[Java] Abstract class

Abstract class

- A class that is declared with abstract keyword, is known as abstract class

- It can have abstract and non-abstract methods

1. Abstraction in java

- Abstraction is a process of hiding the implementation details 

- It showing only functionality to the user

- Abstraction lets you focus on what the object does instead of how it does it

1) Ways to achieve Abstraction

- Abstract class

- Interface

2. Example

abstract class Shape{ abstract void draw(); } class Rectangle extends Shape{ void draw(){ System.out.println("Drawing rec"); } } class Circle extends Shape{ void draw(){ System.out.println("draw circle"); } } public class Test{ public static void main(String[]args){ Shape s = new Circle(); s.draw(); } }

3. Abstract class having constructor, data member, methods

abstract class Bike{ Bike(){ System.out.println("Bike is created"); } abstract void run(); void changeGear(){ System.out.println("gear changed"); } } class Honda extends Bike{ void run(){ System.out.println("running"); } } public class Test{ public static void main(String[]args){ Bike obj = new Honda(); obj.run(); obj.changeGear(); } }

- If there is any abstract method in a class, that class must be abstract

- If you are extending any abstract class that have abstract method, you must either provide the implementation of the method or make this class abstraction