public StringDataType(String s,int len){
  if (len < s.length()) {
    this.s=s.substring(0,len);
  }
 else {
    this.s=String.format("%-" + len + "s",s);
  }
}

public StringDataType ( String s , int len ) { if ( len < s . length ( ) ) { this . s = s . substring ( 0 , len ) ; } else { this . s = String . format ( "%-" + len + "s" , s ) ; } }
construct a stringdatatype with length len and value s .
