How to solve java.lang.StackOverflowError in MVC design pattern (plus mySQL) -

i'm using mvc design pattern, , i'm complete beginner in design pattern , java. if didn't put loginmodel login = new loginmodel()); java.lang.nullpointerexception pop up. when put it, java.lang.stackoverflowerror happens. i'm not sure if give enough details, if need more, mention, i'll provide more details..

public class loginmodel {      private string username;     private int id;     private string email;     private long starttime;     private long endtime;     timer timer;      private javax.swing.jtextfield jtextfield1;     private javax.swing.jtextfield jtextfield2;      connection conn = null;     resultset rs = null;     preparedstatement pst = null;     loginmodel login = new loginmodel(); //this error happens       public loginmodel(){}     public loginmodel(int id,string username,string email){         this.id=id;         this.username=username;         this.email=email;             }      public int getid(){         return id;     }     public string getusername(){         return username;     }     public string getemail(){         return email;     }       public void setstarttime(long time){         starttime=time;     }     public void setendtime(long time){         endtime = time;     }     public long getusedtime(){         return (endtime-starttime);     }     public loginmodel(int seconds) {         timer = new timer();         timer.schedule(new loginmodel.remindtask(), seconds*1000);     }     public void settimer(int seconds){         timer = new timer();         timer.schedule(new loginmodel.remindtask(), seconds*1000);     }        class remindtask extends timertask {         public void run() {             joptionpane.showmessagedialog(null, "60 seconds left!");             timer.cancel();          }     }        public void retrievedbase (connection conn){     string sql = "select * customer_info username = ? , password = ?";     string sql2 = "select * admin_info username = ? , password = ?";     string sql11 = "select * customer_info username = ? , password = ? , paidremainingtime != 0";      try{         pst = conn.preparestatement(sql);         pst.setstring(1, jtextfield1.gettext());         pst.setstring(2, jtextfield2.gettext());         rs = pst.executequery();          if (rs.next()){         joptionpane.showmessagedialog(null, "welcome "+jtextfield1.gettext());             try{                  pst = conn.preparestatement(sql11);                  pst.setstring(1, jtextfield1.gettext());                  pst.setstring(2, jtextfield2.gettext());                  rs = pst.executequery();                   if (rs.next()){                       new dummyhomepage().setvisible(true);                     //this.setvisible(false);                      joptionpane.showmessagedialog(null,"your paid time remains "                              + rs.getint("paidremainingtime")+"minutes");                                          login.settimer(rs.getint("paidremainingtime"));                     long starttime = system.currenttimemillis( );                     login.setstarttime(starttime);              }                   else{                       new purchaseinterface().setvisible(true);                      //this.setvisible(false);              }             }             catch (exception e){             joptionpane.showmessagedialog(null, e);             }          }         else               try{                     pst = conn.preparestatement(sql2);                     pst.setstring(1, jtextfield1.gettext());                     pst.setstring(2, jtextfield2.gettext());                     rs = pst.executequery();             if (rs.next()){             joptionpane.showmessagedialog(null, "welcome admin "+jtextfield1.gettext());             new manageuserinterface().setvisible(true);              //this.setvisible(false);             }             else             joptionpane.showmessagedialog(null, "invalid username , password");                 }     catch (exception e){         joptionpane.showmessagedialog(null, e);     }     }      catch (exception e){         joptionpane.showmessagedialog(null, e);     }      }      public connection getdbase(){         return conn;     } } 

loginmodel login = new loginmodel(); 

login member variable in case, means it'll created every new object of type loginmodel.

since creating loginmodel object creates member variable login loginmodel, creates member variable login loginmodel... have problem.