@Override public int compareTo(Value o){
  if (o instanceof StringVal) {
    return str.compareTo(((StringVal)o).str);
  }
 else {
    return 0;
  }
}

@ Override public int compareTo ( Value o ) { if ( o instanceof StringVal ) { return str . compareTo ( ( ( StringVal ) o ) . str ) ; } else { return 0 ; } }
compares the string value to another value
