Question

How can I find out from many class file that the particular file is the activity which was created at the time of creating the project?

Answer 1

There is must one Activity as Launcher.

 <intent-filter>
          <action android:name="android.intent.action.MAIN" />
          <category android:name="android.intent.category.LAUNCHER" />
 </intent-filter>

It need to define in AndroidManifest.xml so check your AndroidManifest.xml and you could see one launcher activity..

I seen your AndroidManifest.xml which you given link in this case may be DialtactsActivity or DialtactsContactsEntryActivity launcher activity