code: private void setOverride(final String key, final String value) {
      final boolean doSecurely = key.startsWith("_");
      final String fullKey = defaultEnvironment + "." + key;
      if (value != null) {
        final String oldValue = _getProperty("", key, null);
        if (value.equals(oldValue)) {
          // Same value, not really an override.
          if (doSecurely) {
            logger.warning("*** IGNORED  *** Ignoring redundant override " + fullKey + "=***PROTECTED***");
          } else {
            logger.warning("*** IGNORED  *** Ignoring redundant override " + fullKey + "='" + value + "'");
          }
        } else {
          logger.warning("*** OVERRIDE *** Setting override " + fullKey);
          if (doSecurely) {
            logger.warning("                 New value=***PROTECTED***");
            logger.warning("                 Old value='" + oldValue + "'");
          } else {
            logger.warning("                 New value='" + value + "'");
            logger.warning("                 Old value='" + oldValue + "'");
          }
          allProperties.setProperty(fullKey, value);
        }
      }
    }
docs: Replaces whatever was in the allProperties object, and clears the cache.