android - java.lang.RuntimeException: Unable to start activity ComponentInfo {...}: java.lang.NullPointerException -

when click go 1 activity another, have error:

java.lang.runtimeexception: unable start activity componentinfo {...}: java.lang.nullpointerexception

i missing method? please me understand did wrong, why see error?

my activity: zaselenie.java

import java.util.arraylist;  import android.app.activity; import android.database.cursor; import android.database.sqlite.sqlitedatabase; import android.os.bundle; import android.util.log; import android.widget.arrayadapter; import android.widget.spinner;  public class zaselenie extends activity {      contactdbmoy cqh;     kvartdb kdb;     sqlitedatabase sdb;      private long rowid;      spinner spzaselenie;      @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.zaselenie);      spzaselenie  = (spinner)findviewbyid(r.id.spzaselenie);      // Инициализируем наш класс-обёртку             cqh = new contactdbmoy(zaselenie.this);             kdb = new kvartdb(zaselenie.this);              // База нам нужна для записи и чтения             sdb = cqh.getwritabledatabase();             sdb = kdb.getwritabledatabase();              bundle extras = getintent().getextras();             rowid = extras.getlong(contactmain.rowid);                cursor cursorkvart = sdb.query(kvartdb.table_name, new string[] {                     kvartdb._id, kvartdb.name_column }, null, //                                                                     // columns                                                                     //                                                                     //                                                                     // clause                     null, // values clause                     null, // don't group rows                     null, // don't filter row groups                     null // sort order                     );               arraylist<string> labels = new arraylist<string>();             while (cursorkvart.movetonext()) {                 // column indices + values of columns                 int idkvart = cursorkvart.getint(cursorkvart.getcolumnindex(kvartdb._id));                 string namekvart = cursorkvart.getstring(cursorkvart.getcolumnindex(kvartdb.name_column));                 log.i("log_tag", "row " + idkvart + " has name " + namekvart);                        labels.add(namekvart);                     // creating adapter spinner                     arrayadapter<string> dataadapter = new arrayadapter<string>(this,                             android.r.layout.simple_spinner_item, labels);                      // drop down layout style - list view radio button                     dataadapter                             .setdropdownviewresource(android.r.layout.simple_spinner_dropdown_item);                     dataadapter.notifydatasetchanged();                      // attaching data adapter spinner                     spzaselenie.setadapter(dataadapter);             }             cursorkvart.close();      }      public zaselenie() {         // todo auto-generated constructor stub     }      @override     protected void onresume() {         super.onresume();      }      @override     protected void onstop() {         super.onstop();         // закрываем соединения с базой данных         sdb.close();         kdb.close();     } } 

logcat error:

03-06 12:04:43.802: e/androidruntime(20861): fatal exception: main 03-06 12:04:43.802: e/androidruntime(20861): java.lang.runtimeexception: unable start activity componentinfo{ru.zloyel.manager_sutochnoy_arendy_1/ru.zloyel.manager_sutochnoy_arendy_1.zaselenie}: java.lang.nullpointerexception 03-06 12:04:43.802: e/androidruntime(20861):    @ android.app.activitythread.performlaunchactivity(activitythread.java:2059) 03-06 12:04:43.802: e/androidruntime(20861):    @ android.app.activitythread.handlelaunchactivity(activitythread.java:2084) 03-06 12:04:43.802: e/androidruntime(20861):    @ android.app.activitythread.access$600(activitythread.java:130) 03-06 12:04:43.802: e/androidruntime(20861):    @ android.app.activitythread$h.handlemessage(activitythread.java:1195) 03-06 12:04:43.802: e/androidruntime(20861):    @ android.os.handler.dispatchmessage(handler.java:99) 03-06 12:04:43.802: e/androidruntime(20861):    @ android.os.looper.loop(looper.java:137) 03-06 12:04:43.802: e/androidruntime(20861):    @ android.app.activitythread.main(activitythread.java:4745) 03-06 12:04:43.802: e/androidruntime(20861):    @ java.lang.reflect.method.invokenative(native method) 03-06 12:04:43.802: e/androidruntime(20861):    @ java.lang.reflect.method.invoke(method.java:511) 03-06 12:04:43.802: e/androidruntime(20861):    @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:786) 03-06 12:04:43.802: e/androidruntime(20861):    @ com.android.internal.os.zygoteinit.main(zygoteinit.java:553) 03-06 12:04:43.802: e/androidruntime(20861):    @ dalvik.system.nativestart.main(native method) 03-06 12:04:43.802: e/androidruntime(20861): caused by: java.lang.nullpointerexception 03-06 12:04:43.802: e/androidruntime(20861):    @ ru.zloyel.manager_sutochnoy_arendy_1.zaselenie.oncreate(zaselenie.java:39) 03-06 12:04:43.802: e/androidruntime(20861):    @ android.app.activity.performcreate(activity.java:5008) 03-06 12:04:43.802: e/androidruntime(20861):    @ android.app.instrumentation.callactivityoncreate(instrumentation.java:1079) 03-06 12:04:43.802: e/androidruntime(20861):    @ android.app.activitythread.performlaunchactivity(activitythread.java:2023) 03-06 12:04:43.802: e/androidruntime(20861):    ... 11 more 

check extras isn't null below...

if(extras != null) {     rowid = extras.getlong(contactmain.rowid); } 

also check cursor object isn't null below...

if(cursorkvart != null && cursorkvart.getcount() > 0) {      while (cursorkvart.movetonext()) {          ......      }  }