Because IntelliJ does a lot of work. Similarly, Visual Studio is not usually slow but sometimes it will mysteriously become so slow as to become unusable, or at least that was true a few years ago when I spent a lot of time in it.
Visual Studio is a hosting environment for Resharper. And Resharper makes it awfully slow. IntelliJ compared to VS (even without Resharper) is like Emacs compared to IntelliJ.
IntelliJ is written in Swing, which 10 years ago was certainly slower than an alternative UI framework like SWT. Not sure if there is a noticeable difference nowadays.
With IntelliJ using Swing as a major vendor and showing its potential, is there a chance for getting a new developer community behind Swing/geom2d? Or is IntelliJ in the progress of migrating away to something else?
Asking because I'm having an old (but useful) Java2D diagramming app lying around that I'd maybe like to lift, but the lack of a future perspective for java2d and Swing always held me back on working on it. I don't even know if java.awt.geom can handle HiDPI these days. Would be a pity to loose it, since java 2d certainly is a useful programming model for these kind of apps; what's missing is commitment (by Oracle or other party) to it.
Why is this so, if Java is not inherently slow?
Sure JetBrains are some of the smartest developers around and yet their IDE is still slow.
I can't help but feel that Java is slow and problems with performance in something like IntelliJ do nothing to dispel that feeling.