Review

class FieldsWriter {
    final void addDocument(Document doc) throws IOException {
        indexStream.writeLong(fieldsStream.getFilePointer());

        int storedCount = 0;
        Iterator fieldIterator = doc.getFields().iterator();
        while (fieldIterator.hasNext()) {
            Fieldable field = (Fieldable) fieldIterator.next();
            if (field.isStored())
                storedCount++;
        }
        fieldsStream.writeVInt(storedCount);

        fieldIterator = doc.getFields().iterator();
        while (fieldIterator.hasNext()) {
            Fieldable field = (Fieldable) fieldIterator.next();
            if (field.isStored())
              writeField(fieldInfos.fieldInfo(field.name()), field);
        }
    }

}