question: public synchronized < M extends MVMap < K , V > , K , V > M openMap ( String name , MVMap . MapBuilder < M , K , V > builder ) { checkOpen ( ) ; String x = meta . get ( "name." + name ) ; int id ; long root ; HashMap < String , Object > c ; M map ; if ( x != null ) { id = DataUtils . parseHexInt ( x ) ; @ SuppressWarnings ( "unchecked" ) M old = ( M ) maps . get ( id ) ; if ( old != null ) { return old ; } map = builder . create ( ) ; String config = meta . get ( MVMap . getMapKey ( id ) ) ; c = New . hashMap ( ) ; c . putAll ( DataUtils . parseMap ( config ) ) ; c . put ( "id" , id ) ; map . init ( this , c ) ; root = getRootPos ( meta , id ) ; } else { c = New . hashMap ( ) ; id = ++ lastMapId ; c . put ( "id" , id ) ; c . put ( "createVersion" , currentVersion ) ; map = builder . create ( ) ; map . init ( this , c ) ; markMetaChanged ( ) ; x = Integer . toHexString ( id ) ; meta . put ( MVMap . getMapKey ( id ) , map . asString ( name ) ) ; meta . put ( "name." + name , x ) ; root = 0 ; } map . setRootPos ( root , - 1 ) ; maps . put ( id , map ) ; return map ; }
target:  Open a map with the given builder. The map is automatically create if it does not yet exist. If a map with this name is already open, this map is returned.