Java – Factory Design Pattern – Ameerpet Technologies

Factory Design Pattern: Define interface or abstract class for creating an object but let the subclasses decide which class to instantiate.

import java.util.*;
abstract class Plan
{
            abstract double getRate();
            public void calculateBill(double rate, int units)
            {
                        System.out.println(units*rate);
            }
}
class DomesticPlan extends Plan
{
            public double getRate()
            {
                        return 3.50;
            }
}
class CommercialPlan extends Plan
{
            public double getRate()
            {
                        return 7.50;
            }
}
class InstitutionalPlan extends Plan
{
            public double getRate()
            {
                        return 5.50;
            }
}

class GetPlan
{
            public Plan getPlan(String plan)
            {
                        if(plan == null)
                        {
                                    return null;
                        }
                        if(plan.equals(“domestic”))
                        {
                                    return new DomesticPlan();
                        }
                        else if(plan.equals(“commercial”))
                        {
                                    return new CommercialPlan();
                        }
                        else if(plan.equals(“institutional”))
                        {
                                    return new InstitutionalPlan();
                        }
                        return null;
            }
}
class GenerateBill
{
            public static void main(String args[])
            {
                        GetPlan plan = new GetPlan();
                        System.out.print(“Enter plan name : “);

                        Scanner sc = new Scanner(System.in);
                        String name = sc.next();

                        System.out.print(“Enter units : “);
                        int units = sc.nextInt();

                        Plan p = plan.getPlan(name);
                        System.out.print(“Bill for ” + name + ” plan of ” + units + ” units is : “);
                        double rate = p.getRate();
                        p.calculateBill(rate, units);
            }
}

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