CalculateElectricityBill.java

package Solutions;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;


//Calculate Electricity Bill : A Real World Example of Factory Method
abstract class Plan {

	protected double rate;

	abstract void getRate();

	public void calculateBill(int units) {
		System.out.println(units * rate);
	}
}

class DomesticPlan extends Plan {
	// @override
	public void getRate() {
		rate = 3.50;
	}
}

class CommercialPlan extends Plan {
	// @override
	public void getRate() {
		rate = 7.50;
	}
}

class InstitutionalPlan extends Plan {
	// @override
	public void getRate() {
		rate = 5.50;
	}
}

class GetPlanFactory {
	public Plan getPlan(String planType) {
		if (planType == null) {
			return null;
		}
		if (planType.equalsIgnoreCase("DOMESTICPLAN")) {
			return new DomesticPlan();
		} else if (planType.equalsIgnoreCase("COMMERCIALPLAN")) {
			return new CommercialPlan();
		} else if (planType.equalsIgnoreCase("INSTITUTIONALPLAN")) {
			return new InstitutionalPlan();
		}
		return null;
	}
}

public class CalculateElectricityBill {

	public static void main(String args[]) throws IOException {
		GetPlanFactory planFactory = new GetPlanFactory();

		System.out.print("Enter the name of plan for which the bill will be generated: ");
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		String planName = br.readLine();
		System.out.print("Enter the number of units for bill will be calculated: ");
		int units = Integer.parseInt(br.readLine());

		Plan p = planFactory.getPlan(planName);
		// call getRate() method and calculateBill()method of DomesticPaln.
		System.out.print("Bill amount for " + planName + " of  " + units + " units is: ");
		p.getRate();
		p.calculateBill(units);
	}

}