Error type 3 Activity class does not exist

import java.util.Comparator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.SortedSet;
import java.util.TreeMap;
import java.util.TreeSet;

public class MainClass {
	public static void main(String[] arg) {

		// english;germany dictionary
		String[] arrayOfString = { "one;eine", "two;zwei", "three;drei",
				"four;vier" };

		Map<String, String> map = new TreeMap<String, String>();

		for (String s : arrayOfString) {
			String[] array = s.split(";");
			String sKey = "", sValue = "";
			if (array.length > 1) {
				sKey = array[0];
				sValue = array[1];
				map.put(sKey, sValue);
			}
		}
		for (Entry<String, String> entry: mapSortedByValues(map)) {
		    System.out.println(entry.getKey() + " = " + entry.getValue());
		}
	}

	static <K, V extends Comparable<? super V>> SortedSet<Map.Entry<K, V>> mapSortedByValues(
			Map<K, V> map) {
		SortedSet<Map.Entry<K, V>> sortedSetOfEntries = new TreeSet<Map.Entry<K, V>>(
				new Comparator<Map.Entry<K, V>>() {
					@Override
					public int compare(Map.Entry<K, V> entry_1, Map.Entry<K, V> entry_2) {
						int res = entry_1.getValue().compareTo(entry_2.getValue());
						return res != 0 ? res : 1; 
						// return entry_1.getValue().compareTo(entry_2.getValue());							
					}
				});
		sortedSetOfEntries.addAll(map.entrySet());
		return sortedSetOfEntries;
	}
}
/*
three = drei
one = eine
four = vier
two = zwei
 */

       <activity
 android:name=".Tests_Activity"
 android:label="@string/app_name"
 android:configChanges="keyboard|keyboardHidden|orientation|screenLayout|uiMode|screenSize|smallestScreenSize" />

// in AndroidManifest.xml
<Activity
 android:screenOrientation="portrait" // or landscape

// in MyActivity.java
boolean mbOrientacionLandscape = false;
int nOrientation =	getResources().getConfiguration().orientation;
if(mbOrientacionLandscape==true){
	 getResources().getConfiguration();
	if(nOrientation != Configuration.ORIENTATION_LANDSCAPE)
	setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
	
}
else{
	if(nOrientation != Configuration.ORIENTATION_PORTRAIT)
	setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
}

int mCurrentPhotoIndex = 0;
   @Override
    protected void onSaveInstanceState(Bundle outState) {
        outState.putInt("photo_index", mCurrentPhotoIndex);
        super.onSaveInstanceState(outState);
    }

    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        mCurrentPhotoIndex = savedInstanceState.getInt("photo_index");
        super.onRestoreInstanceState(savedInstanceState);
    }

// or save preferences for new start of Activity in onStop
//onCreate or onResume or onStart etc.
public void loadPreferences() {
		SharedPreferences settings = getSharedPreferences(F.PREFERENCES_NAME, 0);
		mCurrentPhotoIndex = settings.getInt("mCurrentPhotoIndex",mCurrentPhotoIndex);
	// String_sOtazka = settings.getString("_sOtazka", _sOtazka);


}
// onStop
public void savePreferences() {
		SharedPreferences settings = getSharedPreferences(PREFERENCES_NAME, 0);
		SharedPreferences.Editor editor = settings.edit();
		editor.putInt("mCurrentPhotoIndex", mCurrentPhotoIndex);
                // String, boolean, float ...
		// editor.putString("mButton1", mButton1.getText().toString());

		editor.commit();

}