I am not an GIS expert but I need to implement a MGRS service in Java.
Basically it is very very similar to the problem originating from this
Google Answer:

http://answers.google.com/answers/threadview?id=562752

However I need a real implementation of such service. I have came up
with the Java Interface to illustrate the requirement. You answer must
implement this interface fully and pass few test case. Please ask
question if you have any problem. Thank you.

public interface MGRSService {

	public void setLatitude(double lat);
	public void setLongitude(double lon);
	public void setGridSize(double meter);
	
	// this method return current MGRS zone value
	// based on the specific squre size in meter
	// and the provided lat/lon vale
	public String getCurrentZone();
	
	// this method return all adjacent zone surrounding
	// the current zone. it should return an array of
	// 8 zones
	public abstract String[] getAdjacentZone();
	
	// this method verify if the input zone is adjacent
	// to the current zone
	public abstract boolean isAdjacent(String zoneInMRGS);
	
}