For this discussion the actual app does not matter. I want to cover what I learned. First off I have been programming in Java for a number of years so this is not about Java programming.
1. If you know Java then Android programming feels pretty natural but there are enough differences that you can't make assumptions. I got burnt more than once.
2. Setting up the environment took more than I expected. Everything is out on the web and I was happy to find a lot of on-line support no matter my question. What took a bit was a lot to download for all the Android flavors from 14. to 2.2. I had a little issue finding the proper USB driver so I could debug on my actual phone.
3. Running directly on the phone is faster than using the emulator. Plus it really shows the experience as you use your finger instead of a mouse. When you drag small things around with the mouse they are easy to see, not so much with the finger. The emulator is pretty solid. I did not find differences between what the phone did and what the emulator did.
4. Eclipse is a really nice IDE. Drop files into the drawable directory and they show up as resource IDs automatically. It does have some issues. It did not install the app 100% of the times when I pressed the run button. Could be the phone's fault. I was not totally consistent in swiping to unlock and getting ready to run. I also had the IDE pause when using intellisense, very annoying.
5. The UI does not stop running when you show an alert dialog. Something you get used to in Swing. Not a big deal, once you know that you just code with it in mind and it does make sense. You don't want to freeze the UI waiting on the user.
6. Rectangle is left, top, right, bottom instead of x, y, width, height. Just something to remember.
7. Checkbox uses isChecked and setChecked. I had code to do isSelected and setSelected. The code compiled but did not do what I expected. Made an assumption. Never understood why Swing did not use the properly named methods. Glad Android does.
8. There is no Combobox but there is a Spinner. When I think Spinner I think numbers but the Android Spinner does the work of the Combobox and it does it just fine.
9. Strings belong in string resources, not in your code. I am familiar with this as the Java code I have written has been internationalized. Of course I was not doing that by default, I was hacking together code to make it work but in the end I moved all the strings into string resources.
10. The canvas is pretty powerful. All the features I needed were supported and well named.
11. Not all phones are equal. Different screen resolution being the big one. I have a new phone so I have a big screen. I set the emulator for a smaller screen. I need to tweak the code even more to fit as many screens as possible and to not leave dead space on big screens.
12. You have to draw a lot of icons. I had an icon in my drawable directory but it was not the one I would see on the phone. I had to drop special sized ones in each of the drawable directories to have the proper one to show up. Even at that the proper one only showed up under applications. I had put a short cut to my app on one of my screens but that icon did not change during the next app install. I had to remove it and re-add it to the screen to get it to change. Icons are not a standard Windows size - 256x256, 128x128, 64x64 but are 72x72, 48x48 and 36x36.
13. Playing sound is easy but they don't always play to the end. I need to figure out why that is happening. The API is really straight forward.
14. The amount of on-line information is impressive. The official Android help pages are a great starting point then I would use what I found there to find some solid example code. I was always able to find what I needed with minimal searching.
15. The preference system is simple. I needed to save the sound, flashing and theme settings. Find a quick sample and 5 minutes later it was in place.
16. The options dialog was harder than I thought it should be. This seems like something that nearly every app will need so I thought there would be base classes to handle it. I found what I needed on the web but I can see where we will not see standardized dialogs.
17. I love the menu button, something I wish the iTouch had, but I had to dig around to find images for that area. These images tend to be gray scale with an indented look. Not typical color icons. I wanted to stay consistent with t;he Android look so I found where they are hidden in the SDK samples.
18. I was worried the game would take a long time to write but I got it done in a few days. I had the game running in Swing so the engine was ready to roll. I took the game to a new level with themes and greatly improved graphics. I also put in a help system using a basic alert dialog. I never did a help system with the Swing version as I did not want to learn RoboHelp or some other HTML based help system. I really could have cheated like I did with Android, just never push myself to do it.
All in all I am very impressed with the Android platform. I am late to the game so others have done the hard stuff and published a ton of code samples for me to use. It appears the SDK team learned from various Swing mistakes and weirdness producing a cleaner API. I am sure I forgot a lot of other things I learned, this is just my first Android app and I don't consider the app done. It is fully functional but like any piece of art it never really feels done. I will have to choose a stopping point and release it one day.