Here is an example of how java.util.Date
object is instantiated, with some constructor arguments:
$date = new Java("java.util.Date", 70, 9, 4);
Further, it says:
The new Java("java.util.Date", 70, 9, 4) call creates a new instance of the java.util.Date class using the java.util.Date(int year, int month, int day) constructor.
So, you could maybe try this:
$myObject = new Java("net.sf.jasperreports.engine.export.JRXlsExporter", param1, param2);