just don't upload it when you upload the applet. and you can edit the html to remove the link.

that said, sharing code is good.

opening the jar files you get compiled class files, its not the same as the pdes he is talking about.
you cant just easily copy and paste the code from there.

The exe generated by Processing is just a small launcher accessing the jars. And it isn't usable for an applet.

And, yes, I know at least two decompilers able to show Java source out of .class files (Jad and JD).
One can use ProGuard to obfuscate the code, but the result of decompiling it might be as readable (or better: good indentation!) as some code I see on this forum...
And as kooogy said, Processing is also about sharing, if you don't want to share (which is your right!), the only reliable way is... to keep everything private!

Isnt there a way how to hide source code (or if you now minecraft making server passwords to enter)

" if you now minecraft making server passwords to enter"
I don't know well Minecraft, but it is probably unrelated to this problem. If code is on server, you just don't have access to the source code.
But applets run on the user's computer, so you have to put the compiled code there. And as written above, there is no perfect way to hide the code, only ways to make it harder to fetch.

There are tools to obfuscate JavaScript, it makes code harder to read. But then, you have to write your Processing code all in pure JavaScript, I think.