C# 类（Class）
字段、属性、构造函数、静态成员、以及对象初始化器。
Key Points类是引用类型；构造函数保证对象一创建就是合法的。
定义一个类
C#
class Product
{
// 字段
private int _stock;
// 属性
public int Id { get; set; }
public string Name { get; set; } = "";
public decimal Price { get; set; }
// 计算属性
public bool InStock => _stock > 0;
// 构造函数
public Product(int id, string name, decimal price)
{
Id = id;
Name = name;
Price = price;
}
// 无参构造
public Product() : this(0, "未命名", 0m) { }
// 方法
public void Restock(int qty) => _stock += qty;
public override string ToString() => $"[{Id}] {Name} ￥{Price}";
}
var p = new Product(1, "键盘", 199m);
p.Restock(10);
Console.WriteLine(p);
Console.WriteLine(p.InStock);Output
[1] 键盘 ￥199
True对象初始化器
C#
class Config
{
public string Host { get; set; } = "localhost";
public int Port { get; set; } = 80;
public List<string> Tags { get; } = new();
}
var c = new Config
{
Host = "example.com",
Port = 8080,
Tags = { "web", "prod" } // 集合初始化器
};
Console.WriteLine($"{c.Host}:{c.Port} {string.Join(",", c.Tags)}");Output
example.com:8080 web,prodTags = { ... } calls Add on the existing collection; Tags = new List<string>{...} replaces it. Since Tags is get-only, only the former compiles.
静态成员
C#
class Counter
{
public static int Total { get; private set; }
public int Local { get; private set; }
public static Counter Create()
{
Total++;
return new Counter { Local = 1 };
}
static Counter() { Total = 0; } // 静态构造，只执行一次
}
Counter.Create();
Counter.Create();
Console.WriteLine(Counter.Total);Output
2继承与密封
C#
class Animal
{
public string Name { get; set; } = "";
public virtual string Speak() => "...";
}
class Dog : Animal
{
public override string Speak() => "汪汪";
}
// sealed：不能再被继承
sealed class Puppy : Dog
{
public override string Speak() => "嗷嗷";
}
Animal[] animals = { new Animal { Name = "?" }, new Dog { Name = "旺财" }, new Puppy { Name = "小旺" } };
foreach (var a in animals)
{
Console.WriteLine($"{a.Name}: {a.Speak()}");
}Output
?: ...
旺财: 汪汪
小旺: 嗷嗷virtual allows overriding, override overrides, sealed stops it. Methods in C# are not overridable by default (unlike Java) and need explicit virtual — safer, since changing a base class cannot silently alter subclasses.
成员一览
| Member | Example |
|---|---|
| 字段 | private int _x; |
| 属性 | public int X { get; set; } |
| 方法 | public void Run() |
| 构造函数 | public Foo() |
| 静态构造 | static Foo() |
| 索引器 | public T this[int i] |
| 事件 | public event EventHandler E; |
| 析构 | ~Foo()（少用） |
定义一个类
C#
class Product
{
// 字段
private int _stock;
// 属性
public int Id { get; set; }
public string Name { get; set; } = "";
public decimal Price { get; set; }
// 计算属性
public bool InStock => _stock > 0;
// 构造函数
public Product(int id, string name, decimal price)
{
Id = id;
Name = name;
Price = price;
}
// 无参构造
public Product() : this(0, "未命名", 0m) { }
// 方法
public void Restock(int qty) => _stock += qty;
public override string ToString() => $"[{Id}] {Name} ￥{Price}";
}
var p = new Product(1, "键盘", 199m);
p.Restock(10);
Console.WriteLine(p);
Console.WriteLine(p.InStock);Output
[1] 键盘 ￥199
True对象初始化器
C#
class Config
{
public string Host { get; set; } = "localhost";
public int Port { get; set; } = 80;
public List<string> Tags { get; } = new();
}
var c = new Config
{
Host = "example.com",
Port = 8080,
Tags = { "web", "prod" } // 集合初始化器
};
Console.WriteLine($"{c.Host}:{c.Port} {string.Join(",", c.Tags)}");Output
example.com:8080 web,prodTags = { ... } 和 Tags = new List<string> {...} 不同：前者调用已有的 Add，后者替换整个集合。因为 Tags 是只读属性，只能用前者。
静态成员
C#
class Counter
{
public static int Total { get; private set; }
public int Local { get; private set; }
public static Counter Create()
{
Total++;
return new Counter { Local = 1 };
}
static Counter() { Total = 0; } // 静态构造，只执行一次
}
Counter.Create();
Counter.Create();
Console.WriteLine(Counter.Total);Output
2继承与密封
C#
class Animal
{
public string Name { get; set; } = "";
public virtual string Speak() => "...";
}
class Dog : Animal
{
public override string Speak() => "汪汪";
}
// sealed：不能再被继承
sealed class Puppy : Dog
{
public override string Speak() => "嗷嗷";
}
Animal[] animals = { new Animal { Name = "?" }, new Dog { Name = "旺财" }, new Puppy { Name = "小旺" } };
foreach (var a in animals)
{
Console.WriteLine($"{a.Name}: {a.Speak()}");
}Output
?: ...
旺财: 汪汪
小旺: 嗷嗷virtual 声明可被重写，override 重写，sealed 封死。C# 里方法默认不可重写（和 Java 相反），必须显式 virtual —— 这更安全，改父类不会意外改变子类行为。
成员一览
| 成员 | 例子 |
|---|---|
| 字段 | private int _x; |
| 属性 | public int X { get; set; } |
| 方法 | public void Run() |
| 构造函数 | public Foo() |
| 静态构造 | static Foo() |
| 索引器 | public T this[int i] |
| 事件 | public event EventHandler E; |
| 析构 | ~Foo()（少用） |