how can i call the updateContact method from DataBaseHandler.java in MainActivity

public class DataBaseHandler extends SQLiteOpenHelper {

// Version de la BD
private static final int DATA_BASE_VERSION = 1;
// Nom de la BD
private static final String DATA_BASE_NAME = "contactsManager";
// Nom de la table Contacts
private static final String TABLE_CONTACTS = "contacts";
// Colonnes de la table Contacts
private static final String KEY_ID = "id";
static final String KEY_NAME = "name";
static final String KEY_PH_NB = "phone_number";
private SQLiteDatabase maBaseDeDonnees;
private DataBaseHandler baseHandler;
// méthode permettant d'ouvrir la base en écriture
public void open() {
    maBaseDeDonnees = baseHandler.getWritableDatabase();
}
public DataBaseHandler(Context context, String name, SQLiteDatabase.CursorFactory factory,
                       int version) {
    super(context, DATA_BASE_NAME, null, DATA_BASE_VERSION);
}
@Override

public void onCreate(SQLiteDatabase db) {
    String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CONTACTS + "("
            + KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT,"
            + KEY_PH_NB + " TEXT" + ")";
    db.execSQL(CREATE_CONTACTS_TABLE);
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS);

    onCreate(db);
}


void addContact(Contact contact) {
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues values = new ContentValues();
    values.put(KEY_NAME, contact.getName()); // Nom du contact
    values.put(KEY_PH_NB, contact.getPhone_number()); // Tel du contact

    db.insert(TABLE_CONTACTS, null, values);
    db.close(); // Fermer la connection à la base de données
}

Contact getContact(int id) {
    SQLiteDatabase db = this.getReadableDatabase();

    Cursor cursor = db.query(TABLE_CONTACTS, new String[] { KEY_ID,
                    KEY_NAME, KEY_PH_NB }, KEY_ID + "=?",
            new String[] { String.valueOf(id) }, null, null, null, null);
    if (cursor != null) // il existe un contact avec l'id spécifié
        cursor.moveToFirst();

    Contact contact = new Contact(Integer.parseInt(cursor.getString(0)),
            cursor.getString(1), cursor.getString(2));

    db.close();
    return contact;
}

public List<Contact> getAllContacts() {
    List<Contact> contactList = new ArrayList<Contact>();

    String selectQuery = "SELECT * FROM " + TABLE_CONTACTS;
    SQLiteDatabase db = this.getWritableDatabase();
    Cursor cursor = db.rawQuery(selectQuery, null);

    if (cursor.moveToFirst()) {
        do {
            Contact contact = new Contact();
            contact.setId(Integer.parseInt(cursor.getString(0)));
            contact.setName(cursor.getString(1));
            contact.setPhone_number(cursor.getString(2));

            contactList.add(contact);
        } while (cursor.moveToNext());
    }

    return contactList;
}


public int removeContact(String name) {

    return maBaseDeDonnees.delete(DATA_BASE_NAME, KEY_NAME + "LIKE" + name,
            null);
}

public int updateContact(Contact c) {
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues val = new ContentValues();
    val.put(KEY_NAME, c.getName());
    val.put(KEY_PH_NB, c.getPhone_number());
    return db.update(TABLE_CONTACTS, val, KEY_ID + "=?",
            new String[] { String.valueOf(c.getId()) });
}
public void deleteContact(Contact c) {
    SQLiteDatabase db = this.getWritableDatabase();
    db.delete(TABLE_CONTACTS, KEY_ID + "=?",
            new String[] { String.valueOf(c.getId()) });
    db.close();
}
public int getContactsNumber() {
    String req = "SELECT * FROM " + TABLE_CONTACTS;
    SQLiteDatabase db = this.getWritableDatabase();
    Cursor c = db.rawQuery(req, null);
    c.close();
    return c.getCount();
}

} public class MainActivity extends Activity {

String nom, tel;
// Version de la BD
private static final int DATA_BASE_VERSION = 1;
// Nom de la BD
private static final String DATA_BASE_NAME = "contactsManager";

DataBaseHandler db = new DataBaseHandler(this, DATA_BASE_NAME, null, DATA_BASE_VERSION);


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_add_contact);

    ListView lv = (ListView) findViewById(R.id.listView1);

    String[] values = new String[] { "Afficher tous les contacts",
            "Ajouter un contact",
            "Modifier un contact",};

    ArrayAdapter adapter = new ArrayAdapter<String>(this,R.layout.simplerow,values);

// Associer la listView XML à java //Affichage de tous les contacts

    lv.setAdapter(adapter);
    lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

//hjhgjgjghgv lljklnkjnj if (position==0) {

               EditText edt = (EditText) findViewById(R.id.editText);
               String resultat = String.valueOf(db.getAllContacts());
               edt.setText(String.valueOf(resultat));

           }else if (position==1){

               EditText ed1 = (EditText) findViewById(R.id.editnom);
               EditText ed2 = (EditText) findViewById(R.id.editphone);
               nom = ed1.getText().toString();
               tel = ed2.getText().toString();
               db.getWritableDatabase();
               db.getReadableDatabase();
               Contact nouveauContact = new Contact();
               nouveauContact.setName(nom);
               nouveauContact.setPhone_number(tel);
               Log.d("Reading: ", "Reading all contacts..");
               List<Contact> contacts = db.getAllContacts();
               for (Contact cn : contacts) {
                   String log = "Id: " + cn.getId() + " ,Name: " + cn.getName() + " ,Phone: " + cn.getPhone_number();
                   // Writing Contacts to log
                   Log.d("Name: ", log);
               }
           }
        }
    }); 

}