public static final String MyPREFERENCES = "MyPrefs" ;
public static final String counterKey = "counterKey";

SharedPreferences sharedpreferences;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
    //doing basic stuff of set layout and all here...

    //Initialize sharedpreferences here
    sharedpreferences = getSharedPreferences(MyPREFERENCES, Context.MODE_PRIVATE);

    //call to increment counter here
    updateAppOpenCounter();

    //do remaining stuff here....
}

private void updateAppOpenCounter() {
    SharedPreferences.Editor editor = sharedpreferences.edit();

        editor.putInt(counterKey, getAppOpenedCount() + 1);
        editor.commit();
}

private int getAppOpenedCount() {
    sharedpreferences.getInt(counterKey, 0); //Kept 0 as default opened count if not set to shared yet.
}