java - Removing dynamically Objects from JPanel -

via jspinner want add , remove object "porta" ajpanel, works fine adding , when remove 1 object if try remove 2 or more objects doesn't work properly. code think issue related last element of vector on add object "porta":

 import javax.swing.jframe;  public class preparagara extends jframe {  public jspinner spinner; private jpanel panel_1,panel_2; private int spin; private int nporta = 1; private portap scorriporta,porta; final vector<portap> vp = new vector<portap>();  /**  * launch application.  */  /**  * create application.  */ public preparagara() {      initialize(); }  /**  * initialize contents of frame.  */ private void initialize() {      final jframe frame = new jframe();     frame.setvisible(true);     frame.setbounds(100, 100, 1000, 400);     frame.setdefaultcloseoperation(jframe.exit_on_close);     frame.getcontentpane().setlayout(new gridlayout(4, 1, 3, 3));       jmenubar menubar = new jmenubar();     frame.getcontentpane().add(menubar);      jmenu mngara = new jmenu("gara");     mngara.setfont(new font("courier new", font.bold, 30));     menubar.add(mngara);      panel_1 = new jpanel();     frame.getcontentpane().add(panel_1);     panel_1.setlayout(new flowlayout(flowlayout.left, 5, 5));      final jpanel panel_2 = new jpanel();     frame.getcontentpane().add(panel_2);     panel_2.setlayout(new flowlayout(flowlayout.left, 5, 5));       jmenuitem mntmporte = new jmenuitem("porte");     mntmporte.setfont(new font("segoe ui", font.plain, 20));     mntmporte.addactionlistener(new actionlistener() {         public void actionperformed(actionevent arg0) {               jlabel lbl = new jlabel();             lbl.settext("numero porte : ");             panel_1.add(lbl);               spinnernumbermodel sm =new spinnernumbermodel(0,0,30,1);             final jspinner spinner = new jspinner(sm);             panel_1.add(spinner);                    spinner.getfocuslisteners();             spin=0;             panel_1.revalidate();              spinner.addchangelistener(new changelistener() {                  @override                 public void statechanged(changeevent arg0) {                     int ora=(int) spinner.getvalue();                      if(spin<ora && spin<30){                          porta = new portap(nporta);                         panel_2.add(porta);                         nporta++;                         vp.add(porta);                         panel_2.revalidate();                       }else{                         //int = vp.size();                         panel_2.remove(vp.lastelement());                         //panel_2.remove(porta);                         vp.lastelement().remove(porta);                                                  nporta=nporta-1;                         //system.out.println(i);                         panel_2.revalidate();                         panel_2.repaint();                     }                  spin=ora;                 }});         }     });     mngara.add(mntmporte);      jmenuitem mntmgiudici = new jmenuitem("giudici");     mntmgiudici.setfont(new font("segoe ui", font.plain, 20));     mngara.add(mntmgiudici);      jmenu mndbase = new jmenu("dbase");     mndbase.setfont(new font("courier new", font.bold, 30));     menubar.add(mndbase);      jmenuitem mntmresetpenalit = new jmenuitem("reset penalit\u00e0");     mndbase.add(mntmresetpenalit);      jmenuitem mntmresetporte = new jmenuitem("reset porte");     mndbase.add(mntmresetporte);      jmenuitem mntmrestgiudici = new jmenuitem("reset giudici");     mntmrestgiudici.setactioncommand("reset giudici");     mndbase.add(mntmrestgiudici);      jmenu mnreturn = new jmenu("return");     mnreturn.setfont(new font("courier new", font.bold, 30));     menubar.add(mnreturn);      jmenuitem mntmchiudimenu = new jmenuitem("chiudi menu");     mnreturn.add(mntmchiudimenu);           jpanel panel = new jpanel();     frame.getcontentpane().add(panel);   }   } 

i've done this. first, recommend portion of panel intend change should separate sub-panel. , when update occurs, call initialize() on sub-panel data indicating should contain. rebuilding panel every time changes. make sure don't have holding onto old components (listeners , such), or else have memory leaks.

someone else may have better solution, cleanest have found works in swing.