This is almost certainly questionable programming rather than an issue with Java performance in general. Java is the language most beginning programmers start w

This is almost certainly questionable programming rather than an issue with Java performance in general. Java is the language most beginning programmers start with and they'll do things like create wildly inefficient methods that they proceed to call from the UI thread and so on. Additionally the most used Java UI library (Swing) is not exactly known for its snappiness. The JNI interface introduces overhead but certainly not anywhere near the sort of overhead that should result in UI rendering issues. Long story short, sluggish UIs are bad programming and not related to the programming language they were created in.