from
web page
no arguments
Enables or disables assertions in all classes except system classes.
packageName...
Enables or disables assertions in the named package and any subpackages.
...
Enables or disables assertions in the unnamed package in the current working directory.
className
Enables or disables assertions in the named class
so java -da com.blah.MyClass <no arguments>
java -da:com.blah.MyClass <disables assertions in com.blah.MyClass class >