New to Java

Hi all,
I was a newbie in java programming. I wanna make application with java, but some of my friend told me that java application can make u're system run slow cause u have to import all the classes that u need for u're application.
I wanna ask is java programming is slow down system when I compile and run the application that made u're application that I've made respond slowly?? How to avoid this??

Thanks for u're help.
My regrards