Anon blocks are “large” blocks allocated via malloc or mmap — see the manpages. As such, they have nothing to do with the Java heap (other than the fact that the entire heap should be stored in just such a block).
In my experience, thread stacks also use anon blocks. If you see a lot of anon blocks that all have the same size, and that size is 512k to 4Mb (the example below is repeated over a dozen times for a Tomcat process that I have running), that’s the likely cause. Depending on the program, you may have up to a few dozen of these; if you’re seeing thousands, it means you have a problem with threading.
b089f000 504K rwx-- [ anon ]
b091d000 12K ----- [ anon ]
b0920000 504K rwx-- [ anon ]
b099e000 12K ----- [ anon ]
b09a1000 504K rwx-- [ anon ]
b0a1f000 12K ----- [ anon ]
But that leaves a question: why are you using pmap to diagnose a Java memory issue?