android - Sudoku crashes when 'about' button is clicked -

hi new android , have been trying simple sudoku application. facing problem now,whenever click "about" button applocation tends stop , takes me menu screen. can suggest problem crash??

below here code:

sudoku.java

public class sudoku extends activity implements onclicklistener {  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_sudoku);     view continuebutton=findviewbyid(r.id.button1);     continuebutton.setonclicklistener(this);     view newbutton=findviewbyid(r.id.button2);     newbutton.setonclicklistener(this);     view aboutbutton=findviewbyid(r.id.button3);     aboutbutton.setonclicklistener(this);     view exitbutton=findviewbyid(r.id.button4);     exitbutton.setonclicklistener(this); }          public void onclick(view v){         switch(v.getid()){         case r.id.button3:             intent = new intent(this, about.class);             startactivity(i);             break;         case r.id.button4:             finish();             break;              }           }         @override            public boolean oncreateoptionsmenu(menu menu) {               super.oncreateoptionsmenu(menu);               menuinflater inflater = getmenuinflater();               inflater.inflate(r.menu.menu, menu);               return true;            }   } 

about.java

public class extends activity { @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.about); } } 

about.xml:

public class extends activity { @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.about); } } 

string.xml:

<?xml version="1.0" encoding="utf-8"?> 

<string name="app_name">sudoku</string> <string name="action_settings">settings</string> <string name="hello_world">application sudoku</string> <string name="continue_label">continue</string> <string name="new_game_label">new game</string> <string name="about_label">about</string> <string name="exit_label">exit</string> <string name="about_title">about android sudoku</string> <string name="about_text">\sudoku logic-based number placement puzzle. 

starting partially completed 9x9 grid, objective fill grid each row, each column, , each of 3x3 boxes (also called blocks) contains digits 1 9 once..

activity_sudoku.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" android:background="@color/background" tools:context=".sudoku" >  <textview     android:id="@+id/textview1"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:text="@string/hello_world"     android:textstyle="italic" />  <tablelayout      android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:layout_gravity="center"     android:stretchcolumns="*">     <tablerow >  <button     android:id="@+id/button1"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:layout_alignleft="@+id/textview1"     android:layout_below="@+id/textview1"     android:layout_margintop="22dp"     android:text="@string/continue_label"     android:textstyle="italic"      />  <button     android:id="@+id/button2"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:layout_alignleft="@+id/button1"     android:layout_below="@+id/button1"     android:layout_margintop="21dp"     android:text="@string/new_game_label"      android:textstyle="italic"     />   </tablerow> <tablerow >      <button         android:id="@+id/button3"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_margintop="16dp"         android:text="@string/about_label"          />      <button         android:id="@+id/button4"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_margintop="16dp"         android:text="@string/exit_label"          />  </tablerow> </tablelayout>  </relativelayout> 

sudoku manifest.xml:

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="org.example.sudoku" android:versioncode="1" android:versionname="1.0" >  <uses-sdk     android:minsdkversion="8"     android:targetsdkversion="17" />  <application     android:allowbackup="true"     android:icon="@drawable/ic_launcher"     android:label="@string/app_name"     android:theme="@style/apptheme" >     <activity         android:name="org.example.sudoku.sudoku"         android:label="@string/app_name" >         <intent-filter>             <action android:name="android.intent.action.main" />              <category android:name="android.intent.category.launcher" />         </intent-filter>     </activity>     <activity         android:name="org.example.sudoku.about"         android:label="@string/about_title"         android:theme="@android:style/theme.dialog">     </activity> </application>  </manifest> 

you should try adding intent-filter manifest.xml. faced problem lot during starting android prog. add such as:

<activity     android:name="org.example.sudoku.sudoku"     android:label="@string/app_name" >     <intent-filter>         <action android:name="android.intent.action.main" />          <category android:name="android.intent.category.launcher" />     </intent-filter> </activity> <activity     android:name="org.example.sudoku.about"     android:label="@string/about_title"     android:theme="@android:style/theme.dialog">     <intent-filter>         <action android:name="org.example.sudoku.about" />         <category android:name="android.intent.category.default" />     </intent-filter> </activity> 

later in sudoku.java update part:

case r.id.button3:         intent = new intent(this, about.class);         startactivity(i);         break; 

update above as:

case r.id.button3:         startactivity(new intent("org.example.sudoku.about"));         break; 

this should solve problem.