java - Android application has stopped working -eclipse -

i have been tried build first android application. every time open application in emulator, message says test has stopped working. must simple. hope can me.

04-06 15:43:47.806: w/dalvikvm(4275): threadid=1: thread exiting uncaught exception (group=0xa614d908)

04-06 15:43:47.826: e/androidruntime(4275): fatal exception: main

04-06 15:43:47.826: e/androidruntime(4275): java.lang.runtimeexception: unable start activity componentinfo{com.test/com.test.mainactivity}: java.lang.nullpointerexception

04-06 15:43:47.826: e/androidruntime(4275): @ android.app.activitythread.performlaunchactivity(activitythread.java:2180)

04-06 15:43:47.826: e/androidruntime(4275): @ android.app.activitythread.handlelaunchactivity(activitythread.java:2230)

04-06 15:43:47.826: e/androidruntime(4275): @ android.app.activitythread.access$600(activitythread.java:141)

04-06 15:43:47.826: e/androidruntime(4275): @ android.app.activitythread$h.handlemessage(activitythread.java:1234)

04-06 15:43:47.826: e/androidruntime(4275): @ android.os.handler.dispatchmessage(handler.java:99)

04-06 15:43:47.826: e/androidruntime(4275): @ android.os.looper.loop(looper.java:137)

04-06 15:43:47.826: e/androidruntime(4275): @ android.app.activitythread.main(activitythread.java:5041)

04-06 15:43:47.826: e/androidruntime(4275): @ java.lang.reflect.method.invokenative(native method)

04-06 15:43:47.826: e/androidruntime(4275): @ java.lang.reflect.method.invoke(method.java:511)

04-06 15:43:47.826: e/androidruntime(4275): @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:793)

04-06 15:43:47.826: e/androidruntime(4275): @ com.android.internal.os.zygoteinit.main(zygoteinit.java:560)

04-06 15:43:47.826: e/androidruntime(4275): @ dalvik.system.nativestart.main(native method)

04-06 15:43:47.826: e/androidruntime(4275): caused by: java.lang.nullpointerexception

04-06 15:43:47.826: e/androidruntime(4275): @ com.test.mainactivity.oncreate(mainactivity.java:30)

04-06 15:43:47.826: e/androidruntime(4275): @ android.app.activity.performcreate(activity.java:5104)

04-06 15:43:47.826: e/androidruntime(4275): @ android.app.instrumentation.callactivityoncreate(instrumentation.java:1080)

04-06 15:43:47.826: e/androidruntime(4275): @ android.app.activitythread.performlaunchactivity(activitythread.java:2144)

04-06 15:43:47.826: e/androidruntime(4275): ... 11 more

above log file

public class main extends actionbaractivity {      int counter ;         button add, sub ;         textview display;      @override     protected void oncreate(bundle savedinstancestate) {           super.oncreate(savedinstancestate);       setcontentview(r.layout.activity_main);       counter = 0;           add = (button) findviewbyid (r.id.badd);           sub = (button) findviewbyid (r.id.bsub);           display = (textview) findviewbyid(r.id.tvdisplay);           add.setonclicklistener(new  view.onclicklistener() {              @override             public void onclick(view v) {                 // todo auto-generated method stub                 counter++;                 display.settext("your total " + counter);              }         });            sub.setonclicklistener(new  view.onclicklistener() {              @override             public void onclick(view v) {                 // todo auto-generated method stub                 counter --;                 display.settext("your total " + counter);             }         });           if (savedinstancestate == null) {             getsupportfragmentmanager().begintransaction()                .add(r.id.container, new placeholderfragment()).commit();         }     }          @override     public boolean oncreateoptionsmenu(menu menu) {          // inflate menu; adds items action bar if present.         getmenuinflater().inflate(r.menu.main, menu);         return true;     }         @override     public boolean onoptionsitemselected(menuitem item) {         // handle action bar item clicks here. action bar         // automatically handle clicks on home/up button, long         // specify parent activity in androidmanifest.xml.         int id = item.getitemid();         if (id == r.id.action_settings) {             return true;         }         return super.onoptionsitemselected(item);     }  /**      * placeholder fragment containing simple view.      */     public static class placeholderfragment extends fragment {          public placeholderfragment() {         }          @override         public view oncreateview(layoutinflater inflater, viewgroup container,bundle savedinstancestate) {             view rootview = inflater.inflate(r.layout.fragment_main, container,                     false);             return rootview;         }     }  } 

above main class

<relativelayout xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:tools="http://schemas.android.com/tools"     android:layout_width="match_parent"     android:layout_height="match_parent"     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.test.mainactivity$placeholderfragment" >     <textview         android:id="@+id/tvdisplay"         android:layout_width="wrap_content"         android:layout_height="match_parent"         android:layout_alignleft="@+id/bsub"         android:layout_alignparentbottom="true"         android:layout_below="@+id/bsub"         android:gravity="center"         android:text="your total 0"         android:textsize="45dp" />      <button         android:id="@+id/badd"         android:layout_width="250dp"         android:layout_height="wrap_content"         android:layout_alignparentleft="true"         android:layout_alignparenttop="true"         android:layout_marginleft="16dp"         android:layout_margintop="78dp"         android:gravity="center"         android:text="add one"         android:textsize="20dp" />      <button         android:id="@+id/bsub"         android:layout_width="250dp"         android:layout_height="wrap_content"         android:layout_torightof="@+id/badd"         android:layout_centerhorizontal="true"         android:gravity="center"         android:text="subtract one"         android:textsize="20dp" />    </relativelayout> 

above fragment_main.xml

<framelayout xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:tools="http://schemas.android.com/tools"     android:id="@+id/container"     android:layout_width="match_parent"     android:layout_height="match_parent"     tools:context="com.hello.firstapp.main"     tools:ignore="mergerootframe" /> 

above activity_main.xml

instead of oncreate() move ur initialization oncreateview() buttons , textview in ur fragment_main.xml thats why u got npe buttons , textview not part of activity_main.xml.

@override public view oncreateview(layoutinflater inflater, viewgroup container,bundle savedinstancestate) {             view rootview = inflater.inflate(r.layout.fragment_main, container, false); counter = 0; add = (button) rootview.findviewbyid (r.id.badd); sub = (button) rootview.findviewbyid (r.id.bsub); display = (textview) rootview.findviewbyid(r.id.tvdisplay); add.setonclicklistener(new  view.onclicklistener() {   @override  public void onclick(view v) {  // todo auto-generated method stub   counter++;    display.settext("your total " + counter);      }    });    sub.setonclicklistener(new  view.onclicklistener() {     @override    public void onclick(view v) {    // todo auto-generated method stub    counter --;    display.settext("your total " + counter);    }   });  return rootview; }