Hi CHandresh,
You can find the Javadoc at apidocs.rnd.mendix.com or in the directory you in which installed Mendix (for example, C:\Program Files\Mendix\9.0.0\runtime\javadoc).
Here’s a breif Java Api Doc also
https://docs.mendix.com/howto/logic-business-rules/java-api-tutorial/
Hope it helps !