src/net/java/sip/communicator/service/protocol/CallConference.java
/**
     * Adds a <tt>CallChangeListener</tt> to the <tt>Call</tt>s participating in
     * this telephony conference. The method is a convenience that takes on the
     * responsibility of tracking the <tt>Call</tt>s that get added/removed
     * to/from this telephony conference.
     *
     * @param listener the <tt>CallChangeListner</tt> to be added to the
     * <tt>Call</tt>s participating in this telephony conference
     * @throws NullPointerException if <tt>listener</tt> is <tt>null</tt>
     */
Adds a CallChangeListener to the Calls participating in
this telephony conference. The method is a convenience that takes on the
responsibility of tracking the Calls that get added/removed
to/from this telephony conference.

@param listener the CallChangeListner to be added to the
Calls participating in this telephony conference
@throws NullPointerException if listener is null
Adds a CallChangeListener to the Calls participating in this telephony conference . The method is a convenience that takes on the responsibility of tracking the Calls that get added / removed to / from this telephony conference . @param listener the CallChangeListner to be added to the Calls participating in this telephony conference @throws NullPointerException if listener is null
public void addCallChangeListener(CallChangeListener listener)
    {
        if (listener == null)
            throw new NullPointerException("listener");
        else
        {
            synchronized (callChangeListeners)
            {
                if (!callChangeListeners.contains(listener))
                    callChangeListeners.add(listener);
            }
        }
    }
public void addCallChangeListener ( CallChangeListener listener ) { if ( listener == null ) throw new NullPointerException ( "listener" ) ; else { synchronized ( callChangeListeners ) { if ( ! callChangeListeners . contains ( listener ) ) callChangeListeners . add ( listener ) ; } } }
Adds a <tt>CallChangeListener</tt> to the <tt>Call</tt>s participating in
 this telephony conference.
Adds a <tt > CallChangeListener< / tt > to the <tt > Call< / tt > s participating in this telephony conference .