Error type 3 Activity class does not exist

 <application
        android:allowBackup="true"
        android:icon="@drawable/dicts_ico"
        android:label="@string/app_name" 
        android:theme="@style/AppTheme" // delete this row - run app - try menu
 >

<resources>

    <!--
        Base application theme, dependent on API level. This theme is replaced
        by AppBaseTheme from res/values-vXX/styles.xml on newer devices.
    -->
    <style name="AppBaseTheme" parent="android:Theme.Black">
        <!--
            Theme customizations available in newer API levels can go in
            res/values-vXX/styles.xml, while customizations related to
            backward-compatibility can go here.
        -->
    </style>

    <!-- Application theme. -->
    <style name="AppTheme" parent="AppBaseTheme">
        <!-- All customizations that are NOT specific to a particular API-level can go here. -->
    </style>

</resources>

        int[] mArrayOfInt;
        String[] mArrayOfString;
        List<String> mList;
        public void saveState(Bundle map)
        {
                map.putIntArray("mArrayOfInt", mArrayOfInt);
                map.putStringArray("mArrayOfString", mArrayOfString);
                map.putStringArrayList("mList", mList);
        }

        public void restoreState(Bundle map)
        {
                mArrayOfInt= map.getIntArray("mArrayOfInt");
                mArrayOfString = map.getStringArray("mArrayOfString");
                mList = map.getStringArrayList("mList");

        }

public class MainClass {
	public static void main(String[] arg) {
		String[] arrayOfString = { "Hello", "people", "hello", "world!" };

		for (int i = 0; // start position , first cycle i == 0
                      i < arrayOfString.length; // if i < 4 (length of array) do loop
                       i++ // incrementation after cycle
                       ){
			System.out.println(arrayOfString[i]); 
                       // i++ incrementation
		}
	}
}

      Intent i = new Intent(this, MyNextClass.class);
      startActivity(i);

 public void createDatabase(Context myContext) throws IOException {
    String sPackName = myContext.getPackageName();
    InputStream assetsDB = myContext.getAssets().open("myDatabase");
    OutputStream dbOut = new FileOutputStream("/data/data/"+sPackName+"/database");
 
    byte[] buffer = new byte[1024];
    int length;
    while ((length = assetsDB.read(buffer))>0){
      dbOut.write(buffer, 0, length);
    }
 
    dbOut.flush();
    dbOut.close();
    assetsDB.close();
}