1、数据类型的进化
C#1中实现Product类型代码
public class Product
{
string name;
public string Name
{
get { return name; }
} decimal price;
public decimal Price
{
get { return price; }
} public Product(string name, decimal price)
{
this.name = name;
this.price = price;
} public static ArrayList GetSampleProducts()
{
ArrayList list = new ArrayList();
list.Add(new Product("West Side Story", 9.99m));
list.Add(new Product("Assassins", 14.99m));
list.Add(new Product("Frogs", 13.99m));
list.Add(new Product("Sweeney Todd", 10.99m));
return list; } public override string ToString()
{
return string.Format("{0}: {1}", name, price); } }
C#2中的强类型集合和私有的赋值方法
public class Product
{
string name;
public string Name
{
get { return name; }
private set { Name = value; } 私有的赋值方法
} decimal price;
public decimal Price
{
get { return price; }
private set { Price = value; }
}
//C#3:Product(){}
public Product(string name, decimal price)
{ Name = name;
Price = price;
}
public static List<Product>GetSampleProducts()
{
List<Product>list= new List<Product>();
list.Add(new Product("West Side Story", 9.99m));
list.Add(new Product("Assassins", 14.99m));
list.Add(new Product("Frogs", 13.99m));
list.Add(new Product("Sweeney Todd", 10.99m));
return list; } public override string ToString()
{
return string.Format("{0}: {1}", name, price); } }
C#3自动实现的属性和更简单的初始化
public class Product
{
public string Name { get; private set; }
public string Price { get; private set; } public Product(string name, decimal price)
{ Name = name;
Price = price;
} private Product()
{
} public static List<Product> GetSampleProducts()
{
return new List<Product>
{
new Product {Name = "West Side Story", Price = 9.99m},
new Product {Name = "Assassins", Price = 14.99m},
new Product {Name = "Frogs", Price = 13.99m},
new Product {Name = "Sweeney Todd", Price = 10.99m}
};
} public override string ToString()
{
return string.Format("{0}: {1}", Name, Price);
} }
C#4中命名实参
public class Product
{ public override string ToString()
{
return string.Format("{0}: {1}", name, price);
}
//C#4中的参数：尽管私有赋值不能被公共的改变，但如果要求它也不能被私有的改变，将会更加的清晰，在C#4中，我们用调用构造函数时指定实参的名称
readonly string name;
public string Name { get { return name; } }
return new List<Product>
{
new Product {name = "West Side Story", price = 9.99m},
new Product {name = "Assassins", price = 14.99m},
new Product {name = "Frogs", price = 13.99m},
new Product {name = "Sweeney Todd", price = 10.99m},
}; }
2、排序和过滤的演化
1、排序
C#1中使用IComparer对ArrayList进行排序
class ProductNameComparer : IComparer
{
public int Compare(object x, object y)
{
Product first = (Product)x;
Product second = (Product)y;
return first.Name.CompareTo(second.Name);
}
}
static void Main()
{
ArrayList products = Product.GetSampleProducts();
products.Sort(new ProductNameComparer());
foreach (Product product in products)
{
Console.WriteLine(product);
}
}
C#2中使用IComparer<product>对List<Product>进行排序
class ProductNameComparer : IComparer<Product>
{
public int Compare(Product x, Product y)
{
return x.Name.CompareTo(y.Name);
}
}
static void Main()
{
List<Product> products = Product.GetSampleProducts();
products.Sort(new ProductNameComparer());
foreach (Product product in products)
{
Console.WriteLine(product);
}
}
C#2中使用委托进行比较
/*
* C#2的方法1确实有了一定的改进，但是我们希望能直接指定要进行的标胶，就能开始对产品进行排序，而不需要实现一个接口来做这件事
* 下面它告诉sort方法如何用一个委托来比较俩个产品.省略了接口实现的代码和products.Sort(new ProductNameComparer());
* List<Product> products = Product.GetSampleProducts();
* products.Sort（delegate （Product x，Product y）
* {return x.Name.CompareTo(y.Name);}
* ）;
*/
C#3中使用lambda表达式进行比较
List<Product> products = Product.GetSampleProducts();
products.Sort(（x,y）=>x.Name.CompareTo(y.Name));
foreach（Product product in products）
{
console.writeline(product);
}
C#3还有另一种写法排序
foreach（Product product in product.OrderBy（p=>p.Name））
{
console.writeline(product);//通知轻松的按顺序打印名称，同时不必修改原产品列表
}
2、查询
循环、测试和打印（C#1）
ArrayList products = Product.GetSampleProducts();
foreach (Product product in products.Cast<Product>().Where(product => product.Price > 10m))
{
Console.WriteLine(product);
}
测试和打印分开进行（C#2）
List<Product> products =Product.GetSampleProducts();
Predicate<Product> test = delegate(Product p){ return p.Price > 10m;};
List<Product> matches=products.FindAll(test);
Action<Product> print=console.writeLine;
matches.ForEach(print);
测试和打印分开进行的另一个版本（C#2）
List<Product> products =Product.GetSampleProducts();
products.FindAll（delegate （Product p）{ return p.Price >;}）.ForEach(Console.WriteLine);
用lambda表达式来进行测试（c#3）
List<Product> products =Product.GetSampleProducts();
foreach（Product product in products.Where（p=>p.price>））
{
Console.WriteLine(product);
}
C#中使用Linq表达式
foreach (Product product in products.Cast<Product>().Where(product => product.Price > 10m))
{
Console.WriteLine(product);
}