I just tried to preview a .class file from projectx in F26 konqueror with this result.  Attempts to use other tools also fail, and el7 has a similar problem.  Google finds related complaints from Windows 10. Apparently the class I hoped to examine isn't there - but that's another story. Failed to extract plugin meta data from '/usr/lib64/qt5/plugins/kf5/parts/kjavaappletviewer.so' John P