new” keyword, followed by the name of the class and any required parameters.

Access Modifiers of Class Members

Access modifiers, also known as access specifiers, are used to control the class’s visibility and accessibility. In Java, there are three access modifiers: public, private, and protected.

Public access modifier makes the member accessible to all classes and objects, while the private access modifier makes the member visible only within the class. The protected access modifier provides visibility to the member within the same package and its subclasses.

In the example of the Car class, we used the private modifier to limit access to the make, model, and year properties. We also used the public modifier to allow access to the accelerate() and brake() methods.


In conclusion, classes and interfaces are crucial components of OOP, and their proper utilization can help you create clean, modular, and maintainable code. When creating classes, remember to define the properties and methods carefully and choose appropriate access modifiers to ensure your code’s integrity.

Interfaces are powerful tools that allow you to define contracts that classes must adhere to, ensuring interoperability between objects. By implementing these concepts, you can improve the overall quality of your code, making it more scalable, maintainable, and efficient.


In Object-Oriented Programming, the interface refers to an abstract type that establishes a contract between the class and the outside world. An interface defines a group of methods that an implementing class should implement.

It provides a way of separating the implementation details of different classes from each other and improves code security.

Abstraction in Object-Oriented Programming

The key concept behind interfaces is abstraction, which is the process of focusing on essential features while ignoring non-essential details. An abstract class is similar to an interface, except it can have some implementation details that concrete classes can inherit.

On the other hand, an interface has no implementation details and hence, all methods are declared abstract. Using interfaces, you can create a set of functionality that can be implemented by different classes in different ways.

By eliminating the implementation details from the interface, you can focus on the user’s perspective on the system. This way, the implementation can be changed without affecting other parts of the system.

Creation and Syntax of


Like a class, an interface provides a set of methods. However, the interface only declares the methods that should be implemented.

The syntax of an interface, therefore, consists of method declarations and no implementation code. Here is an example interface:

public interface Shape {

public double getArea();

public double getPerimeter();


The above interface defines two methods, a getArea() and a getPerimeter().

These methods should be implemented by any class that implements Shape. After creating an interface, you can create an object of any class that implements it.

This is because the object implementation is hidden inside the implementing class, making it invisible to the outside world. Implementation of

Interface by Classes

In Java, a class can inherit from only one superclass.

However, a class can implement multiple interfaces. This is because an interface declares a contract that a class promises to implement, while a superclass defines everything a class is.

Implementing an interface involves making a concrete implementation of the abstract methods declared in the interface. The implementation must follow the syntax of the interface.

Here is an example of a class that implements the Shape interface:

public class Circle implements Shape {

private double radius;

public Circle(double radius) {

this.radius = radius;


public double getArea() {

return radius * radius * Math.PI;


public double getPerimeter() {

return radius * 2 * Math.PI;



In the above example, the Circle class implements the Shape interface. It provides an implementation for both the getArea() and getPerimeter() methods defined in the Shape interface.

Public Members of


All the members of an interface are, by default, public. This means that all the implementing classes get access to the public members of the interface for implementation.

Here is an example of an interface that declares a public method:

public interface Draw {

public void drawShape();


The above interface declares a public method called drawShape(). This method can be accessed by any implementing class.

Similarities Between Class and


Both class and interface are reference types used in Object-Oriented programming. Reference types are those that hold the memory address of the object they refer to.

When creating an instance of a class or interface, you are creating an object that uses the memory allocated by the system. Both class and interface are related to Object-Oriented programming.

In Object-Oriented programming, classes are used as building blocks for creating objects. An interface defines a contract that the implementing class should fulfill.


In conclusion, interfaces are a powerful tool in Object-Oriented programming that allows you to create code with a high degree of flexibility. The use of interfaces can help you create code that can be easily modified and maintained, making it a valuable asset in software development.

By understanding the syntax and implementation details of interfaces, you can improve your coding skills and prepare yourself for working with complex software projects. Difference Between Class and


In Object-Oriented Programming, classes and interfaces serve different purposes when creating software.

While both are key building blocks for creating objects, they differ in syntax, functionality, keyword usage, and object instantiation. By understanding the differences between classes and interfaces, you can make more informed decisions when designing and implementing software systems.

Object Instantiation

One of the key differences between classes and interfaces is how they are used to create objects. To create an object from a class, you instantiate it using the new keyword and assign it to a variable.

This creates an instance of the class, which has access to all the class’s fields and methods. On the other hand, you cannot create an instance of an interface.

Instead, you define the interface, which sets the contract for how objects should behave. Then, you create one or more classes that implement the interface, and you create instances of the implementing classes instead of the interface itself.


Constructors are another area where classes and interfaces differ. A constructor is a special method that is called when an object is created.

It is used for initializing the object’s fields and preparing it for use. In a class, the constructor is defined using the name of the class and is used to create and initialize objects of that class.

For example, here is a simple class with a constructor:

public class Person {

private String name;

public Person (String name) {

this.name = name;



In contrast, an interface cannot have a constructor because it has no implementation. An interface only specifies a set of methods that a class must implement.

Any implementation details must be included in the implementing class.


The keyword used to define classes and interfaces is also another significant difference between them. A class is designated using the keyword “class,” while an interface is designated using the keyword “interface.” This keyword difference reflects the primary differences between classes and interfaces; classes define objects, while interfaces establish a contract between objects.

For example, here is the syntax to define a class named Person:

public class Person {

// Class Fields and Methods


And, here is the syntax to define an interface named IAttack:

public interface IAttack {


Interface Methods


Access Specifier

Access specifiers define how members of a class or interface should be accessed by other parts of the software. Classes and interfaces differ in how they apply access specifiers to their members.

In classes, access specifiers can be used to limit the visibility of fields and methods. For example, a private access specifier can be used to limit access to a field to only that class.

A public access modifier, on the other hand, gives unrestricted access to the field or method. In interfaces, however, all interface members are public by default.

This is because an interface can only define a set of abstract methods that must be implemented by any class that implements the interface. Since these methods are designed to be implemented and used by other classes, they are typically marked as public for broad accessibility.


To summarize, classes and interfaces are two essential building blocks of Object-Oriented Programming. While both have some similarities in the sense that they define objects, they differ in their syntax, functionality, keyword usage, object instantiation mechanisms, and access specifier usage.

Classes create objects and can have constructors, while interfaces only define a set of methods that must be implemented by a class. The interface is an abstract entity that defines the behavior of implementing objects, while a class is an actual object that has implementation details.

By understanding the differences between them, you can create more robust and scalable software systems. In conclusion, understanding the concepts of classes and interfaces is crucial in Object-Oriented Programming.

Classes serve as blueprints for creating objects with properties and methods, allowing for code reuse and modularity.

Interfaces, on the other hand, establish contracts for implementing classes, promoting abstraction and code security.

By recognizing the differences between classes and interfaces, you can design more flexible and maintainable software systems. Remember to consider object instantiation, constructors, keywords, and access specifiers when working with classes and interfaces.

These concepts empower you to create clean and scalable code, improving the efficiency and quality of your programs. Embrace the power of classes and interfaces in your programming journey, and unlock a world of possibilities in software development.

Popular Posts