java - i cant adding item to my jcombobox from my database -

i've been trying hours insert data jcombobox , frustates me can please me find error

here's code

import java.awt.borderlayout; import java.awt.eventqueue;  import javax.swing.defaultlistmodel; import javax.swing.jframe; import javax.swing.joptionpane; import javax.swing.jpanel; import javax.swing.border.emptyborder; import javax.swing.jlabel; import javax.swing.jbutton;  import java.awt.gridlayout; import java.awt.font; import java.sql.sqlexception; import java.util.vector;  import javax.swing.jlist; import javax.swing.jtextfield; import javax.swing.jcombobox;  import java.awt.event.itemlistener; import java.awt.event.itemevent; import java.awt.event.actionlistener; import java.awt.event.actionevent;   public class staffeditdelete extends jframe {      private jpanel contentpane;     private jtextfield textfield;     private jtextfield textfield_1;     private jtextfield textfield_2;     private jtextfield textfield_3;     private jtextfield textfield_4;     private jtextfield textfield_5;      /**      * launch application.      */     public static void main(string[] args) {         eventqueue.invokelater(new runnable() {             public void run() {                 try {                     staffeditdelete frame = new staffeditdelete();                     frame.setvisible(true);                 } catch (exception e) {                     e.printstacktrace();                 }             }         });     }      /**      * create frame.      */      connect con;  //  string []alpha;     vector<string> alpha;     jcombobox combobox;      public staffeditdelete() {         settitle("staff");         setdefaultcloseoperation(jframe.dispose_on_close);         setbounds(100, 100, 450, 424);         contentpane = new jpanel();         contentpane.setborder(new emptyborder(5, 5, 5, 5));         setcontentpane(contentpane);         contentpane.setlayout(new borderlayout(0, 0));          jpanel panel = new jpanel();         contentpane.add(panel, borderlayout.north);          jlabel lblstaff = new jlabel("staff");         lblstaff.setfont(new font("times new roman", font.bold, 24));         panel.add(lblstaff);          jpanel panel_1 = new jpanel();         contentpane.add(panel_1, borderlayout.center);         panel_1.setlayout(new gridlayout(7, 2, 10, 10));          jlabel lblnewlabel = new jlabel("id");         panel_1.add(lblnewlabel);         con.rs = con.executequery("select * detail");         try {             while(con.rs.next())             {             //  system.out.println("true");                 combobox.additem(con.rs.getstring(1));             }         } catch (exception e2) {             // todo auto-generated catch block             e2.printstacktrace();         }          combobox = new jcombobox();         combobox.additemlistener(new itemlistener() {             public void itemstatechanged(itemevent e)              {                 string items = e.getsource().tostring();                 con.rs = con.executequery("select * staff [id staff ='"+items+"']");                 try {                     textfield.settext(con.rs.getstring(2));                     textfield_1.settext(con.rs.getstring(3));                     textfield_2.settext(con.rs.getstring(4));                     textfield_3.settext(con.rs.getstring(5));                     textfield_4.settext(con.rs.getstring(6));                     textfield_5.settext(con.rs.getstring(7));                 } catch (sqlexception e1) {                     // todo auto-generated catch block                     e1.printstacktrace();                 }             }         });         panel_1.add(combobox);          jlabel lblnewlabel_1 = new jlabel("nama");         panel_1.add(lblnewlabel_1);          textfield = new jtextfield();         panel_1.add(textfield);         textfield.setcolumns(10);          jlabel lblnewlabel_2 = new jlabel("alamat");         panel_1.add(lblnewlabel_2);          textfield_1 = new jtextfield();         panel_1.add(textfield_1);         textfield_1.setcolumns(10);          jlabel lblnewlabel_3 = new jlabel("nomor telepon");         panel_1.add(lblnewlabel_3);          textfield_2 = new jtextfield();         panel_1.add(textfield_2);         textfield_2.setcolumns(10);          jlabel lblnewlabel_4 = new jlabel("jabatan");         panel_1.add(lblnewlabel_4);          textfield_3 = new jtextfield();         panel_1.add(textfield_3);         textfield_3.setcolumns(10);          jlabel lblnewlabel_5 = new jlabel("password");         panel_1.add(lblnewlabel_5);          textfield_4 = new jtextfield();         panel_1.add(textfield_4);         textfield_4.setcolumns(10);          jlabel lblnewlabel_6 = new jlabel("gaji");         panel_1.add(lblnewlabel_6);          textfield_5 = new jtextfield();         panel_1.add(textfield_5);         textfield_5.setcolumns(10);          jpanel panel_2 = new jpanel();         contentpane.add(panel_2, borderlayout.south);          jbutton btnedit = new jbutton("edit");         btnedit.addactionlistener(new actionlistener() {             public void actionperformed(actionevent e) {                 if (cektelpon())                  {                     int reply = joptionpane.showconfirmdialog(null, "edit "+combobox.getselecteditem().tostring()+"?","edit?",joptionpane.yes_no_option);                     if (reply == joptionpane.yes_option)                      {                         con.executeupdatestaff(combobox.getselecteditem().tostring(), textfield.gettext(), textfield_1.gettext(), textfield_2.gettext(), textfield_3.gettext(), textfield_4.gettext(), textfield_5.gettext());                         joptionpane.showmessagedialog(null, "data berhasil di edit");                      }                 } else {                     joptionpane.showmessagedialog(null, "nomor telepon harus angka", "error", joptionpane.error_message);                 }             }         });         panel_2.add(btnedit);          jbutton btndelete = new jbutton("delete");         btndelete.addactionlistener(new actionlistener() {             public void actionperformed(actionevent e) {                 int reply = joptionpane.showconfirmdialog(null, "delete "+combobox.getselecteditem().tostring()+"?","delete?",joptionpane.yes_no_option);                 if(reply == joptionpane.yes_option)                 {                     con.executedeletestaff(combobox.getselecteditem().tostring());                     joptionpane.showmessagedialog(null, "data berhasil di delete");                  }             }         });         panel_2.add(btndelete);          jbutton btnreset = new jbutton("reset");         btnreset.addactionlistener(new actionlistener() {             public void actionperformed(actionevent e) {                 combobox.setselectedindex(0);                 con.rs = con.executequery("select * staff [id staff] = '"+ combobox.getselecteditem().tostring()+"'");                  try {                     textfield.settext(con.rs.getstring(2));                     textfield_1.settext(con.rs.getstring(3));                     textfield_2.settext(con.rs.getstring(4));                     textfield_3.settext(con.rs.getstring(5));                     textfield_4.settext(con.rs.getstring(6));                     textfield_5.settext(con.rs.getstring(7));                  } catch (sqlexception e1) {                     // todo auto-generated catch block                     e1.printstacktrace();                 }               }         });         panel_2.add(btnreset);          jbutton btncancel = new jbutton("cancel");         btncancel.addactionlistener(new actionlistener() {             public void actionperformed(actionevent e) {                 dispose();             }         });         panel_2.add(btncancel);     }       public boolean cektelpon()     {         int flag = 0;         (int =0 ;i < textfield_2.gettext().length();i++)         {             if (textfield_2.gettext().charat(i) == '0')              {                 flag ++;             }             if (textfield_2.gettext().charat(i) == '1')              {                 flag ++;             }             if (textfield_2.gettext().charat(i) == '2')              {                 flag ++;             }             if (textfield_2.gettext().charat(i) == '3')              {                 flag ++;             }             if (textfield_2.gettext().charat(i) == '4')              {                 flag ++;             }             if (textfield_2.gettext().charat(i) == '5')              {                 flag ++;             }             if (textfield_2.gettext().charat(i) == '6')              {                 flag ++;             }             if (textfield_2.gettext().charat(i) == '7')              {                 flag ++;             }             if (textfield_2.gettext().charat(i) == '8')              {                 flag ++;             }             if (textfield_2.gettext().charat(i) == '9')              {                 flag ++;             }         }          if (flag == 0)          {             return true;         } else          {             return false;         }     }  } 

