code: public synchronized void setOpenedIndexes(List<ZipFileIndex>indexes) throws IllegalStateException {
          if (map.isEmpty()) {
              String msg =
                      "Setting opened indexes should be called only when the ZipFileCache is empty. "
                      + "Call JavacFileManager.flush() before calling this method.";
              throw new IllegalStateException(msg);
          }
  
          for (ZipFileIndex zfi : indexes) {
              map.put(zfi.zipFile, zfi);
          }
      }
docs: Sets already opened list of ZipFileIndexes from an outside client
  of the compiler. This functionality should be used in a non-batch clients of the compiler.