code: public java.util.Set entrySet()
      {
          java.util.Set combinedSet = new java.util.HashSet();
          if (subMaps != null) {
              for (int i = 0; i < subMaps.length; i++) {
                  synchronized (subMaps[i]) {
                      combinedSet.addAll(subMaps[i].entrySet());
                  } // synchronized (subMap).
              }
          }
          return combinedSet;
  
      }
docs: /*
  (non-Javadoc)
  This implementation is thread safe because it makes a copy of the set under synchronized locks under the subMaps.
  
  @see java.util.Map#entrySet()