In top press Shift-H which turns on Threads. The man page for top says:
-H : Threads toggle
Starts top with the last remembered 'H' state reversed. When
this toggle is On, all individual threads will be displayed.
Otherwise, top displays a summation of all threads in a
process.
From my top I see that the PID of the top thread is: 28938. And 28938 in HEX is 0x710A. Notice that in the stack dump, each thread has an nid which is in HEX. And it just so happens that 0x710A is the id of the thread:
"Thread-0" prio=10 tid=0x00007f9a98020000 nid=0x710a runnable [0x00007f9a9d846000]
java.lang.Thread.State: RUNNABLE
at sun.security.provider.DigestBase.engineReset(DigestBase.java:139)
at sun.security.provider.DigestBase.engineUpdate(DigestBase.java:104)
at java.security.MessageDigest$Delegate.engineUpdate(MessageDigest.java:538)
at java.security.MessageDigest.update(MessageDigest.java:293)
at sun.security.provider.SecureRandom.engineNextBytes(SecureRandom.java:197)
- locked <0x00007f9aa457e400> (a sun.security.provider.SecureRandom)
at sun.security.provider.NativePRNG$RandomIO.implNextBytes(NativePRNG.java:257)
- locked <0x00007f9aa457e708> (a java.lang.Object)
at sun.security.provider.NativePRNG$RandomIO.access$200(NativePRNG.java:108)
at sun.security.provider.NativePRNG.engineNextBytes(NativePRNG.java:97)
at java.security.SecureRandom.nextBytes(SecureRandom.java:433)
- locked <0x00007f9aa4582fc8> (a java.security.SecureRandom)
at java.util.UUID.randomUUID(UUID.java:162)
at HeavyThread.run(HeavyThread.java:27)
at java.lang.Thread.run(Thread.java:619)
And so you can confirm that the Thread which is running the HeavyThread class is consuming most cpu.
In read world situations, it will probably be a bunch of threads that consume some portion of CPU and these threads put together will lead to the java process using 100% CPU.
http://code.nomad-labs.com/2010/11/18/identifying-which-java-thread-is-consuming-most-cpu/