Java Class vs Interfaces

In Java, classes and interfaces are fundamental components used to design and organize programs. A class represents objects by defining their data and operations, whereas an interface specifies a contract for implementing common behavior. Choosing between them depends on how the functionality needs to be defined and shared.

• Classes support object creation, constructors, and state management.
• Interfaces promote abstraction and allow a class to implement multiple behavioral contracts.

A class can extend another class and implement an interface, while an interface can only extend another interface, not implement a class.

Class

A class is a blueprint for creating objects. It encapsulates fields (state) and methods (behavior) that are common to all objects of that type.

class Student{
    
    //data member (also instance variable) 
    int id; 
    
    //data member (also instance variable)  
    String name;

    public static void main(String args[]){
        
        //creating an object of Student
        Student s1=new Student();  
        System.out.println(s1.id);  
        System.out.println(s1.name);  
    }  
}

0
null

Explanation: Above code defines a Student class with two instance variables, id and name, and creates an object to demonstrate default values. It shows that objects of a class can hold state and access its fields.

Interface

An interface in Java defines a contract that classes can implement to provide specific behavior. Interface variables are implicitly public, static, and final, while abstract methods are implicitly public and abstract. Since Java 8, interfaces can also contain default and static methods, and since Java 9, they can contain private methods.

import java.io.*;

// Interface Declared
interface testInterface{
  
    // public, static and final
    final int a = 10;

    // public and abstract
    void display();
}

// Class implementing interface
class TestClass implements testInterface{
  
    // Implementing the capabilities of Interface
    public void display(){ 
      System.out.println("Geek"); 
    }
}

class Geeks{
    
    public static void main(String[] args){
        
        TestClass t = new TestClass();
        t.display();
        System.out.println(t.a);
    }
}

Geek
10

Explanation: Above code defines an interface with a constant and an abstract method, then implements it in a class providing method behavior. It demonstrates how a class can adopt an interface and use its constants and methods.

Class vs Interface

The following table lists all the major differences between an interface and a class in Java.