Factory Design Pattern In Java

            /* ............... START ............... */
                //Calculate Electricity bill a real world Example.

// Step1 

//We are going to create a Plan abstract class. 
/*we are using io concept in our class that's why we are importing io pacakage.*/
import java.io.*; 

abstract class Plan

{
	protected double rate;

	abstract void getRate();

	public void calculateBill(int units)

	{

		System.out.println(units * rate);
	}

}

// Step 2 

// We are going to create a Concrete classes that extends Plan abstract class.

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;
	}
}

// Step 3 

// Create a GetPlanFactory to generate object of concrete classes based on given
// information.

class GetPlanFactory {

	// use getPlan method to get object of type Plan

	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;
	}
}

// Step 4

// Use the GetPlanFactory to get the object of concrete classes by passing an
// information such as type(DOMESTICPLAN/COMMERCIALPLAN/INSTITUTIONALPLAN).

class GenerateBill {

	public static void main(String args[]) throws IOException {

		GetPlanFactory planFactory = new GetPlanFactory();

		// get an object of DomesticPaln and call its getPlan()method.But we want to
		// calculate the bill for one plan at time not all.for this we IO concept.

		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);

	}
}// end of GenerateBill class.

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