Inheritance

Consider a shop where there are two types of customers Regular and Privileged customer

what is the difference between them:

Regular Customer:- These type of customer get discount of some percentage on the products

Privileged Customer:-These type of customers get gift on their membership card

How this could be implemented?

by Inheritance

Here Customer class is generalized once and Regular and Privileged Customers

• Inheritance is a mechanism inn which class A inherit all the properties of class B and said "class A inherit class B"
• All the methods and variables are available to class A
• A class which is inherited (here class B) is called Super class,Base class or Parent class
• A class which is inherits from another class (here class A) is called Derived class or Child class 
• In Java, keyword used is "extends"
• Inheritance promotes reuse. if type of customer id to be added then we can use the Customer details form Customer class

Types of Inheritance

• Single inheritance

                                             

• Multi-Level Inheritance

                                                     

• Multiple Inheritance

                              
Multiple Level Inheritance is not allowed in java classes but they are implemented in Interfaces

Thinks of the scenario Retails store case study where customers are of two type Regular and Privileged customers what are the attributes of 
Regular customer
Attribute : discount
Privileged customer
Attribute : membership card
Both the type of customer have different attributes now what are similar attributes
Attributes : customer name
                     customer id
                     customer address
Lets draw a class diagram and understand the concept 

Here customer class have all the common fields and methods and both other types inherit all the properties from customer class and also have their own specific methods

class Customer{

       private int customerId;

       public void setCustomerId(int customerId){

  this.customerId=customerId;

        }

        public int getCustomerId(){

  return customerId;

        }

}

class RegularCustomer extends Customer{

       private float discount;

       public void setDiscount(float discount){

  this.discount=discount;

       }

  

       public float getDiscount(){

  return discount;

       }

}

class PrivilegedCustomer extends Customer{

       private String memCardType;

       public void setMemCardType(String cardType){

  this.memCardType=cardType;

       }

       public String getMemCardType(){

  return memCardType;

       }

}

class Retail{

public static void main(String args[]){

  RegularCustomer regObj=new RegularCustomer();

  PrivilegedCustomer prvObj = new PrivilegedCustomer();

  regObj.setCustomerId(1001);

  regObj.setDiscount(20.00f);

  prvObj.setCustomerId(2001);

  prvObj.setMemCardType("Gold");

  System.out.println("Regular Customer Details");

  System.out.println("Customer Id:" +regObj.getCustomerId());

  System.out.println("Discount:"+regObj.getDiscount());

  System.out.println("Privileged Customer Details");

  System.out.println("Customer Id:"+prvObj.getCustomerId());

  System.out.println("Membership Card Type:"+prvObj.getMemCardType());

}

}

Output:

Regular Customer Details

Customer Id: 1001

Discount: 20.0

Privileged  Customer Details

Customer Id: 2001

Membership Card Type: Gold

What is the Output?

class Base{

  public Base(){

  System.out.println("Base class constructor");

  }

}

class Der extends Base{

  public Der(){

  System.out.println("Derived class constructor");

  }

}

class Demo{

  public static void main(String args[]){

  Der Derobj=new Der();

  }

}