The direct replacements match the API - but not all behaviors are covered by the API, and so they may not work for your program. In particular, the replacement for java.util.Hashtable is NOT synchronized (that is the point!), although it is multi-threaded safe. If you rely on the undocumented synchronization behavior of the JDK Hashtable, your program may not work. Similarly, the iteration order is different between this version and the JDK version (this exact issue broke the SpecJBB benchmark when the iteration order was changed slightly (via using a slightly different hash function) between JDK rev's).
If you want to drop-in the non-blocking versions of Hashtable you'll need to alter your bootclasspath - these classes come directly from your JDK and so are found via the System loader before any class-path hacks can be done.
To replace the JDK implementation of Hashtable with a non-blocking version of Hashtable, add java_util_hashtable-1.1.2.jar to your java launch line:
java -Xbootclasspath/p:java_util_hashtable-1.1.2.jar my_app_goes_here
