c# - Constructor not working as expected in Unity -

i'm trying create griddata data in update/awake function test. can't seem constructor working. i'm new csharp , unity. so, i'm bit stuck here.

griddata class

[system.serializable] public class griddata  {      [system.serializable]     public struct rowdata{         public float[] colum;      }     public static int numrows =30;     public static int numcolums =20;     public rowdata[] rows = new rowdata[numrows];        //     //constructor     public griddata(int x, int y){         numrows =y;         numcolums = x;         rowdata[] rows = new rowdata[numcolums];     } } 

factalmapdata class

using system.collections; using system.collections.generic; using unityengine;  public class fractalmapdata : monobehaviour {      public int gridwidth =20;     public int gridwhight =20;     public griddata fractalgrid ;        void update () {          //test         fractalgrid =new griddata(gridwidth,gridwhight);         debug.log ("row" + fractalgrid.rows.length); //object reference not set instance of object         debug.log ("colum" + fractalgrid.rows[0].colum.length);//object reference not set instance of object     } } 

you never initialize public float[] colum; anywhere in code.

as result, when invoke constructor, although correctly create initialized rows array, colum field of each rowdata instance has not been initialized , throw null reference exception when trying access length of collection.