How can I execute something just once per application start?

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SharedPreferences seems like ugly solution to me. It’s much more neat when you use application constructor for such purposes.

All you need is to use your own Application class, not default one.

public class MyApp extends Application {

    public MyApp() {
        // this method fires only once per application start. 
        // getApplicationContext returns null here

        Log.i("main", "Constructor fired");
    }

    @Override
    public void onCreate() {
        super.onCreate();    

        // this method fires once as well as constructor 
        // but also application has context here

        Log.i("main", "onCreate fired"); 
    }
}

Then you should register this class as your application class inside AndroidManifest.xml

<application android:label="@string/app_name" android:name=".MyApp"> <------- here
    <activity android:name="MyActivity"
              android:label="@string/app_name">
        <intent-filter>
            <action android:name="android.intent.action.MAIN"/>
            <category android:name="android.intent.category.LAUNCHER"/>
        </intent-filter>
    </activity>
</application>

You even can press Back button, so application go to background, and will not waste your processor resources, only memory resource, and then you can launch it again and constructor still not fire since application was not finished yet.

You can clear memory in Task Manager, so all applications will be closed and then relaunch your application to make sure that your initialization code fire again.

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