On Day 26, we focus on Interfaces, another core pillar of OOP in Java. An interface is like a contract that defines methods (without implementation). A class that implements an interface must provide the implementation for all its methods. Interfaces help achieve 100% abstraction and allow multiple inheritance in Java.
1. Defining and Implementing an Interface
interface Animal {
void sound(); // abstract method by default
void eat();
}
class Dog implements Animal {
@Override
public void sound() {
System.out.println("Dog barks");
}
@Override
public void eat() {
System.out.println("Dog eats bones");
}
}
class Cat implements Animal {
@Override
public void sound() {
System.out.println("Cat meows");
}
@Override
public void eat() {
System.out.println("Cat drinks milk");
}
}
public class Main {
public static void main(String[] args) {
Animal a1 = new Dog();
Animal a2 = new Cat();
a1.sound();
a1.eat();
a2.sound();
a2.eat();
}
}
Explanation: The Dog and Cat classes implement the Animal interface by providing their own definitions of sound() and eat().
2. Multiple Interfaces
interface Printable {
void print();
}
interface Scannable {
void scan();
}
class Printer implements Printable, Scannable {
@Override
public void print() {
System.out.println("Printing document...");
}
@Override
public void scan() {
System.out.println("Scanning document...");
}
}
public class Main {
public static void main(String[] args) {
Printer p = new Printer();
p.print();
p.scan();
}
}
Explanation: Unlike classes, Java allows implementing multiple interfaces. This is how Java overcomes the lack of multiple class inheritance.
3. Why Use Interfaces?
- Provide complete abstraction.
- Allow multiple inheritance in Java.
- Standardize method signatures across different classes.
- Make code more flexible and scalable.
Summary
Interfaces define a contract for classes to follow. Using the implements keyword, a class provides specific implementations. Interfaces allow polymorphism, code reusability, and multiple inheritance.
