问题描述
作为学校作业的一部分，我正在编写一个程序，该程序将帮助确定一包百吉饼的总价格，而我的getTotalPrice（）方法所产生的值将推出正确的值，但是对于某些情况其中有两个零添加到最终值。我尝试使用setScale（）方法将小数点四舍五入为两个空格，但被告知这不是理想的解决方案。我以前从未使用过BigDecimals，所以我相信我的代码中缺少某些东西，有什么建议吗？请让我知道是否需要更多信息，我不太确定要包含/排除的代码。
// test that fails
@ParameterizedTest
@ArgumentsSource(BagArgumentsProvider_getTotalPrice.class)
void getTotalPrice_assertEquals_DiffBagelAmounts(Bag bag,BigDecimal cost) {
assertEquals(cost,bag.getTotalPrice());
}
//some to the produced errors
expected 3.99 but was 3.9900
expected 1.99 but was 1.9950
/**
* A bag of any quantity of a single type of bagel.
*
* @author Ellen Spertus
*
*/
public class Bagel {
private final Type type;
private Category currentCategory;
// Visible for Testing
protected static final BigDecimal OLD_FASHIONED_PRICE = new BigDecimal("0.50");
protected static final BigDecimal GOURMET_PRICE = new BigDecimal("0.70");
protected static final BigDecimal DAY_OLD_PRICE = new BigDecimal("0.35");
enum Type {
PLAIN("plain",Category.OLD_FASHIONED),POPPY_SEED("poppy seed",SESAME_SEED("sesame seed",ONION(
"onion",EVERYTHING("everthing",ASIAGO("asiago",Category.GOURMET),BLUEBerry("blueBerry",CINNAMON_RAISIN(
"cinnamon raisin",SUN_DRIED_TOMATO(
"sun dried tomato",Category.GOURMET);
private final String name;
private final Category category;
private Type(String name,Category category) {
this.name = name;
this.category = category;
}// end constructor
@Override
public String toString() {
return name;
}// end toString
}// end enum
enum Category {
OLD_FASHIONED(OLD_FASHIONED_PRICE),GOURMET(GOURMET_PRICE),DAY_OLD(DAY_OLD_PRICE);
private final BigDecimal price;
private Category(BigDecimal price) {
this.price = price;
}// end constructor
public BigDecimal getPrice() {
return price;
}// end getPrice
}// end enum
/**
* Constructs a bagel of the given type.
*
* @param the type
*/
public Bagel(Type type) {
this.type = type;
this.currentCategory = type.category;
}// end constructor
/**
* Gets the type of the bagel.
*
* @return the type of bagel
*/
public Type getType() {
return type;
}// end getType
/**
* Gets the category of the bagel.
*
* @return the category
*/
public Category getCategory() {
return currentCategory;
}// end get Category
/**
* Marks down this bagel.
*/
public void markDown() {
currentCategory = Category.DAY_OLD;
}// end markDown
}// end class
/**
* A type of bagel.
*
* @author Ellen Spertus
*/
public class Bag {
// We provide a Baker's Dozen: 13 bagels for the price of 12.
private static final int BUY_ONE_GET_ONE_FREE_QUANTITY = 13;
// If the Baker's Dozen discount doesn't apply,we give a percentage discount.
private static final int BULK_disCOUNT_MINIMUM = 6;
private static final BigDecimal BULK_disCOUNT_PERCENTAGE = new BigDecimal(".05");
private static final BigDecimal BULK_disCOUNT_MULTIPLIER =
new BigDecimal("1.00").subtract(BULK_disCOUNT_PERCENTAGE);
private final Bagel bagel;
private final int quantity;
/**
* Constructs a bag with the given quantity of the given type of bagel.
*
* @param bagel the type of bagel
* @param quantity the quantity
* @throws IllegalArguementException if the quantity passed is out of range from 1 to 13
*/
public Bag(Bagel bagel,int quantity) {
this.bagel = bagel;
this.quantity = quantity;
if (this.quantity > 13) {
throw new IllegalArgumentException("Orders must be under 13 bagels");
}
if (this.quantity < 1) {
throw new IllegalArgumentException("Not a valid order");
}
}// end constructor
/**
* Gets the bagel held in this bag.
*
* @return the bagel
*/
public Bagel getBagel() {
return bagel;
}// end getBagel
/**
* Gets the number of bagels in this bag.
*
* @return the number of bagels in this bag
*/
public int getQuantity() {
return quantity;
}// end getQuantity
/**
* Gets the total price for this bag of bagels. This may be less than the per-bagel price times
* the number of bagels because of quantity discounts.
*
* @return the total price
*/
public BigDecimal getTotalPrice() {
BigDecimal undiscountedPrice = getPerBagelPrice().multiply(new BigDecimal(quantity));
if (quantity == BUY_ONE_GET_ONE_FREE_QUANTITY) {
undiscountedPrice = undiscountedPrice.subtract(getPerBagelPrice());
}
if (quantity >= BULK_disCOUNT_MINIMUM) {
undiscountedPrice = undiscountedPrice.multiply(BULK_disCOUNT_MULTIPLIER);
}
//undiscountedPrice = undiscountedPrice.setScale(2,RoundingMode.HALF_UP);
return undiscountedPrice;
}// end getTotalPrice
/**
* Returns the price associated with the bagel type.
*
* @return price based on bagel type
*/
public BigDecimal getPerBagelPrice() {
return bagel.getCategory().getPrice();
}// end getPerBagelPrice
}
解决方法
哦！我相信我已经找到问题了！ .multiply（）方法将小数精度从2增加到4。解决方案是只创建一个精度为3的新MathContext，然后使用RoundingMode.Half_DOWN推出正确的价格值。
让我知道是否有更好的解决方案。
public BigDecimal getTotalPrice() {
System.out.println(getPerBagelPrice());
BigDecimal undiscountedPrice = getPerBagelPrice().multiply(new BigDecimal(quantity));
if (quantity == BUY_ONE_GET_ONE_FREE_QUANTITY) {
undiscountedPrice = undiscountedPrice.subtract(getPerBagelPrice());
}
if (quantity >= BULK_DISCOUNT_MINIMUM && quantity != 13) {
undiscountedPrice = undiscountedPrice.multiply(BULK_DISCOUNT_MULTIPLIER,new MathContext(3,RoundingMode.HALF_DOWN));
}
System.out.println(undiscountedPrice);
return undiscountedPrice;
}