Well java is too vast language for me, so i never tried to learn it.. but what i really like is java scripts, i mean if you know how to make java script then you can do lot of stuff on web hacking.
Here i found some java script, use it if you like View password behind asterisk
if any one have logged in to any account and after log out if his password still exist on password field in asterisk form , i mean if he has checked remember my password checkbox.
so type this script in address bar and you will get password in plain text.
i know there are lots of tools available to do that but did you bring every tools with you every time?
Just copy paste this code in address bar and you can calculate simple maths.put your calculation in () like (2+2)
This is just for fun.. at client side if you want to edit web page then copy paste this code in address bar and start editing. as you refresh page it will be in original form.