multiplayer game - java2D

Hello all, urgent guidance required ??? i am developping a simple game using java with Graphics2D library.
the game involve moving of objects, object and its attribute are stored in a class : Piece

during the game every object involved in the game are stored within a 2D array. (every piece has a position atribute)
this is my 1st game and i need it to be able to allow two user moving diferent piece ON THE SAME PANEL.

if my thinking is good, i think i need to find a way to share the the 2D array and make it possible to access and modify the array at the same time.

i know a litle bit of socket programming, Gurus, share your wisdom with me. How should i proceed ? :-\