Hi
Suppose I have written a litter program in Eclipse, how can I export it to an apk file so as to transfer to my HTC Desire for testing?
Thanks
Once you run it on your android emulator it will automatically converted to .apk
Right click on your project and click Android Tools -> Export Signed Application Package or Export Unsigned Application Package.
If you choose signed package then you need to create a keystore. If you choose unsigned package, then you need to enable "Unknown sources" option from your phone in Settings->Applications menu.
Also you can use your phone as an emulator by connecting your phone to computer with USB.
Additional reading: Signing your applications and How to enable USB debugging on your Android phone