代碼如下:

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 
namespace Test 
{ 
class Program 
{ 
static void Main(string[] args) 
{ 
var customer = new Customer 
{ 
IsActive = true, 
LateFees = 100M, 
TotalRentNumber = 10 
}; 
Console.WriteLine(customer.CanRent()); 
Console.ReadKey(); 
} 
} 
public interface ISpecification<T> 
{ 
/// <summary> 
/// 是否可以租賃 
/// </summary> 
bool IsSatisfiedBy(T entity); 
/// <summary> 
/// 與操作 
/// </summary> 
ISpecification<T> And(ISpecification<T> other); 
/// <summary> 
/// 否操作 
/// </summary> 
ISpecification<T> Not(); 
} 
/// <summary> 
/// 基類 
/// </summary> 
public abstract class CompositeSpecification<T> : ISpecification<T> 
{ 
public abstract bool IsSatisfiedBy(T candidate); 
public ISpecification<T> And(ISpecification<T> other) 
{ 
return new AndSpecification<T>(this, other); 
} 
public ISpecification<T> Not() 
{ 
return new NotSpecification<T>(this); 
} 
} 
/// <summary> 
/// 與操作 
/// </summary> 
public class AndSpecification<T> : CompositeSpecification<T> 
{ 
private ISpecification<T> leftSpecification; 
private ISpecification<T> rightSpecification; 
public AndSpecification(ISpecification<T> leftSpecification, ISpecification<T> rightSpecification) 
{ 
this.leftSpecification = leftSpecification; 
this.rightSpecification = rightSpecification; 
} 
public override bool IsSatisfiedBy(T entity) 
{ 
return leftSpecification.IsSatisfiedBy(entity) && rightSpecification.IsSatisfiedBy(entity); 
} 
} 
///<summary> 
///否操作 
/// </summary> 
public class NotSpecification<T> : CompositeSpecification<T> 
{ 
private ISpecification<T> innerSpecification; 
public NotSpecification(ISpecification<T> innerSpecification) 
{ 
this.innerSpecification = innerSpecification; 
} 
public override bool IsSatisfiedBy(T entity) 
{ 
return !innerSpecification.IsSatisfiedBy(entity); 
} 
} 
/// <summary> 
/// 是否達(dá)到最大的規(guī)定租賃數(shù) 
/// </summary> 
public class HasReachedMaxSpecification : CompositeSpecification<Customer> 
{ 
public override bool IsSatisfiedBy(Customer entity) 
{ 
return entity.TotalRentNumber > 5; 
} 
} 
/// <summary> 
/// 是否激活 
/// </summary> 
public class CustomerActiveSpecification : CompositeSpecification<Customer> 
{ 
public override bool IsSatisfiedBy(Customer entity) 
{ 
return entity.IsActive; 
} 
} 
/// <summary> 
/// 是否欠費 
/// </summary> 
public class CustomerHasLateFeesSpecification : CompositeSpecification<Customer> 
{ 
public override bool IsSatisfiedBy(Customer entity) 
{ 
return entity.LateFees > 0; 
} 
} 
public class Customer 
{ 
private ISpecification<Customer> hasReachedRentalThreshold; 
private ISpecification<Customer> customerIsActive; 
private ISpecification<Customer> customerHasLateFees; 
public Customer() 
{ 
hasReachedRentalThreshold = new HasReachedMaxSpecification(); 
customerIsActive = new CustomerActiveSpecification(); 
customerHasLateFees = new CustomerHasLateFeesSpecification(); 
} 
/// <summary> 
/// 用戶租賃DVD數(shù)量 
/// </summary> 
public int TotalRentNumber 
{ 
get; 
set; 
} 
/// <summary> 
/// 賬戶是否激活 
/// </summary> 
public bool IsActive 
{ 
get; 
set; 
} 
/// <summary> 
/// 用戶之前是否還欠費 
/// </summary> 
public decimal LateFees 
{ 
get; 
set; 
} 
public bool CanRent() 
{ 
ISpecification<Customer> canRent = customerIsActive.And(hasReachedRentalThreshold.Not()).And(customerHasLateFees.Not()); 
return canRent.IsSatisfiedBy(this); 
} 
} 
}