可以仅通过静态属性实例化子类

Question

假设我有以下课程:

public class Gender
{
    public readonly string Name { get; set;}
    public readonly char Abbreviation { get; set;} 
    public readonly string ChildName { get; set;}
    public readonly int Number { get; set;}

    public static Gender Male = new Gender { Name = "Male", Abbreviation = 'M', Number = 1, ChildName = "Boy" };
    public static Gender Female = new Gender { Name = "Female", Abbreviation = 'F', Number = 2, ChildName = "Girl" };
    public static Gender Unknown = new Gender { Name = "Unknown", Abbreviation = 'U', Number = 0, ChildName = "Unknown" };
}

除了之外,我怎么能通过任何其他方式将Gender类实例化为非法

Gender MyGender = Gender.Male

从而制作

Gender Spaghetti = new Gender{Name = "Spaghetti", Abbreviation = 'S', Number = 123, ChildName = "Angel Hair" }

在编译时抛出错误？

Answer 1

将private构造函数添加到Gender类:

public class Gender
{
    public readonly string Name { get; set;}
    public readonly char Abbreviation { get; set;} 
    public readonly string ChildName { get; set;}
    public readonly int Number { get; set;}

    private Gender()
    {
    }

    public static Gender Male = new Gender { Name = "Male", Abbreviation = 'M', Number = 1, ChildName = "Boy" };
    public static Gender Female = new Gender { Name = "Female", Abbreviation = 'F', Number = 2, ChildName = "Girl" };
    public static Gender Unknown = new Gender { Name = "Unknown", Abbreviation = 'U', Number = 0, ChildName = "Unknown" };
}

您也可以添加readonly到Male/ Female/ Unknown声明,以使以下代码不可能:

Gender.Male = Gender.Female;

Answer 2

给它一个私有构造函数:

public class Gender
{
    // ...

    private Gender() {  }
}

通常,如果没有定义构造函数,则编译器会创建一个没有参数的"默认构造函数".但如果你定义一个,那就没有默认值.如果那个是私人的,那个班级之外的任何东西都不能称之为.所以没有什么可以构建Gender除Gender自身之外的实例.