From Forum Nokia Wiki

If you need to optimize a Java ME game or application and you don't know where to optimize, you should use a Profiler as the ones in SDKs and you should try to take times over your code.

If you want to know how many milliseconds an algorithm takes to finish the task in one device, you should use this code:

long start, finish, duration;
start = System.currentTimeMillis();
 
   // here goes all the code to check
 
finish = System.currentTimeMillis();
duration = finish - start;