I know of an FTP app where you can drag remote files to explorer. I guess it works using OLE DnD. This mechanism says that when initiating the drop the source app only says what type of thing gets dragged, so that another app can decide whether it wants the object. Only when the object is really dropped the source application must provide data, which gives it a chance to download the file and save it to a temporary location, where the target app then reads it from.

I once attended a presentation of a program that converted UML diagrams to Java code. It was very interesting to watch.
The thing generated a bunch of source files with nothing but class declarations and claimed it created 98% of the application's code

I don't know how they know what part of the final product they create, but the presentor was silently laughed at

What about gcc? Can't gcc compile java to native?

C or C++ emulators tend to have highly optimized inline assembly.
A pure C/C++ emulator is not likely to be that much faster than a Java one.