The precautions to be taken to output the class-wise statistical information is described as follows:

• For running Java process, if you execute the jheapprof command in which the -copygc option is set, you can try to execute the pre-statistical copy garbage collection. In this case, if a free space of the Tenured area is insufficient, the copy garbage collection might not be executed.
  When you cannot execute the copy garbage collection, the extended verbosegc information when garbage collection occurred is not output, even if you specify -XX:+HitachiVerboseGC in the JavaVM start option. Furthermore, an extended thread dump that contains the class-wise statistical information is output simultaneously when executing the garbage collection.
  
• For Java process where -XX:+PrintGCDetails is specified when starting the JavaVM, you can execute the jheapprof command in which -copygc option is set, for executing the pre-statistical copy garbage collection. In this case, a 'Full GC' is output in the garbage collection that is output by specifying -XX:+PrintGCDetails.