1、数据类型的进化
C#1中实现Product类型代码
1 public class Product
2 {
3 string name;
4 public string Name
5 {
6 get { return name; }
7 }
8
9 decimal price;
10 public decimal Price
11 {
12 get { return price; }
13 }
14
15 public Product(string name, decimal price)
16 {
17 this.name = name;
18 this.price = price;
19 }
20
21 public static ArrayList GetSampleProducts()
22 {
23 ArrayList list = new ArrayList();
24 list.Add(new Product("West Side Story", 9.99m));
25 list.Add(new Product("Assassins", 14.99m));
26 list.Add(new Product("Frogs", 13.99m));
27 list.Add(new Product("Sweeney Todd", 10.99m));
28 return list;
29
30 }
31
32 public override string ToString()
33 {
34 return string.Format("{0}: {1}", name, price);
35
36 }
37
38
39 }
C#2中的强类型集合和私有的赋值方法
1 public class Product
2 {
3 string name;
4 public string Name
5 {
6 get { return name; }
7 private set { Name = value; } 私有的赋值方法
8 }
9
10 decimal price;
11 public decimal Price
12 {
13 get { return price; }
14 private set { Price = value; }
15 }
16 //C#3:Product(){}
17 public Product(string name, decimal price)
18 {
19
20 Name = name;
21 Price = price;
22 }
23 public static List<Product>GetSampleProducts()
24 {
25 List<Product>list= new List<Product>();
26 list.Add(new Product("West Side Story", 9.99m));
27 list.Add(new Product("Assassins", 14.99m));
28 list.Add(new Product("Frogs", 13.99m));
29 list.Add(new Product("Sweeney Todd", 10.99m));
30 return list;
31
32 }
33
34 public override string ToString()
35 {
36 return string.Format("{0}: {1}", name, price);
37
38 }
39
40 }
C#3自动实现的属性和更简单的初始化
1 public class Product
2 {
3 public string Name { get; private set; }
4 public string Price { get; private set; }
5
6 public Product(string name, decimal price)
7 {
8
9 Name = name;
10 Price = price;
11 }
12
13 private Product()
14 {
15 }
16
17 public static List<Product> GetSampleProducts()
18 {
19 return new List<Product>
20 {
21 new Product {Name = "West Side Story", Price = 9.99m},
22 new Product {Name = "Assassins", Price = 14.99m},
23 new Product {Name = "Frogs", Price = 13.99m},
24 new Product {Name = "Sweeney Todd", Price = 10.99m}
25 };
26 }
27
28 public override string ToString()
29 {
30 return string.Format("{0}: {1}", Name, Price);
31 }
32
33 }
C#4中命名实参
1 public class Product
2 {
3
4 public override string ToString()
5 {
6 return string.Format("{0}: {1}", name, price);
7 }
8 //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
9 readonly string name;
10 public string Name { get { return name; } }
11 return new List<Product>
12 {
13 new Product {name = "West Side Story", price = 9.99m},
14 new Product {name = "Assassins", price = 14.99m},
15 new Product {name = "Frogs", price = 13.99m},
16 new Product {name = "Sweeney Todd", price = 10.99m},
17 };
18
19
20 }
2、排序和过滤的演化
1、排序
C#1中使用IComparer对ArrayList进行排序
1 class ProductNameComparer : IComparer
2 {
3 public int Compare(object x, object y)
4 {
5 Product first = (Product)x;
6 Product second = (Product)y;
7 return first.Name.CompareTo(second.Name);
8 }
9 }
10 static void Main()
11 {
12 ArrayList products = Product.GetSampleProducts();
13 products.Sort(new ProductNameComparer());
14 foreach (Product product in products)
15 {
16 Console.WriteLine(product);
17 }
18 }
C#2中使用IComparer<product>对List<Product>进行排序
1 class ProductNameComparer : IComparer<Product>
2 {
3 public int Compare(Product x, Product y)
4 {
5 return x.Name.CompareTo(y.Name);
6 }
7 }
8 static void Main()
9 {
10 List<Product> products = Product.GetSampleProducts();
11 products.Sort(new ProductNameComparer());
12 foreach (Product product in products)
13 {
14 Console.WriteLine(product);
15 }
16 }
C#2中使用委托进行比较
1 /*
2 * 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
3 * 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());
4 * List<Product> products = Product.GetSampleProducts();
5 * products.Sort（delegate （Product x，Product y）
6 * {return x.Name.CompareTo(y.Name);}
7 * ）;
8 */
C#3中使用lambda表达式进行比较
1 List<Product> products = Product.GetSampleProducts();
2 products.Sort(（x,y）=>x.Name.CompareTo(y.Name));
3 foreach（Product product in products）
4 {
5 console.writeline(product);
6 }
7 C#3还有另一种写法排序
8 foreach（Product product in product.OrderBy（p=>p.Name））
9 {
10 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
11 }
2、查询
循环、测试和打印（C#1）
1 ArrayList products = Product.GetSampleProducts();
2 foreach (Product product in products.Cast<Product>().Where(product => product.Price > 10m))
3 {
4 Console.WriteLine(product);
5 }
测试和打印分开进行（C#2）
1 List<Product> products =Product.GetSampleProducts();
2 Predicate<Product> test = delegate(Product p){ return p.Price > 10m;};
3 List<Product> matches=products.FindAll(test);
4 Action<Product> print=console.writeLine;
5 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 >10;}）.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>10））
{
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);
}
时间： 2024-10-15 20:25:28