Select For Update question

I would like to use a SELECT ... FOR UPDATE statement in my Java program
in order to lock some rows while I do some work on them. However either
I don't understand how to use the JDBC connection properly of the FOR
UPDATE construct doesn't work with the JDBC driver.

As a test case I built a small GUI with just one button. When I click
the button the following sql is executed:

"select * from test for update";

While the GUI is still open I open a psql console and I am capable of
manually updating the rows in the test table ... they are not locked as
I had hoped.

What is the proper way to use select .. for update with the JDC driver?
Can someone point me to some example or documentation?

Thanks,

Jean-Christian Imbeault