静态关键字

static 关键字意味着两件事：

1. 此值不会在对象之间发生变化，而是在整个类中发生变化
2. 静态属性和方法不需要实例。

public class Foo
{
    public Foo{
        Counter++;
        NonStaticCounter++;
    }

    public static int Counter { get; set; }
    public int NonStaticCounter { get; set; }
}

public class Program 
{
    static void Main(string[] args)
    {
        //Create an instance
        var foo1 = new Foo();
        Console.WriteLine(foo1.NonStaticCounter); //this will print "1"

        //Notice this next call doesn't access the instance but calls by the class name.
        Console.WriteLine(Foo.Counter); //this will also print "1"

        //Create a second instance
        var foo2 = new Foo();

        Console.WriteLine(foo2.NonStaticCounter); //this will print "1"

        Console.WriteLine(Foo.Counter); //this will now print "2"
        //The static property incremented on both instances and can persist for the whole class

    }
}