public int invalidateByPrefix(String prefix){
  int deleted=0;
  for (  String key : keys()) {
    if (key.startsWith(prefix)) {
      invalidate(key);
      deleted++;
    }
  }
  return deleted;
}

public int invalidateByPrefix ( String prefix ) { int deleted = 0 ; for ( String key : keys ( ) ) { if ( key . startsWith ( prefix ) ) { invalidate ( key ) ; deleted ++ ; } } return deleted ; }
invalidate all values that start with the given key prefix , returning number deleted .