here's error

java.lang.nullpointerexception  @ staffeditdelete.<init>(staffeditdelete.java:85)  @ staffeditdelete$1.run(staffeditdelete.java:44)  @ java.awt.event.invocationevent.dispatch(unknown source)  @ java.awt.eventqueue.dispatcheventimpl(unknown source)  @ java.awt.eventqueue.access$000(unknown source) @ java.awt.eventqueue$1.run(unknown source) @ java.awt.eventqueue$1.run(unknown source)   @ java.security.accesscontroller.doprivileged(native method)   @ java.security.accesscontrolcontext$1.dointersectionprivilege(unknown source)  @ java.awt.eventqueue.dispatchevent(unknown source)  @ java.awt.eventdispatchthread.pumponeeventforfilters(unknown source)  @ java.awt.eventdispatchthread.pumpeventsforfilter(unknown source)  @ java.awt.eventdispatchthread.pumpeventsforhierarchy(unknown source)  @ java.awt.eventdispatchthread.pumpevents(unknown source)  @ java.awt.eventdispatchthread.pumpevents(unknown source)  @ java.awt.eventdispatchthread.run(unknown source) 

ive trying hours please me find error in code

java.lang.nullpointerexception

at staffeditdelete.(staffeditdelete.java:85)

you initializing jcombobox after combobox object using. statement should before while loop using object.

 combobox = new jcombobox();  //should before block  try {         while(con.rs.next())         {         //  system.out.println("true");         //here using combobox. should initialized before statement.             combobox.additem(con.rs.getstring(1));         }     } catch (exception e2) {         // todo auto-generated catch block         e2.printstacktrace();     }//not after block 

and 1 more problem con object not created yet. check 1 also.

just @ statement.

  con.rs = con.executequery("select * detail"); 

what con , rs here.