Maybe you didn't install the same lib that him (The link that your provide are down),better to check out this one on sourceForge https://sourceforge.net/projects/jmapviewer/ .

Or if you want to use the source code you just need to take the entire project of what you need and put in on your project and just import in whenever you want/need.
You can compil by yourself too. (but try to avoid linking in actual java source files, this will make it harder for you to keep track of what is your code, and what is someone else's code, especially if you import a lot of projects).

Here a link to the source code of And here an link of your MapPolygonImpl .