code: @Override
      public boolean isAttached(Appender appender) {
          if (appenderList == null || appender == null)
              return false;
          Appender a;
          Iterator<Appender> it = appenderList.iterator();
          while (it.hasNext()) {
              a = (Appender) it.next();
              if (a == appender) {
                  return true;
              }
          }
          return false;
      }
docs: /*
  (non-Javadoc)
  
  @see
  org.apache.log4j.helpers.AppenderAttachableImpl#isAttached(org.apache
  .log4j.Appender)