[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

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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

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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