java - how to create an activity nested to an other activity -

i'm trying create mapdisplay activity mainactivity have error.

androidmanifest

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.example.fin2" android:versioncode="1" android:versionname="1.0" >     <uses-sdk     android:minsdkversion="12"     android:targetsdkversion="18" />     <permission      android:name="com.example.fin2.permission.maps_receive"     android:protectionlevel="signature"     />     <uses-permission android:name="com.example.fin2.permission.maps_receive"/>     <uses-permission android:name="android.permission.internet"/> <uses-permission android:name="android.permission.access_network_state"/> <uses-permission android:name="android.permission.write_external_storage"/> <uses-permission     android:name="com.google.android.providers.gsf.permission.read_gservices"/> <!-- following 2 permissions not required use      google maps android api v2, recommended. --> <uses-permission android:name="android.permission.access_coarse_location"/> <uses-permission android:name="android.permission.access_fine_location"/>   <uses-feature     android:glesversion="0x00020000"     android:required="true"/>        <application     android:allowbackup="true"     android:icon="@drawable/ic_launcher"     android:label="@string/app_name"     android:theme="@style/apptheme" >         <meta-data             android:name="com.google.android.maps.v2.api_key"             android:value="aizasybubw3lo3wuzhkldrreutma1xml5gbmaim"/>         <activity         android:name="com.example.fin2.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>          <activity          android:name=".map_display_activity"               />     </application>     </manifest> 

and source code

package com.example.fin2;    import android.os.bundle; import android.app.activity; import android.content.intent; import android.view.menu; import android.view.menuinflater; import android.view.menuitem; import android.widget.toast;  public class mainactivity extends activity {  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.main); }          @override         public boolean oncreateoptionsmenu(menu menu) {     // inflate menu; adds items action bar if present.     menuinflater inflater = getmenuinflater();     inflater.inflate(r.menu.main, menu);      return true; }      @override     public boolean onoptionsitemselected(menuitem item) {     // todo auto-generated method stub      switch (item.getitemid()) {      case r.id.display_map :          intent intent = new intent(mainactivity.this,      map_display_activity.class);         startactivity(intent);          return true;      case r.id.autres :         return true;      case r.id.quitter:         finish();         return true;       }     return false; }     public class map_display_activity extends activity {      @override     protected void oncreate(bundle savedinstancestate) {         // todo auto-generated method stub         super.oncreate(savedinstancestate);          setcontentview(r.layout.map_display);          intent intent = getintent();          if (intent != null) {             toast.maketext(map_display_activity.this, "diplay map", toast.length_short).show();          }     }  }  } 

error code:

android.content.activitynotfoundexception: unable find explicit activity class {com.example.fin2/com.example.fin2.mainactivity$map_display_activity}; have declared activity in androidmanifest.xml?