帮我看看下面的代码？

[czp]

为什么类的实例不能访问其实例字段？：
Type
TNj = record
njh: integer;
ydns: integer;
Njlx: integer;
njmc: string;
end;

TKs = record
ksmc: string;
ksh: integer;
kch: string;
end;

TNodeInf = class
private
fNj: TNj;
fKs: Tksary;

{ Private declarations }
public
// constructor Create(xqh,xqmc: string);
procedure SetNj(njmc: string; njh,ydns,Njlx: integer);
procedure SetKs(ksmc,kch: array of string; ksh: array of integer );

end;

implementation

procedure TNodeInf.SetNj(njmc: string; njh,ydns,Njlx: integer);
begin

fNj.njmc := njmc;
fnj.njh := njh;
fnj.ydns := ydns;
fnj.Njlx := Njlx;
end;
....

为什么我在建立该对象的实例后，通过其实例调用时：
NodeInfo.SetNj('dd',9,7,5) ;
总是Access violation at address 004862af in ...错误？