追逐代码质量: 决心采用 FIT

　　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。

　　Money 类

　　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());
  }
}

　　WholeSaleOrder 类

　　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;
  }	
}