Example2.java

// MainActivity.java
public class MainActivity extends AppCompactActivity{
    public static String extra_item_id = "some item id";
    public static boolean extra_wanna_show = true;
  
    public static String getExtraItemId(){
      return extra_item_id;
    }
  
    public static boolean getExtraWannaShow(){
      return extra_wanna_show;
    }   
}

// SomeAwesomeAndHyperRealisticDetailActivity.java
public String EXTRA_ITEM_ID = MainActivity.getExtraItemId();
public boolean EXTRA_WANNA_SHOW = MainActivity.getExtraWannaShow();

....
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    ....
    if (EXTRA_ITEM_ID != null) {
        Log.i("The App", "Yayyyyyy!!!");
    } else {
        throw new IllegalStateException("Why god whyyyyy!!!!");
    }
    ....    
}