java - this code is giving me this error : Error: Could not find or load main class undefined -

i working on project on android studio , editing app , code giving me error. signin app

public void signin() {      showpdialog();      customrequest jsonreq = new customrequest(request.method.post, method_account_login, null,             new response.listener<jsonobject>() {                 @override                 public void onresponse(jsonobject response) {                      if (app.getinstance().authorize(response)) {                          if (app.getinstance().getstate() == account_state_enabled) {                              intent = new intent(getapplicationcontext(), mainactivity.class);                             startactivity(i);                              activitycompat.finishaffinity(loginactivity.this);                          } else {                              app.getinstance().logout();                             toast.maketext(loginactivity.this, gettext(r.string.msg_account_blocked), toast.length_short).show();                         }                      } else {                          toast.maketext(getapplicationcontext(), getstring(r.string.error_signin), toast.length_short).show();                     }                      hidepdialog();                 }             }, new response.errorlistener() {         @override         public void onerrorresponse(volleyerror error) {              toast.maketext(getapplicationcontext(), gettext(r.string.error_data_loading), toast.length_long).show();              hidepdialog();         }     }) {          @override         protected map<string, string> getparams() {             map<string, string> params = new hashmap<string, string>();             params.put("username", username);             params.put("password", password);             params.put("clientid", client_id);              return params;         }     };      app.getinstance().addtorequestqueue(jsonreq); }