java abstraction class | abstraction in java with realtime example

Java abstract Keyword

The abstract keyword is used to achieve abstraction in Java. It is a non-access modifier which is used to create abstract class and method.

The role of an abstract class is to contain abstract methods. However, it may also contain non-abstract methods. The method which is declared with abstract keyword and doesn't have any implementation is known as an abstract method.

Abstract class in java

Syntax:-  

     abstract class Employee  

{  

     abstract void work();  

}   

Rules of abstract keyword

Don'ts

• An abstract keyword cannot be used with variables and constructors.
• If a class is abstract, it cannot be instantiated.
• If a method is abstract, it doesn't contain the body.

• We cannot use the abstract keyword with the final.

• We cannot declare abstract methods as private.

• We cannot declare abstract methods as static.

• An abstract method can't be synchronized.

Do's

• An abstract keyword can only be used with class and method.
• An abstract class can contain constructors and static methods.
• If a class extends the abstract class, it must also implement at least one of the abstract method.
• An abstract class can contain the main method and the final method.
• An abstract class can contain overloaded abstract methods.
• We can declare the local inner class as abstract.
• We can declare the abstract method with a throw clause

Examples of abstract Keyword

    abstract class Vehicle  

{  

    abstract void bike();  

      

}  

     class Honda extends Vehicle  

{  

  

    @Override  

    void bike() {  

        System.out.println("Bike is running");  

      

    }  

      

}  

  

    public class AbstractExample1 {  

  

      public static void main(String[] args) {  

  

    Honda obj=new Honda();  

    obj.bike();  

    }         

} 

Output:

Bike is running