(Scratch that, it's now OK, so long as it's a publicly available and downloadable app - will rewrite this answer.)
If you want this to run within a native desktop application - and not in a normal brower connecting to a web-app, though that could also be one way of doing it - you'll need to integrate an in-app browser component.
If you are planning on building this into a Java program, have a look at JDIC and or at integrating a rendering engine (like WebKit).
You can also look at:
Have you had the chance to take a look at GreatMaps?
It's a .NET control that can be used/embedded in .NET apps. It's compatible with all framework versions and supports many map providers and Google Maps is between them.