方法级别的抽象

//修改前
public class Customer
{
    public string FirstName { get; set; }
    public string SecondName { get; set; }
    public bool IsPriorityCustomer { get; set; }
    public decimal AnnualIncome { get; set; }
}
public class ProspectiveCustomer
{
    public string FirstName { get; set; }
    public string SecondName { get; set; }
    public decimal AnnualIncome { get; set; }
}

public class ProspectiveCustomerValidator
{
    public Customer CreateValidatedCustomer(
    ProspectiveCustomer prospectiveCustomer)
    {
        if (string.IsNullOrWhiteSpace(
        prospectiveCustomer.FirstName))
        {
            throw new ArgumentException("Invalid FirstName");
        }
        if (string.IsNullOrWhiteSpace(
        prospectiveCustomer.SecondName))
        {
            throw new ArgumentException("Invalid SecondName");
        }
        var newValidCustomer = new Customer
        {
            FirstName = prospectiveCustomer.FirstName,
            SecondName = prospectiveCustomer.SecondName
        };
        if (prospectiveCustomer.AnnualIncome > 100000)
        {
            newValidCustomer.IsPriorityCustomer = true;
        }
        return newValidCustomer;
    }
}

//修改后
using System;

public class Customer
{
    public string FirstName { get; set; }
    public string SecondName { get; set; }
    public bool IsPriorityCustomer { get; set; }
    public decimal AnnualIncome { get; set; }
}
public class ProspectiveCustomer
{
    public string FirstName { get; set; }
    public string SecondName { get; set; }
    public decimal AnnualIncome { get; set; }
}
public class ProspectiveCustomerValidator
{
    // Higher abstraction level
    public Customer CreateValidatedCustomer(
    ProspectiveCustomer prospectiveCustomer)
    {
        EnsureValidDetails(prospectiveCustomer);
        var validatedCustomer =
        CreateNewCustomerFrom(prospectiveCustomer);
        SetCustomerPriority(validatedCustomer);
        return validatedCustomer;
    }
    // Medium abstraction level
    private static void EnsureValidDetails(
    ProspectiveCustomer prospectiveCustomer)
    {
        EnsureValidFirstName(prospectiveCustomer);
        EnsureValidSecondName(prospectiveCustomer);
    }

    private static Customer CreateNewCustomerFrom(
    ProspectiveCustomer prospectiveCustomer)
    {
        return new Customer
        {
            FirstName = prospectiveCustomer.FirstName,
            SecondName = prospectiveCustomer.SecondName,
            AnnualIncome = prospectiveCustomer.AnnualIncome
        };
    }
    // Low abstraction level
    private static void EnsureValidFirstName(
    ProspectiveCustomer prospectiveCustomer)
    {
        if (string.IsNullOrWhiteSpace(prospectiveCustomer.FirstName))
        {
            throw new ArgumentException("Invalid FirstName");
        }
    }
    private static void EnsureValidSecondName(
    ProspectiveCustomer prospectiveCustomer)
    {
        if (string.IsNullOrWhiteSpace(
        prospectiveCustomer.SecondName))
        {
            throw new ArgumentException("Invalid SecondName");
        }
    }
    private static void SetCustomerPriority(Customer customer)
    {

        if (customer.AnnualIncome > 100000)
        {
            customer.IsPriorityCustomer = true;
        }
    }
}