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
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