Interfaces and Abstract Classes

Abstract

Definitions

Data Abstraction is the proccess of hiding certain details and showing only essential information to the user.
Abstraction can be achieved with either abstract classes or interfaces.

Java Abstract Classes and Methods

Abstract class: cannot be used to create objects, it must be inherited and implemented in a subclass.

Abstract method: can only be defined in an Abstract class and does not have a body. The body is implemented in a subclass.

An Abstract Class can have both abstract and regular methods.

// Abstract class
abstract class Animal {
  // Abstract method (does not have a body)
  public abstract void animalSound();
  // Regular method
  public void sleep() {
    System.out.println("Zzz");
  }
}

// Subclass (inherit from Animal)
class Pig extends Animal {
  public void animalSound() {
    // The body of animalSound() is provided here
    System.out.println("The pig says: wee wee");
  }
}

class MyMainClass {
  public static void main(String[] args) {
    Pig myPig = new Pig(); // Create a Pig object
    myPig.animalSound();
    myPig.sleep();
  }
}

Interface

Another wy of achieve abstraction in Java, is with interfaces.

An Interface is a pure abstract class.