I came across the sun.misc.Unsafe package the other day and was amazed at what it could do.
Of course, the class is undocumented, but I was wondering if there was ever a good reason to use it. What scenarios might arise where you would need to use it? How might it be used in a real-world scenario?
Furthermore, if you do need it, does that not indicate that something is probably wrong with your design?
Why does Java even include this class?
Based on a very brief analysis of the Java 1.6.12 library using eclipse for reference tracing, it seems as though every useful functionality of Unsafe is exposed in useful ways.
CAS operations are exposed through the Atomic* classes. Memory manipulations functions are exposed through DirectByteBuffer Sync instructions (park,unpark) are exposed through the AbstractQueuedSynchronizer which in turn is used by Lock implementations.
You need it if you need to replace functionality provided by one of the classes which uses it currently.
This can be custom/faster/more compact serialization/deserialization, a faster/larger buffer/resizable version of ByteBuffer, or adding an atomic variable e.g. one not supported currently.
I have used it for all of these at some time.