Review

class FieldCacheRangeFilter.FieldCacheDocIdSet {
    public DocIdSetIterator iterator() throws IOException {
      // Synchronization needed because deleted docs BitVector
      // can change after call to hasDeletions until TermDocs creation.
      // We only use an iterator with termDocs, when this was requested (e.g. range contains 0)
      // and the index has deletions
      final TermDocs termDocs;
      synchronized(reader) {
        termDocs = isCacheable() ? null : reader.termDocs(null);
      }
      if (termDocs != null) {
        // a DocIdSetIterator using TermDocs to iterate valid docIds
        return new DocIdSetIterator() {
          private int doc = -1;
          
          /** @deprecated use {@link #nextDoc()} instead. */
          public boolean next() throws IOException {
            return nextDoc() != NO_MORE_DOCS;
          }
          
          /** @deprecated use {@link #advance(int)} instead. */
          public boolean skipTo(int target) throws IOException {
            return advance(target) != NO_MORE_DOCS;
          }

          /** @deprecated use {@link #docID()} instead. */
          public int doc() {
            return termDocs.doc();
          }
          
          public int docID() {
            return doc;
          }
          
          public int nextDoc() throws IOException {
            do {
              if (!termDocs.next())
                return doc = NO_MORE_DOCS;
            } while (!matchDoc(doc = termDocs.doc()));
            return doc;
          }
          
          public int advance(int target) throws IOException {
            if (!termDocs.skipTo(target))
              return doc = NO_MORE_DOCS;
            while (!matchDoc(doc = termDocs.doc())) { 
              if (!termDocs.next())
                return doc = NO_MORE_DOCS;
            }
            return doc;
          }
        };
      } else {
        // a DocIdSetIterator generating docIds by incrementing a variable -
        // this one can be used if there are no deletions are on the index
        return new DocIdSetIterator() {
          private int doc = -1;
          
          /** @deprecated use {@link #nextDoc()} instead. */
          public boolean next() throws IOException {
            return nextDoc() != NO_MORE_DOCS;
          }
          
          /** @deprecated use {@link #advance(int)} instead. */
          public boolean skipTo(int target) throws IOException {
            return advance(target) != NO_MORE_DOCS;
          }

          /** @deprecated use {@link #docID()} instead. */
          public int doc() {
            return doc;
          }

          public int docID() {
            return doc;
          }
          
          public int nextDoc() {
            try {
              do {
                doc++;
              } while (!matchDoc(doc));
              return doc;
            } catch (ArrayIndexOutOfBoundsException e) {
              return doc = NO_MORE_DOCS;
            }
          }
          
          public int advance(int target) {
            try {
              doc = target;
              while (!matchDoc(doc)) { 
                doc++;
              }
              return doc;
            } catch (ArrayIndexOutOfBoundsException e) {
              return doc = NO_MORE_DOCS;
            }
          }
        };
      }
    }

}