Apps A trouble on HelloTabWidget

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<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="HelloTabWidget.my"
android:versionCode="1"
android:versionName="1.0">
<application android:icon="@drawable/icon" android:label="@string/app_name">

<activity android:name=".HelloTabWidget"
android:label="@string/app_name"
android:theme="@android:style/Theme.NoTitleBar">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category
android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".ArtistsActivity"
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>
<uses-sdk android:minSdkVersion="8" />
</manifest>


this is an example from the sdk of android ,should the manifest.xml be written like this ? but there is an error :Class
HelloTabWidget.my.ArtistsActivity does not exist.
I'm confused by it .can anyone help me?