private String getCacheXmlFileName() {
    String cacheXmlFileName = getGemFireProperties().get(CACHE_XML_FILE);
    if (cacheXmlFileName == null) {
      cacheXmlFileName = getDefaultCacheXmlFileName();
    }
    return cacheXmlFileName;
  }
Instance reference which is set in static initialization blocks of any subclasses.
extensions/geode-modules/src/main/java/org/apache/geode/modules/session/bootstrap/AbstractCache.java