Java Abstraction

Data Abstraction in Java is the process of hiding certain details and showing only essential information to the user.

Java Abstract Classes and Methods

Abstraction in Java can be achieved using the abstract classes and interfaces. The abstract keyword is a non-access modifier, used for classes and methods:

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

Note: The abstract class can have both abstract method and normal method.

Example:

abstract class AnimalSound {
       public void sleep(){
              System.out.println("Zzzzz");
       }
       public abstract void animalSound();
}

From the above example, it is not possible to create object for the class AnimalSound . The below code throws an error:

AnimalSound myAnimal = new AnimalSound();

The following error has been generated:

Exception in thread "main" java.lang.Error: Unresolved compilation problem:
       Cannot instantiate the type AnimalSound
 
       at practices.AnimalSoundClass.main(AnimalSoundClass.java:5)

To access the Abstract class, it should be inherited to its sub class. We use extend keyword to inherit from the Abstract class as well.

Example

AnimalSound.java

abstract class AnimalSound {
       public void sleep(){
              System.out.println("Zzzzz");
       }
       public abstract void animalSound();
}
 
class Dog extends AnimalSound{
       public void animalSound(){
              System.out.println("Dog makes bow bow sound");
       }
}
 
class Cat extends AnimalSound{
       public void animalSound(){
              System.out.println("Cat makes meow meow sound");
       }
}
 
class Cow extends AnimalSound{
       public void animalSound(){
              System.out.println("Cow makes moo moo sound");
       }
}

AnimalSoundClass.java

public class AnimalSoundClass {
       public static void main(String args[]){
              AnimalSound myDog = new Dog();
              AnimalSound myCat = new Cat();
              AnimalSound myCow = new Cow();
             
              myDog.animalSound();
              myCat.animalSound();
              myCow.animalSound();
              myDog.sleep(); //Accessing the abstract class "Regular method"
       }
}

Output

Dog makes bow bow sound
Cat makes meow meow sound
Cow makes moo moo sound
Zzzzz

Why use Abstract class and methods?

Through Abstract class and methods, we achieve security of the code and show only the important details of an object. Data Abstraction can also be achieved through Interfaces.