public static < L , K > void addListener ( Map < K , ListenerList < L > > map , K key , L listener ) { ListenerList < L > list = map . get ( key ) ; if ( list == null ) { map . put ( key , list = new ListenerList < L > ( ) ) ; } list . add ( listener ) ; }
Adds a listener to the listener list in the supplied map . If no list exists one will be created and mapped to the supplied key .