Eclipse is an open-source (under the Eclipse Public License, or EPL) powerful IDE with tooling for various languages. It has a GTK+ user interface and is written in Java. As it is written in Java it is cross-platform and capable of running on Linux, MacOS and Windows. It is maintained and used by a large community of volunteers and companies.
Installation
It can be installed via merely running:
flatpak install org.eclipse.Java
You may also install it using Gnome Software or KDE Discover; look for Eclipse IDE for Java Developers.
Troubleshooting
See Eclipse on Flathub for bug reports and pull requests on the Flatpak manifest.
No Splashscreen Image
As the splash is stored as legacy BMP try
yum install gdk-pixbuf2-modules-extra
to fix it.
Contact
Most of the Fedora "free java" people hang out on #fedora-java on Freenode . There are also people on #classpath also on Freenode. Community around the Eclipse Linux Tools project is emerging now and developers are hanging out on #eclipse-linux on Freenode.