Hi
It will first check row4.house_no is null or not, if null then it will assign blank values
If not null, it will check the legth of the house_no, if less than 40 no change
else
row4.house_no= row4.house_no.trim().substring(0,39) //take only the first 40 characters
as in java the numbering starts from 0 so the max should be 39
hope it clarifies you.