Module 31: Interfaces in Java

🔌 What is an Interface?

An interface in Java is a reference type, similar to a class, that can contain only constants, method signatures, default methods, static methods, and nested types. Interfaces cannot contain instance fields or constructors.

📌 Key Features

• Methods in interfaces are abstract by default (till Java 7).
• From Java 8 onwards, interfaces can have default and static methods.
• Used to achieve 100% abstraction.
• Supports multiple inheritance in Java through interfaces.

🧪 Example: Interface Implementation

                    interface Animal {
                      void sound();
                    }
                    
                    class Dog implements Animal {
                      public void sound() {
                        System.out.println("Dog barks");
                      }
                    }
                    
                    public class Main {
                      public static void main(String[] args) {
                        Animal a = new Dog();
                        a.sound();  // Output: Dog barks
                      }
                    }

🧠 Interface vs Abstract Class

• Abstract class can have both abstract and concrete methods; interface methods are abstract (until Java 7).
• Multiple inheritance is possible using interfaces but not with abstract classes.
• Interfaces cannot have constructors or instance variables.