Understanding Interfaces in Java: A Beginner’s Guide

 

In Java, interfaces are a crucial part of object-oriented programming (OOP). They provide a way to achieve abstraction and multiple inheritance. If you are new to Java, understanding interfaces can open up new possibilities for designing flexible, scalable applications. In this blog, we will explore what an interface is, why it's useful, and how to implement it effectively in Java.

 

What is an Interface in Java?

•  An interface in Java is a blueprint of a class. It has static constants and abstract methods.
• The interface in Java is a mechanism to achieve abstraction. There can be only abstract methods in the Java interface, not method body. It is used to achieve abstraction and multiple inheritance in Java.
• In other words, you can say that interfaces can have abstract methods and variables. It cannot have a method body.
• With Java 8, interfaces gained the ability to have default methods and static methods in an interface.
• With Java 9, interfaces gained the ability to have private methods in an interface.

Syntax:

interface < interface_name > {

    // declare constant fields  

    // declare methods that abstract   

    // by default.  

}  

Here’s a simple example of an interface:

public interface Student {

    void accept();  // Abstract method

    void display();  // Abstract method

  }

Why we use Interfaces?

• Interfaces are used for a variety of reasons:
• It is used to achieve total abstraction.
• Since java does not support multiple inheritances in the case of class, by using an interface it can achieve multiple inheritances.
• Any class can extend only one class, but can implement multiple interfaces.
• It is also used to achieve loose coupling.
• Interfaces are used to implement abstraction. 

 

Implementing an Interface

When a class implements an interface, it provides concrete implementations for all the abstract methods defined in the interface. Let’s implement the Animal interface from the previous example:

public class Dog implements Animal {

    @Override

    public void accept() {

        System.out.println("Student name is Ram.");

    }

    @Override

    public void display() {

        System.out.println("Displaying name of Student: Ram.");

    }

 

Interfaces and Multiple Inheritance

As mentioned earlier, a class can implement multiple interfaces, which allows Java to circumvent the restriction of multiple inheritance with classes. Here’s an example:

public interface Walker {

    void walk();

}

public class Name implements Student,School {

    @Override

    public void accept() {

        System.out.println("Student name is Ram.");

    }

    @Override

    public void display() {

        System.out.println("Displaying name of Student: Ram.");

    }

    @Override

    public void school_name() {

        System.out.println("Cambridge.");

    }

}

Conclusion

Interfaces are a powerful tool in Java that promote flexibility, abstraction, and code reusability. Whether you are building a simple application or a complex system, understanding and leveraging interfaces will help you design better software.