android - E/AndroidRuntime(1549): java.lang.RuntimeException: Unable to start activity ComponentInfo: -

here modified code: but, still getting same error. please help, doing wrong.

public class mainactivity extends actionbaractivity {  int counter; button addone; button subone; textview display;  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);      addone=(button) findviewbyid(r.id.badd);     subone= (button) findviewbyid(r.id.bsub);     display =(textview) findviewbyid(r.id.tv1);     counter=0;       addone.setonclicklistener(new view.onclicklistener() {          @override         public void onclick(view arg0) {             // todo auto-generated method stub         counter++;         display.settext("counter is"+ counter);         }     });        subone.setonclicklistener(new view.onclicklistener() {          @override         public void onclick(view arg0) {             // todo auto-generated method stub             counter--;             display.settext("counter "+ counter);             //display.settext("counter is"+ counter);         }     });     } 

my xml code:

<linearlayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:id="@+id/linearlayout1" android:layout_width="match_parent" android:layout_height="match_parent" android:background="@drawable/bat" android:orientation="vertical" android:paddingbottom="@dimen/activity_vertical_margin" android:paddingleft="@dimen/activity_horizontal_margin" android:paddingright="@dimen/activity_horizontal_margin" android:paddingtop="@dimen/activity_vertical_margin" tools:context="com.iitb.practice.mainactivity$placeholderfragment" >  <textview     android:id="@+id/tv1"     android:layout_width="fill_parent"     android:layout_height="wrap_content"     android:layout_gravity="center"     android:gravity="center"     android:text="@string/total"     android:textsize="35sp" >  </textview>  <button     android:id="@+id/bsub"     android:layout_width="fill_parent"     android:layout_height="45dp"     android:text="@string/sub" />   <button      android:id="@+id/badd"      android:layout_width="fill_parent"      android:layout_height="45dp"      android:text="@string/add" /> 

i getting following error: logcat:

05-19 03:42:58.520: d/androidruntime(1281): shutting down vm 

05-19 03:42:58.520: w/dalvikvm(1281): threadid=1: thread exiting uncaught exception (group=0xb3a96ba8) 05-19 03:42:58.540: e/androidruntime(1281): fatal exception: main 05-19 03:42:58.540: e/androidruntime(1281): process: com.iitb.practice, pid: 1281 05-19 03:42:58.540: e/androidruntime(1281): java.lang.runtimeexception: unable start activity componentinfo{com.iitb.practice/com.iitb.practice.mainactivity}: java.lang.nullpointerexception 05-19 03:42:58.540: e/androidruntime(1281): @ android.app.activitythread.performlaunchactivity(activitythread.java:2195) 05-19 03:42:58.540: e/androidruntime(1281): @ android.app.activitythread.handlelaunchactivity(activitythread.java:2245) 05-19 03:42:58.540: e/androidruntime(1281): @ android.app.activitythread.access$800(activitythread.java:135) 05-19 03:42:58.540: e/androidruntime(1281): @ android.app.activitythread$h.handlemessage(activitythread.java:1196) 05-19 03:42:58.540: e/androidruntime(1281): @ android.os.handler.dispatchmessage(handler.java:102) 05-19 03:42:58.540: e/androidruntime(1281): @ android.os.looper.loop(looper.java:136) 05-19 03:42:58.540: e/androidruntime(1281): @ android.app.activitythread.main(activitythread.java:5017) 05-19 03:42:58.540: e/androidruntime(1281): @ java.lang.reflect.method.invokenative(native method) 05-19 03:42:58.540: e/androidruntime(1281): @ java.lang.reflect.method.invoke(method.java:515) 05-19 03:42:58.540: e/androidruntime(1281): @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:779) 05-19 03:42:58.540: e/androidruntime(1281): @ com.android.internal.os.zygoteinit.main(zygoteinit.java:595) 05-19 03:42:58.540: e/androidruntime(1281): @ dalvik.system.nativestart.main(native method) 05-19 03:42:58.540: e/androidruntime(1281): caused by: java.lang.nullpointerexception 05-19 03:42:58.540: e/androidruntime(1281): @ com.iitb.practice.mainactivity.oncreate(mainactivity.java:39) 05-19 03:42:58.540: e/androidruntime(1281): @ android.app.activity.performcreate(activity.java:5231) 05-19 03:42:58.540: e/androidruntime(1281): @ android.app.instrumentation.callactivityoncreate(instrumentation.java:1087) 05-19 03:42:58.540: e/androidruntime(1281): @ android.app.activitythread.performlaunchactivity(activitythread.java:2159) 05-19 03:42:58.540: e/androidruntime(1281): ... 11 more 05-19 03:47:59.190: i/process(1281): sending signal. pid: 1281 sig: 9

you need first call "setcontentview()" inside oncreate() before initialize variables.

protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);     addone=(button)findviewbyid(r.id.badd);     subone= (button) findviewbyid(r.id.bsub);     display =(textview) findviewbyid(r.id.tv1);