public Instance output() throws Exception {
public Instance output() {
  public Instance output() throws Exception {    if (m_OutputFormat == null) {      throw new Exception("No output instance format defined");    }    if (m_OutputQueue.empty()) {      return null;    }    Instance result = (Instance)m_OutputQueue.pop();    // Clear out references to old strings occasionally    if (m_OutputQueue.empty() && m_NewBatch &&         (m_OutputFormat.numInstances() >= 20)) {      if (m_OutputStringAtts.length > 0) {        m_OutputFormat = m_OutputFormat.stringFreeStructure();      } else {        // m_OutputFormat.delete() isn't safe here        m_OutputFormat = new Instances(m_OutputFormat, 0);      }    }    return result;  }