Java Abstraction

Java Abstraction

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

The abstract keyword is a non-access modifier, used for classes and methods:

• Abstract class: A restricted class that cannot be used to create objects (to access it, it must be inherited from another class).
• Abstract method: Can only be used in an abstract class, and it does not have a body. The body is provided by the subclass (inherited from).

Why Use Abstract Classes and Methods?

Abstraction allows you to define a "contract" or a template for a group of subclasses. It lets you define some common behavior in the abstract class itself, while forcing subclasses to provide their own implementation for the abstract methods.

This helps to achieve security - hide certain details and only show the important details of an object.

Abstract Class Example

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 {
  // The body of animalSound() is provided here
  public void animalSound() {
    System.out.println("The pig says: wee wee");
  }
}
class Main {
  public static void main(String[] args) {
    // Animal myObj = new Animal(); // will generate an error
    Pig myPig = new Pig(); // Create a Pig object
    myPig.animalSound();
    myPig.sleep();
  }
}

In this example:

• You cannot create an object of the Animal class.
• The Pig class must implement the animalSound() method, otherwise it would also need to be declared as abstract.
• The Pig object can use both the implemented animalSound() method and the inherited sleep() method.