要为酿酒厂构建的订单处理系统有三个主要对象：一个 PricingEngine 处理包含折扣的业务规则，一个 WholeSaleOrder 代表订单，一个 Money 类型代表钱。
第一个要编写的类是 Money 类，它有进行加、乘和减的方法。可以用 JUnit 测试新创建的类，如清单 14 所示：
清单 4. JUnit 的 MoneyTest 类
package org.acme.store;
import junit.framework.TestCase;
public class MoneyTest extends TestCase {
public void testToString() throws Exception{
Money money = new Money(10.00);
Money total = money.mpy(10);
assertEquals("$100.00", total.toString());
}
public void testEquals() throws Exception{
Money money = Money.parse("$10.00");
Money control = new Money(10.00);
assertEquals(control, money);
}
public void testMultiply() throws Exception{
Money money = new Money(10.00);
Money total = money.mpy(10);
Money discountAmount = total.mpy(0.05);
assertEquals("$5.00", discountAmount.toString());
}
public void testSubtract() throws Exception{
Money money = new Money(10.00);
Money total = money.mpy(10);
Money discountAmount = total.mpy(0.05);
Money discountedPrice = total.sub(discountAmount);
assertEquals("$95.00", discountedPrice.toString());
}
}
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然后，定义 WholeSaleOrder 类型。这个新对象是应用程序的核心：如果 WholeSaleOrder 类型配置了桶数、每桶价格和产品类型（季节性或全年性），就可以把它交给 PricingEngine，由后者确定对应的折扣并相应地在 WholeSaleOrder 实例中配置它。
WholesaleOrder 类的定义如清单 5 所示：
清单 5. WholesaleOrder 类
package org.acme.store.discount.engine;
import org.acme.store.Money;
public class WholesaleOrder {
private int numberOfCases;
private ProductType productType;
private Money pricePerCase;
private double discount;
public double getDiscount() {
return discount;
}
public void setDiscount(double discount) {
this.discount = discount;
}
public Money getCalculatedPrice() {
Money totalPrice = this.pricePerCase.mpy(this.numberOfCases);
Money tmpPrice = totalPrice.mpy(this.discount);
return totalPrice.sub(tmpPrice);
}
public Money getDiscountedDifference() {
Money totalPrice = this.pricePerCase.mpy(this.numberOfCases);
return totalPrice.sub(this.getCalculatedPrice());
}
public int getNumberOfCases() {
return numberOfCases;
}
public void setNumberOfCases(int numberOfCases) {
this.numberOfCases = numberOfCases;
}
public void setProductType(ProductType productType) {
this.productType = productType;
}
public String getProductType() {
return productType.getName();
}
public void setPricePerCase(Money pricePerCase) {
this.pricePerCase = pricePerCase;
}
public Money getPricePerCase() {
return pricePerCase;
}
}
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从清单 5 中可以看到，一旦在 WholeSaleOrder 实例中设置了折扣，就可以通过分别调用 getCalculatedPrice 和 getDiscountedDifference 方法得到折扣价格和节省的钱。
定义了 Money 和 WholesaleOrder 类之后，还要编写 JUnit 测试来验证 getCalculatedPrice 和 getDiscountedDifference 方法的功能。测试如清单 6 所示：
清单 6. JUnit 的 WholesaleOrderTest 类
package org.acme.store.discount.engine.junit;
import junit.framework.TestCase;
import org.acme.store.Money;
import org.acme.store.discount.engine.WholesaleOrder;
public class WholesaleOrderTest extends TestCase {
/*
* Test method for 'WholesaleOrder.getCalculatedPrice()'
*/
public void testGetCalculatedPrice() {
WholesaleOrder order = new WholesaleOrder();
order.setDiscount(0.05);
order.setNumberOfCases(10);
order.setPricePerCase(new Money(10.00));
assertEquals("$95.00", order.getCalculatedPrice().toString());
}
/*
* Test method for 'WholesaleOrder.getDiscountedDifference()'
*/
public void testGetDiscountedDifference() {
WholesaleOrder order = new WholesaleOrder();
order.setDiscount(0.05);
order.setNumberOfCases(10);
order.setPricePerCase(new Money(10.00));
assertEquals("$5.00", order.getDiscountedDifference().toString());
}
}
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