As we run some Java servers such as Weblogic, Apache, Websphere, blah-blah, we need to use -D option.
Here is the command that is used to start up WebLogic

%JAVA_HOME%\bin\java -ms64m -mx64m -classpath %JAVA_CLASSPATH% -Dweblogic.class.path=%WEBLOGIC_CLASSPATH% -Dweblogic.home=. -Djava.security.manager -Djava.security.policy==.\weblogic.policy weblogic.Server

( I copied this from startWeblogic.cmd file).

Can you guys try to explain the secrets to the new Java graprammers?

If you are a Java verteran, I would be appreciated you
do this job. If you don't know things about _D, plese do not
do guess work.