java - Fast method for adds the selected elements of a jlist in another jlist -

i must select many item jlist1 , add them in jlist2 when click them. have writed method jlist1 doesn't work:

private void jlist1valuechanged(javax.swing.event.listselectionevent evt) {                                         elenco[indice]=jlist1.getselectedvalue().tostring();     indice++;     jlist2.setlistdata(elenco); } 

i have java.lang.nullpointerexception. elenco string[]. what's best method this? thanks.

i have similar requirement , here working code

edit: pasting elaborated code.

list<string>selectedvalues = new arraylist<string>();  list<string> selected = jlist1.getselectedvalueslist(); //list hold selected values.  selectedvalues.addall(selected);      jlist2.setlistdata(selectedvalues.toarray(new string[0]));  list<string>remainingvalues = new linkedlist<>(); for(int index=0; index<jlist1.getmodel().getsize(); index++){     string str = jlist1.getmodel().getelementat(index);     if( ! selectedvalues.contains(str)){         remainingvalues.add(str);     } } //getremainingvalueslist() returns values remaining after selection jlis1.setlistdata(remainingvalues);