Question

I have a container which switches its main content between several screen-sized panes. I’m not using CardLayout, instead I’m using remove(previous); add(current); validate();

In this container I have data fields for each of these panes, which are initialized at startup so that I can easily just switch the reference between them.

My question:

If you remove the previous pane and add the new / current one, does the memory taken up by the previous pane’s instance object remain in memory?

Because I considered setting the previous pane to null and re-creating the current pane before adding it to the container in an attempt to lower memory usage, but wasn’t sure if it would actually make any difference.

Thanks. 🙂

EDIT: This isn’t actually my class but it demonstrates how I’m going about switching views:

public class ViewManager {

   public static final int VIEW_LOGIN = 0;
   public static final int VIEW_CALENDAR = 1;
   public static final int VIEW_HELP = 2;
   public static final int VIEW_SETTINGS = 3;
   public static final int VIEW_PREFERENCES = 4;
   public static final int VIEW_STATS = 5;

   private static LoginPane login = new LoginPane();
   private static CalendarView calendar = new CalendarView();
   private static HelpPane help = new HelpPane();
   private static SettingsPane accountSettings = new SettingsPane();
   private static PreferencesPane preferences = new PreferencesPane();
   private static StatsPane stats = new StatsPane();

   private static int previousView;

   private static Object [] views = {login, calendar, help, accountSettings, preferences, stats};

   // Without settings old views to null and re-creating incoming view request
   public static void switchTo(int currentView){
      if(currentView == previousView) return;

      MainFrame.getContent().remove(views[previousView]);
      MainFrame.getContent().add(views[currentView]);        
      MainFrame.getContent().validate();
   }

    // Settings to null and re-creating incoming view request
   public static void switchToNullify(int currentView){
      if(currentView == previousView) return;

      MainFrame.getContent().remove(views[previousView]);
      views[previousView] = null;

      if(currentView == VIEW_LOGIN)            views[VIEW_LOGIN] = new LoginPane();
      else if(currentView == VIEW_CALENDAR)    views[VIEW_CALENDAR] = new CalendarView();
      else if(currentView == VIEW_HELP)        views[VIEW_HELP] = new HelpPane();
      else if(currentView == VIEW_SETTINGS)    views[VIEW_ACCOUNT_SETTINGS] = new SettingsPane();
      else if(currentView == VIEW_PREFERENCES) views[VIEW_PREFERENCES] = new PreferencesPane();
      else if(currentView == VIEW_STATS)       views[VIEW_STATS] = new StatsPane();

      MainFrame.getContent().add(views[currentView]);
      MainFrame.getContent().validate();
   }
}

Answer 1

If you remove the previous pane and add the new / current one, does
the memory taken up by the previous pane’s instance object remain in
memory?

Yes, unless you remove all references to that object. Once you’ve done that, it’ll be eligible for garbage collection.

Because I considered setting the previous pane to null…

Good idea!