Java Abstraction

What does abstract java class means?

1. It is one of the fundamental feature of Object Oriented Programming  language
2. It is super class and cannot be instantiated
3. It is used to state and define general characteristic
4. An object cannot be created using abstract class if trying to instantiated; it produces compile time error
5. The abstract class declares using “abstract” java keyword
6. An abstract class may be abstract method, member variables and concrete methods
7. It helps reduce the complexity and also improve the maintainability of the system

Abstract java class Characteristic: 

You cannot create the abstract java class instance. Let see in example mentioned below

public abstract class AbsExample { 

public String name;

     

public void display(String name){

      this.name = name;      

}    

public static void main(String[] args) {

    AbsExample abs = new AbsExample(); // Cannot instantiate the type AbsExample

      }

}

We can access the abstract class using its sub class only and we can create n number of subclass for single abstract class. Once subclasses extend to any parent java class then it cannot be extend by any other parent java class.

public abstract class AbsExample{  

      public String name;

     

      public void display(String name){

            this.name = name;

            System.out.println(this.name);     

      }    

}

Create a subclass which extend to parent java class

public class SubChildAbs extends AbsExample{

      public static void main(String[] args) {

            AbsExample absExample = new SubChildAbs();

            absExample.display("Hello Abstract Class");

      }

}

Output: “Hello Abstract Class”

An abstract method is a method that can declare in abstract class without implementation as method in below example

abstract int calculation(int a,int b);

If any class includes abstract method, then class itself declared as Abstract class. Otherwise it will give you below compile time error

public class HelloWorld {

//The type HelloWorld must be an abstract class to define abstract methods

      void display(){

            System.out.println("Display Hello World");           

      }

     

//The abstract method helloworldMessage in type HelloWorld can only be defined by an abstract class

      abstract void helloworldMessage();

}

Abstraction Examples:

 

In simply word, I can say that abstraction is used to hiding the implementation or system details behind the simple interface.

Let’s take an example of CAR

We can see the color, modal, look, seating capacity, space, gear but you cannot see the internal mechanism of car like how engine work?

Another example: Serializable interface

As we know that serializable interface as known as marker interface and which has no method defined in it but when we implement serializable interface so it serialized the object. So here seriablable interface is abstract layer for us but internally JVM serialize the object. (Hiding the implementation or system details behind the simple interface.)

Advantage of abstract class:

1. We can separate the things and grouped to another type
2. It Simplifies the representation of domain modal
3. We can separate in group the things which frequently changes their properties and methods so main group type need not undergo changes 

Summary:

It is one of the main features of OOPs fundamental which helps to reduce the complexity and also improve the maintainability of the system. It used to state and define general characteristic.