Number of dialogs is just one of many criteria, I UI reviewed the two approaches and they both have their pros & cons.

However, the Java FX approach seems to be better of the two for the following reasons: 

1) User can see the context the class is used in. 
2) Typically when adding code gradually, there is only 1-2 broken imports. In this case, it doesn't make the process any
longer. When a large piece of code is copy&pasted or a new project is opened, there are many broken imports, but user is
more likely not to be familiar with the code, so the context the class is used in is of even more importance (see point 1).

However, the current Java FX implementation has some problems which need to be addressed before it comes into general use:
a) the identifier imports are being fixed for is not clear. It needs to be highlighted in the text.  
b) the drop-down menu is sometimes shown beyond the editor boundary (when the identifier is on the last visible line)
c) after all imports are fixed, user should be returned to the original "frame" - they should see the same code area as
when they invoked the code.

Also discussed with msauer (adding to CC), responsible for the Java editor.

As a result, I suggest to close this issue as wontfix and create a new issue to Java to change their approach.

http://www.netbeans.org/issues/show_bug.cgi?id=156888