Case Study On Sales Tax Problem

[Jayaraj Jaganathan]

I have completed reading HF OOAD.

I am much interested in applying OOAD to the below problem.
I have completed the solution for the below problem.
Source Code

the above link gives you the source code
I request some one in this fourm to review my design


PROBLEM TWO: SALES TAXES

Basic sales tax is applicable at a rate of 10% on all goods, except books,
food, and medical products that are exempt. Import duty is an additional
sales tax applicable on all imported goods at a rate of 5%, with no
exemptions.

When I purchase items I receive a receipt which lists the name of all the
items and their price (including tax), finishing with the total cost of the
items, and the total amounts of sales taxes paid. The rounding rules for
sales tax are that for a tax rate of n%, a shelf price of p contains
(np/100 rounded up to the nearest 0.05) amount of sales tax.

Write an application that prints out the receipt details for these shopping
baskets...

INPUT:

Input 3:
1 imported bottle of perfume at 27.99
1 bottle of perfume at 18.99
1 packet of headache pills at 9.75
1 box of imported chocolates at 11.25

OUTPUT


Output 3:
1 imported bottle of perfume: 32.19
1 bottle of perfume: 20.89
1 packet of headache pills: 9.75
1 imported box of chocolates: 11.85
Sales Taxes: 6.70
Total: 74.68

[David Newton]

SalesTax.java:

package org.thoughtworks.sales.stage.cart;

import java.math.BigDecimal;

import org.thoughtworks.sales.stage.dc.Item;
import org.thoughtworks.sales.stage.dc.ItemType;

public class SalesTax {

	/**
	 * Rounding factor.
	 */
	private static final BigDecimal ROUND_FACTOR = new BigDecimal("0.05");

	private static final BigDecimal domesticTaxPercentage = new BigDecimal("10");

	private static final BigDecimal additionalImportedTaxPercentage = new BigDecimal("5");

	private static BigDecimal taxPercentage = null;

	public void calculateTax(Item item) {
		calculateTaxPercentage(item);
		calculateSalesTax(item);
	}

	/**
	 * Calculate tax percentage for items<BR>
	 * Sales tax is applicable at a rate of 10% on all goods, except books,<BR>
	 * food, and medical products that are exempt. Import duty is an additional<BR>
	 * sales tax applicable on all imported goods at a rate of 5%, with no<BR>
	 * exemptions.
	 * 
	 * @param item
	 *            item for sales.
	 */
	private void calculateTaxPercentage(Item item) {

		ItemType type = item.getItemType();

		if (type.equals(ItemType.BOOK) || type.equals(ItemType.FOOD) || type.equals(ItemType.MEDICAL)) {
			taxPercentage = new BigDecimal("0.00");
		} else {
			taxPercentage = domesticTaxPercentage;
		}

		if (item.isImported()) {
			taxPercentage = taxPercentage.add(additionalImportedTaxPercentage);
		}
	}

	/**
	 * Calculate Sales Tax for an item.
	 * 
	 * @param item
	 *            item for sales.
	 */
	private void calculateSalesTax(Item item) {
		BigDecimal salesTax = item.getCost().multiply(taxPercentage).divide(new BigDecimal("100"));
		salesTax = roundOff(salesTax);
		item.setSalesTax(salesTax);
	}

	/**
	 * Returns the value rounded up to the nearest 0.05.
	 * 
	 * @param value
	 *            value to be rounded
	 * @return double rounded up value
	 */
	private BigDecimal roundOff(BigDecimal value) {	
		value = value.divide(ROUND_FACTOR);
		value = new BigDecimal(Math.ceil(value.doubleValue()));
		value= value.multiply(ROUND_FACTOR);
		return value;
	}
	
}

Lines 10-12: Redundant comment.

Lines 15, 17: Constants should be named with all capital letters, with words separated by underscores.

Lines 26-35: Misleading comment: you use numeric values in the comment that are not defined in the method itself: if the constants change and the comments don't you're misleading the code maintainer.

Line 19: There's no reason to have this be an instance variable. (See next.)

Entire class: As written there's no good reason to have this be anything but static methods. If it implemented an interface and there were different ways of calculating the tax I could see it being a class.

Line 64: Misleading comment; uses values not defined locally.

Lines 70-75: I'm not a big fan of redefining parameter values; it's potentially misleading and I believe it should be avoided.

Design: I'm not convinced that an Item should have a sales tax field. Items don't really have sales tax: purchases do (or "line items" do, which is a combination of an item, a quantity, etc.).

Item.java:

Getter/setter comments: don't bother; it's obvious.

[Istvan Kovacs]

I'm not good at patterns, but isn't this a case where we should have different classes for the taxes, as their behaviour/applicability differs? Then they could be applied separately. (Would that be the Visitor? Strategy?)

[Jayaraj Jaganathan]

Thanks for your patient in reviewing my code and giving valuable feed back.

Please look into my new Design as per your comment

David Newton wrote:SalesTax.java

I have renamed into Tax.java due to requirement changes
Requirement 1
to
Requirement 2

Lines 10-12: Redundant comment.

I have removed it

Lines 15, 17: Constants should be named with all capital letters, with words separated by underscores.

I have changed it

Lines 26-35: Misleading comment: you use numeric values in the comment that are not defined in the method itself: if the constants change and the comments don't you're misleading the code maintainer.

You are right and I have changed it

Line 19: There's no reason to have this be an instance variable. (See next.)

I have changed it

Entire class: As written there's no good reason to have this be anything but static methods. If it implemented an interface and there were different ways of calculating the tax I could see it being a class.

if i use interface as below

  public interface Tax{
public void calculateTax(Item item);
} 

and implemented class say SalesTax . for requirement 1 this holds good
but when requirement changes which need Passport to determine SalesTax.
Even though I program to interface still there is no use, because i am going to change both
Tax.java and implemented class SalesTax.java

  public interface Tax{
public void calculateTax(Item item);
public void calculateTax(Item item,Passport passport);
} 

Please give your valuable comments on this

Line 64: Misleading comment; uses values not defined locally.

I am not clear on this . Please brief

Lines 70-75: I'm not a big fan of redefining parameter values; it's potentially misleading and I believe it should be avoided.

Please let me know how do you think this can be solved.

Design: I'm not convinced that an Item should have a sales tax field. Items don't really have sales tax: purchases do (or "line items" do, which is a combination of an item, a quantity, etc.).

I too agree and created a class names OrderDetail.java for line item which has an Item and tax .
and Order.java for an Purchace

Item.java:

Getter/setter comments: don't bother; it's obvious.