java - Eclipse: "Unfortunately, XXX has stopped" error when testing on an Android phone -

please forgive me, since first time make android program.

so i've followed tutorial on youtube make simple program take user inputted number, multiply 5 , display on label.

it got no errors. when tried run on android phone, got error "unfortunately, xxx has stopped". i've checked , run hello world program eclipse initiated program with.

thank kind attention.

mainactivity.java

package com.example.converter;  import android.support.v7.app.actionbaractivity; import android.support.v7.app.actionbar; import android.support.v4.app.fragment; import android.os.bundle; import android.view.layoutinflater; import android.view.menu; import android.view.menuitem; import android.view.view; import android.view.viewgroup; import android.widget.*; // * wild character, import widgets import android.os.build;  public class mainactivity extends actionbaractivity {      @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_main);          if (savedinstancestate == null) {             getsupportfragmentmanager().begintransaction()                     .add(r.id.container, new placeholderfragment()).commit();         }          button calc = (button)findviewbyid(r.id.btncalculate);         calc.setonclicklistener(new view.onclicklistener() {                 public void onclick(view v) {                     edittext num = (edittext)findviewbyid(r.id.num);                     textview display = (textview)findviewbyid(r.id.display);                     double number = double.parsedouble(num.gettext().tostring());                     number = number * 5;                     display.settext(number + "");                 }         });     }      @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;         }     }  } 

fragment_main.xml

<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.example.converter.mainactivity$placeholderfragment" >      <textview         android:id="@+id/textview1"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_alignparenttop="true"         android:layout_centerhorizontal="true"         android:layout_margintop="51dp"         android:text="@string/basic_calc"         android:textappearance="?android:attr/textappearancelarge" />      <edittext         android:id="@+id/num"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_below="@+id/textview1"         android:layout_centerhorizontal="true"         android:ems="10"         android:inputtype="numbersigned|numberdecimal" >          <requestfocus />     </edittext>      <button         android:id="@+id/btncalculate"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_below="@+id/num"         android:layout_centerhorizontal="true"         android:layout_margintop="18dp"         android:text="@string/calculate" />      <textview         android:id="@+id/display"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_alignleft="@+id/num"         android:layout_below="@+id/btncalculate"         android:layout_margintop="60dp"         android:textappearance="?android:attr/textappearancelarge" />  </relativelayout> 

androidmanifest.xml

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android"     package="com.example.converter"     android:versioncode="1"     android:versionname="1.0" >      <uses-sdk         android:minsdkversion="8"         android:targetsdkversion="19" />      <application         android:allowbackup="true"         android:icon="@drawable/ic_launcher"         android:label="@string/app_name"         android:theme="@style/apptheme" >         <activity             android:name="com.example.converter.mainactivity"             android:label="@string/app_name" >             <intent-filter>                 <action android:name="android.intent.action.main" />                  <category android:name="android.intent.category.launcher" />             </intent-filter>         </activity>     </application>  </manifest> 

logcat:

03-24 22:34:24.665: e/trace(18634): error opening trace file: no such file or directory (2) 03-24 22:34:24.845: w/dalvikvm(18634): threadid=1: thread exiting uncaught exception (group=0x413b3390) 03-24 22:34:24.865: e/androidruntime(18634): fatal exception: main 03-24 22:34:24.865: e/androidruntime(18634): java.lang.runtimeexception: unable start activity componentinfo{com.example.converter/com.example.converter.mainactivity}: java.lang.nullpointerexception 03-24 22:34:24.865: e/androidruntime(18634):     @ android.app.activitythread.performlaunchactivity(activitythread.java:2355) 03-24 22:34:24.865: e/androidruntime(18634):     @ android.app.activitythread.handlelaunchactivity(activitythread.java:2391) 03-24 22:34:24.865: e/androidruntime(18634):     @ android.app.activitythread.access$600(activitythread.java:151) 03-24 22:34:24.865: e/androidruntime(18634):     @ android.app.activitythread$h.handlemessage(activitythread.java:1335) 03-24 22:34:24.865: e/androidruntime(18634):     @ android.os.handler.dispatchmessage(handler.java:99) 03-24 22:34:24.865: e/androidruntime(18634):     @ android.os.looper.loop(looper.java:155) 03-24 22:34:24.865: e/androidruntime(18634):     @ android.app.activitythread.main(activitythread.java:5511) 03-24 22:34:24.865: e/androidruntime(18634):     @ java.lang.reflect.method.invokenative(native method) 03-24 22:34:24.865: e/androidruntime(18634):     @ java.lang.reflect.method.invoke(method.java:511) 03-24 22:34:24.865: e/androidruntime(18634):     @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:1029) 03-24 22:34:24.865: e/androidruntime(18634):     @ com.android.internal.os.zygoteinit.main(zygoteinit.java:796) 03-24 22:34:24.865: e/androidruntime(18634):     @ dalvik.system.nativestart.main(native method) 03-24 22:34:24.865: e/androidruntime(18634): caused by: java.lang.nullpointerexception 03-24 22:34:24.865: e/androidruntime(18634):     @ com.example.converter.mainactivity.oncreate(mainactivity.java:28) 03-24 22:34:24.865: e/androidruntime(18634):     @ android.app.activity.performcreate(activity.java:5066) 03-24 22:34:24.865: e/androidruntime(18634):     @ android.app.instrumentation.callactivityoncreate(instrumentation.java:1101) 03-24 22:34:24.865: e/androidruntime(18634):     @ android.app.activitythread.performlaunchactivity(activitythread.java:2311) 03-24 22:34:24.865: e/androidruntime(18634):     ... 11 more 03-24 22:34:26.517: d/process(18634): killprocess, pid=18634 03-24 22:34:26.527: d/process(18634): dalvik.system.vmstack.getthreadstacktrace(native method) 03-24 22:34:26.527: d/process(18634): java.lang.thread.getstacktrace(thread.java:599) 03-24 22:34:26.527: d/process(18634): android.os.process.killprocess(process.java:951) 03-24 22:34:26.527: d/process(18634): com.android.internal.os.runtimeinit$uncaughthandler.uncaughtexception(runtimeinit.java:108) 03-24 22:34:26.527: d/process(18634): java.lang.threadgroup.uncaughtexception(threadgroup.java:693) 03-24 22:34:26.527: d/process(18634): java.lang.threadgroup.uncaughtexception(threadgroup.java:690) 03-24 22:34:26.527: d/process(18634): dalvik.system.nativestart.main(native method) 

as eltabo's answer indicates: calc null, because r.id.btncalculate has been declared in fragment_main.xml, you're trying find in mainactivity loads layout activity_main.xml.

so solution move fragment so:

@override public view oncreateview(layoutinflater inflater, viewgroup container, bundle savedinstancestate) {     view view = inflater.inflate(r.layout.fragment_main, container, false);     button calc = (button) view.findviewbyid(r.id.btncalculate);     final edittext num = (edittext) view.findviewbyid(r.id.num);     final textview display = (textview) view.findviewbyid(r.id.display);     calc.setonclicklistener(new view.onclicklistener() {         public void onclick(view v) {             double number = double.parsedouble(num.gettext().tostring());             number = number * 5;             display.settext(number + "");         }     });      return view; }