Item 14:Utilize Constructor Chaining

由于C#不知参数的默认值，but constructor initializers allow one constructor to call another construcor.
所以经常出现一下这种形式的代码：

public class MyClass
public class MyClass
private ArratList _col;
private string _name;

public MyClass()
//编译器会自动添加额外的初始语句
commonConstructor(0,"");
}

public MyClass(int initial)
//编译器会自动添加额外的初始语句
commonConstrutor(initial,"");
}

public void commonConstrucot(int initial,string name)
//编译器会自动添加额外的初始语句
//处理代码
}
}