In Dbx 12.3, the "print" command used on any valid variable in debugger console after the breakpoint is hit is causing a hang.
The project was compiled in the same version, 12.3. The JDK used was 1.6.0_30.
This issue does not replicate with Dbx 12.2 (with code still compiled in 12.3).
Unfortunately, I wasn't able to reproduce your problem from the description. JDK you're using seems to be fine; the other usual suspect in these kinds of situations is pretty-printing feature of dbx (type 'help prettyprint' in the dbx console). Try to issu this command on the dbx console before printing anything and see if it helps:
dbxenv output_pretty_print off