Web applets were a terrible experience all round. Downloaded JAR files usually just worked, though. The GUI looked odd because it wasn't using normal operating system controls, but in terms of performance it was no slower than any native program except for in the most extreme cases.
Java on the web was pretty terrible from beginning to end, but The Java Web could've worked.
Now that we have the web, we're moving back to the Javaverse in the form of apps (which, on Android, are actually Java(-like)). Every big website has one of those "for the full experience, download our app" banners. Other sites use WASM to bring back the Java applet days, now without third party plugin full of security holes. Google Docs renders to a virtual canvas in the browser in the same way an applet would've back in 2003, except it would've been able to open files directly from the file system.
And lo and behold, the new system is also a terrible experience.
> Google Docs renders to a virtual canvas in the browser in the same way an applet would've back in 2003, except it would've been able to open files directly from the file system.
I'd have said the situation back then was a bit better than that - a Java applet wouldn't have been able to access your filesystem by default, for instance.
Part of the benefit of Sun's Java was that the bytecode itself could be statically verified to only have good behaviour and the plugin would then sandbox what it could access at runtime. The plugin itself would obviously have had bugs - like all software - but it's not obvious to me that was intrinsically worse than having all that code as part of the browser (as we do now).
I'd contrast it with ActiveX and (I think), which was very free about what its applets could do (basically just Windows executable code, I think). Flash I'm less clear on the limitations of.
We have moved on in other ways, of course - browsers are architected to isolate processes more, including use of things like seccomp.
To be fair, Java Swing was my first GUI programming experience, and is still the best I had. For Desktop, fast iteration, no budget, and works anywhere, it's basically Swing or Electron.
but in terms of performance it was no slower than any native program except for in the most extreme cases.
Java applications were really slow, and certainly much slower than native programs, until HotSpot became the default in J2SE 1.3. It's distance history now, but I remember a lot of excitement about Java in 1996 (compile once) and then disappointment of how slow it was.
(After some iterations HotSpot became a really good JIT compiler.)
I remember trying to play Java applet games before broadband Internet was widely deployed - I soon gave up on waiting for the applet to download and played some other game, but it was great once broadband Internet became available (or I was using a computer at a big institution with fast Internet).
It wasn't a good experience.
In the meantime, computers became fast enough to run the modern web. The average phone can run tens of these web based wordpressors.