不明白构造函数这样的写法？

[junjun0310]

c#Code
public class Racer:IComparable,IFormattable
{
private string firstName;
private string lastName;
private string country;
public int wins;
public string FirstName
{
get{return firstName;}
set{firstName=value;}
}
public string LastName
{
get{return lastName;}
set{lastName=value;}
}
public string Country
{
get{return country;}
set{country=value;}
}
public int Wins
{
get { return wins; }
set { wins = value; }
}

public Racer():this(string.Empty,string.Empty,string.Empty)

{ }
public Racer(string firstName, string lastName, string country) : this(firstName, lastName, country, 0)
{ }
public Racer(string firstName, string lastName, string country, int wins)
{
this.firstName = firstName;
this.lastName = lastName;
this.country = country;
this.wins = wins;
}

}

[sjt000]

构造函数的重载只能使用this关键字来引用