How do i know which default settings are enabled for Sun JVM?

You can run with -XX:+PrintFlagsFinal to print the values of all flags at startup of the JVM.

Alternatively, you can use the jinfo tool to check the value of a flag in a running JVM:

> jinfo -flag UseCompressedOops 7364
-XX:+UseCompressedOops

Use jps to find the pid of the process.