Thank you! Now, the UI looks great. 
Yes, there should be. I think it has something to do with /usr/lib64/jvm/java-1.6.0-openjdk-1.6.0/jre/lib/fontconfig.SuSE.properties. I have found something in the Archlinux Wiki: Java Runtime Environment fonts - ArchWiki
Somehow, the Lucida font is not delivered and not available in openSUSE (search with locate for lucida and I also search in the repos for it. No results.)
I already did. But they explain things with fontconfig.properties. But there would be a problem I thought, since every time SuSEconfig --module fonts was executed, it overwrites fontconfig.SuSE.properties. So, there has to be an other place where the fonts are configure. This must be somewhere in /etc/fonts but I couldn’t find the right place.
This is for programmers who program with Java not for users. 
It does not help if I change anything in Netbeans since this problem is not related with NetBeans. It’s and Java/openSUSE problem. The font seems to be missing. Now, after installing fetchmsfonts it works. It probably takes an alternative font. Arial or whatever is defined. But I’d rather take Linux fonts. I like DejaVu.
As said, not a NetBeans problem. This does not solve the problem, it only avoids them. I like to solve this problem. I don’t think I’m the only one who had this problem.
But thank you for your answer. At least, it looks much better than before. 