private final void initMatrix(){
  log.info("  init matrix...");
  Set<Id> zids=new HashSet<Id>();
  for (  Id zid : l2zMapping.values()) {
    zids.add(zid);
  }
  matrix.clear();
  for (  Id fzone : zids) {
    for (    Id tzone : zids) {
      String key=fzone.toString() + "," + tzone.toString();
      matrix.put(key,"");
    }
  }
  log.info("  done.");
}

private final void initMatrix ( ) { log . info ( "  init matrix..." ) ; Set < Id > zids = new HashSet < Id > ( ) ; for ( Id zid : l2zMapping . values ( ) ) { zids . add ( zid ) ; } matrix . clear ( ) ; for ( Id fzone : zids ) { for ( Id tzone : zids ) { String key = fzone . toString ( ) + "," + tzone . toString ( ) ; matrix . put ( key , "" ) ; } } log . info ( "  done." ) ; }
produces a map that has " fromzone , tozone " as key , and leaves the values open
