典型重构1 (接口)

析取类或接口

　　将一个类分割为更小、针对性更强的类；从中析取出一系列更精细的接口

public class InvoiceService
{
    public string CreateInvoice(Invoice invoice){...}
    public string ProcessPayment(Invoice invoice,double amount){...}
    public double GetAmountOwed(Invoice invoice){...}
    public double GetTotalAmountInvoiceLastFY(Customer customer){...}
    public double GetTotalAmountPaidLastFY(Customer customer){...}
}

该类执行了几个相关但却互相分离的功能，供系统的不同部分使用
通过析取该类的接口，对其进行重构

public interface IInvoiceCreatingService
{
    string CreateInvoice(Invoice invoice);
}

public interface IInvoicePaymentService
{
    string ProcessPayment(Invoice invoice,double amount);
    double GetAmountOwed(Invoice invoice);
}

public interface IInvoiceReportingService
{
    double GetTotalAmountInvoiceLastFY(Customer customer);
    double GetTotalAmountPaidLastFY(Customer customer);
}

重构结果：

public class InvoiceService:IInvoiceCreatingService,IInvoicePaymentService,IInvoiceReportingSrvice
{
    public string CreateInvoice(Invoice invoice){...}
    public string ProcessPayment(Invoice invoice,double amout){...}
    public double GetAmountOwed(Invoice invoice){...}
    public double GetToatlAmountInvoicedLastFY(Customer customer){...}
    public double GetTotalAmountPaidLastFY(Customer customer){...}
}