I am writing an Android application using Eclipse. When I click on the project in the left tree view and then click debug, the IDE builds an APK and installs in the emulator
In eclipse, you can set in workspace preferences / run-debug / launching to always launch the previously launched application (until you explicitly choose an other application: then it will be the last that will be launched).
This way, no matter where you press (ctrl)F11 or click the debug/run button, the launch configuration you used the last time will be called again.
You will still be able to launch different applications of course, by explicitly calling their launchers (the way you debug now).