With Kaffe I get
$ kaffe -classpath .:/usr/share/java/hsqldb.jar Test
ERROR:
java.sql.SQLException: The database is already in use by another process: org.hsqldb.NIOLockFile@23eda0de[file =/home/peter/test/testdb.lck, exists=true, locked=false, valid=false, fl =null]:
at org.hsqldb.jdbc.jdbcUtil.sqlException (jdbcUtil.java:67)
at org.hsqldb.jdbc.jdbcConnection.<init> (jdbcConnection.java:2427)
at org.hsqldb.jdbcDriver.getConnection (jdbcDriver.java:188)
at org.hsqldb.jdbcDriver.connect (jdbcDriver.java:166)
at java.sql.DriverManager.getConnection (DriverManager.java:164)
at java.sql.DriverManager.getConnection (DriverManager.java:188)
at Test.main (Test.java:12)