The hello world application is a traditional milestone for many beginning programmers. I reached that milestone for the Android platform today.
In order to install the development environment, I followed the installation instructions at developer.android.com. I decided to use Eclipse on my Ubuntu system. The install took awhile because several large packages had to be downloaded.
I then followed the Android hello world tutorial. The first time I ran the hello world application on the emulator, I did not see the expected output. So, I ran it again and got the following warning.
Warning: Activity not started, its current task has been brought to the
front public class
A google search found someone reporting a similar problem with an informative response on stackoverflow. Turns out all I needed to do was hit the back button on the emulator.