simple java open stored matrix

Hi, i started to create my first java external. My problem is the following js code which works fine for me. but i didn't get it working in java external to open the read menue. i think its trivial but i need some advice, because i couldn't find any solution in the help. thanks
the js code is:
function read(){
var Readmatrix = new JitterMatrix(1,"float32");
Readmatrix.read();
...
}