sun.jvm.hotspot.gc_implementation.g1.G1CollectedHeap doesn't override CollectedHeap::printOn, as a result CLHSDB's universe command returns "unknown subtype of CollectedHeap @ ..." instead of something like "Garbage-first heap @ ...":

$ $JAVA_HOME/bin/java -XX:+UseG1GC Test &
$ PID=$!
$ $JAVA_HOME/bin/java -cp $JAVA_HOME/lib/sa-jdi.jar sun.jvm.hotspot.CLHSDB <<EOF
attach $PID
universe
quit
EOF

hsdb> Attaching to process 26897, please wait...
hsdb> Heap Parameters:
unknown subtype of CollectedHeap @ 0x00007f6de4021d38 (0x0000000085000000,0x0000000100000000)
hsdb>


I've attached simple testcase.