Java JFrame Window not appearing when run from Eclipse

macOS + Eclipse + swt.jar gives this issue.

Turns out, in macOS, Eclipse adds a special argument -XstartOnFirstThread when starting the GUI app if you have swt.jar in the classpath. After removing swt.jar from external libraries (used to build classpath), problem solved.

It turns out I had a library problem. I had had imported all the jars in the .lib directory from jfreechart. In reality only two were needed and some unnecessary ones were labeled swt and experimental. Once I removed all the ones that were not needed, did a clean, and rebuilt, everything worked fine.

Oddly, changing the order of the jfreechart library (which included the conflicting jars) to the bottom did not help, the extra jars had to be removed.

Not a jfreechart issue, obviously my own library import issue. If you run into this I suggest you try to remove some of the libraries that may be conflicting, then clean, build, and run again.

Thanks to Hovercraft Full Of Eels and everyone else who responded for helping me out.