\begin{tikzpicture}
\umlemptyclass{A1}
\umlemptyclass[x=4, y=-3]{A2}
\umlassoc[geometry=-|-, arg1=arg1, mult1=mult1, pos1=0.1, align1=left, arg2=arg2, mult2=mult2, pos2=2.9, align2=right]{A1}{A2}
\end{tikzpicture}