public double getAverageXmitTime() { List copy; synchronized(xmit_times_history) { copy=xmit_times_history.copy(); } int size=copy.size(); long total=0L; for(Enumeration en=copy.elements(); en.hasMoreElements();) { Long val=(Long)en.nextElement(); total+=val.longValue(); } return size > 0? total / size : -1; }