GUI Bulder is good and usefull thing but it is also hard to implement.
I have another solution named "WtkxBrowser", I will explain:
The main idea is to make application which will display wtkx files same as
web browser displays html files. But it difference from web-browsers
such application should monitor changes in wtkx files.
So displaying content will be updated automatically, so it will be no need in "refresh" button.
Programmer may open wtkx file in wtkx-browser, and see how it looks like currently,
after that he can change content of some wtkx-file and switch back to browser where
changes will be displayed immediately. And once again, and again.
If some error in occured in wtkx content, then stacks trace will be displayed
I have developed demo application (I will attach zip with jar and sources, and screenshot),
It's sure not a production quality code. It's also partially developed on swing. But it is a demo.
Is it interesting?