fetchsize dynamically changeable?

Given all the other requirements for cursors are met, is it possible to change
the fetchsize on the fly?

e.g.
conn.createStatement(...);
st.setFetchsize(1);
rs=st.executeQuery(...);//we got the first record
st.setFetchsize(10);
rs.next(); //now we got records nr. 2-11 in memory and sit at nr. 2

BTW - how is FETCH BACKWARD, what needs to be done to get it working?