java - how to add items to a list box from another class in netbeans -

i add elements list box on jframe, different class doesn't seem work no matter try... not error or feedback on whats wrong this... heres layout have, listbox using defaultlistmodel lm2

i know how add elements jlist in jframe class, reason unable add elments class when adding inside jframe class:

  public void log(string str) {       lm2.addelement(str);     } 

and on "other class"

  frmmain doit = new frmmain();    doit.log("add list box"); 

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more details add- --- >

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i have 3 classes , here are:

frmmain.class

  // jframe class builds jframe (from jframe template)     public class frmmain extends javax.swing.jframe {          /** creates new form frmmain */         public frmmain() {             initcomponents();         }            public void log(string str) {           lm2.addelement(str);         }             public defaultlistmodel lm2 = new defaultlistmodel();     } 

requestinfo.class

// requestinfo.class, trying add item  // jlist doesn't add or error  public class requestinfo {    public void processreturnedinfo(string sdata, boolean bwithlabel) {               frmmain fm = new frmmain();             fm.log("test test");    } 

rs232example.class

     // main class sets jframe visible   public class rs232example {       public static void main(string[] args) throws exception {           frmmain form = new frmmain();         form.setvisible(true);      }    } 

i understand maybe need set form visible on requestinfo.class, can't this, because continuously open form multiple times, because class method called multiple times event...

if listbox-model set right (like listbox.setmodel(this.lm2);) guess following should work:

public static void main(string[] args) throws exception {   frmmain form = new frmmain();   form.setvisible(true);   form.log("hallo"); } 

if wondering why works , code within requestinfo not, keep in mind, create new frmmain it's own listmodel every call of processreturnedinfo

if want have 1 frame updated try use frame singleton:

change constructor of frmmain public private , add class:

private static frmmain instance = null;  public static frmmain getinstance() {   if (instance == null) {     instance = new frmmain();   }   return instance; } 

instead of calling new frmmain() must use frmmain.getinstance() in requestinfo , rs232example

that's how work on same frame.

good luck.