Need to clear the list of contacts in my android app. Please help)

I'm writting my own android app for storing contacts (name, phone number, email). I've got a database, two activity, one for displaying the list of contacts and the other for filling a form with a contact data. The probleme is that I don't know how to delete all conctacts from the list and also how to delete a single contact from the list. I will show you my code.

    package com.example.contactsapp;

public class Contact {



    //private variables
    int _id;
    String _name;
    String _lastName;
    String _phone_number;
    String _email;

    // Empty constructor
    public Contact(){

    }
    // constructor
    public Contact(int id, String name, String lastName, String _phone_number, String email){
        this._id = id;
        this._name = name;
        this._lastName = lastName;
        this._phone_number = _phone_number;
        this._email = email;
    }

    // constructor
    public Contact(String name, String lastName, String _phone_number, String email){
        this._name = name;
        this._lastName = lastName;
        this._phone_number = _phone_number;
        this._email = email;
    }
    // getting ID
    public int getID(){
        return this._id;
    }

    // setting id
    public void setID(int id){
        this._id = id;
    }

    // getting name
    public String getName(){
        return this._name;
    }

    // setting name
    public void setName(String name){
        this._name = name;
    }

    // getting lastName
    public String getLastName(){
        return this._lastName;
    }

 // setting lastName
    public void setLastName(String lastName){
        this._lastName = lastName;
    }

    // getting phone number
    public String getPhoneNumber(){
        return this._phone_number;
    }

    // setting phone number
    public void setPhoneNumber(String phone_number){
        this._phone_number = phone_number;
    }

 // getting lastName
    public String getEmail(){
        return this._email;
    }

 // setting lastName
    public void setEmail(String email){
        this._email = email;
    }
}

    package com.example.contactsapp;

import java.util.ArrayList;
import java.util.List;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DatabaseHandler extends SQLiteOpenHelper {

    // All Static variables
    // Database Version
    private static final int DATABASE_VERSION = 1;

    // Database Name
    private static final String DATABASE_NAME = "contactsManager";

    // Contacts table name
    private static final String TABLE_CONTACTS = "contacts";

    // Contacts Table Columns names
    private static final String KEY_ID = "id";
    private static final String KEY_NAME = "name";
    private static final String KEY_LAST_NAME = "last_name";
    private static final String KEY_PH_NO = "phone_number";
    private static final String KEY_EMAIL = "email";

    public DatabaseHandler(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    // Creating Tables
    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CONTACTS + "("
                + KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT," + KEY_LAST_NAME + " TEXT,"
                + KEY_PH_NO + " TEXT," + KEY_EMAIL + " TEXT" + ")";
        db.execSQL(CREATE_CONTACTS_TABLE);
    }

    // Upgrading database
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // Drop older table if existed
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS);

        // Create tables again
        onCreate(db);
    }

    /**
     * All CRUD(Create, Read, Update, Delete) Operations
     */

    // Adding new contact
    public void addContact(Contact contact) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_NAME, contact.getName()); // Contact Name
        values.put(KEY_LAST_NAME, contact.getLastName()); // Contact Last Name
        values.put(KEY_PH_NO, contact.getPhoneNumber()); // Contact Phone
        values.put(KEY_EMAIL, contact.getEmail()); // Contact Email

        // Inserting Row
        db.insert(TABLE_CONTACTS, null, values);
        db.close(); // Closing database connection
    }

    // Getting single contact
    Contact getContact(int id) {
        SQLiteDatabase db = this.getReadableDatabase();

        Cursor cursor = db.query(TABLE_CONTACTS, new String[] { KEY_ID,
                KEY_NAME, KEY_LAST_NAME, KEY_PH_NO, KEY_EMAIL }, KEY_ID + "=?",
                new String[] { String.valueOf(id) }, null, null, null, null);
        if (cursor != null)
            cursor.moveToFirst();

        Contact contact = new Contact(Integer.parseInt(cursor.getString(0)),
                cursor.getString(1), cursor.getString(2), cursor.getString(3), cursor.getString(4));
        // return contact
        return contact;
    }

    // Getting All Contacts
    public List<Contact> getAllContacts() {
        List<Contact> contactList = new ArrayList<Contact>();
        // Select All Query
        String selectQuery = "SELECT  * FROM " + TABLE_CONTACTS;

        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(selectQuery, null);

        // looping through all rows and adding to list
        if (cursor.moveToFirst()) {
            do {
                Contact contact = new Contact();
                contact.setID(Integer.parseInt(cursor.getString(0)));
                contact.setName(cursor.getString(1));
                contact.setLastName(cursor.getString(2));
                contact.setPhoneNumber(cursor.getString(3));
                contact.setEmail(cursor.getString(4));

                String name = cursor.getString(1) +"\n"+ cursor.getString(2) +"\n"+ cursor.getString(3) +"\n"+ cursor.getString(4);
                MainActivity.ArrayofName.add(name);
                // Adding contact to list
                contactList.add(contact);
            } while (cursor.moveToNext());
        }

        // return contact list
        return contactList;
    }

    // Updating single contact
    public int updateContact(Contact contact) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_NAME, contact.getName());
        values.put(KEY_LAST_NAME, contact.getLastName());
        values.put(KEY_PH_NO, contact.getPhoneNumber());
        values.put(KEY_EMAIL, contact.getEmail());

        // updating row
        return db.update(TABLE_CONTACTS, values, KEY_ID + " = ?",
                new String[] { String.valueOf(contact.getID()) });
    }

    //public void clearDataBase(SQLiteDatabase db) {
        //db.execSQL("DROP TABLE " + TABLE_CONTACTS);
        //onCreate(db);
    //}

    // Deleting single contact
    public void deleteContact(Contact contact) {
        SQLiteDatabase db = this.getWritableDatabase();
        db.delete(TABLE_CONTACTS, KEY_ID + " = ?",
                new String[] { String.valueOf(contact.getID()) });
        db.close();
    }


    // Getting contacts Count
    public int getContactsCount() {
        String countQuery = "SELECT  * FROM " + TABLE_CONTACTS;
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.rawQuery(countQuery, null);
        cursor.close();

        // return count
        return cursor.getCount();
    }

}

public class MainActivity extends Activity {

    DatabaseHandler db = new DatabaseHandler(this);

    private ListView listView;
    public static ArrayList<String> ArrayofName = new ArrayList<String>();

    //For menu
    private Menu m = null;

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        super.onCreateOptionsMenu(menu);
        MenuInflater inflater = getMenuInflater();
        //R.menu.menu est l'id de notre menu
        inflater.inflate(R.menu.menu, menu);
        m = menu;
        return true;
    }


    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

       db.getAllContacts();

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

        registerForContextMenu(listView);
        listView.setOnCreateContextMenuListener(this);

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
                android.R.layout.simple_list_item_1, ArrayofName);

        listView.setAdapter(adapter);

        listView.setOnItemClickListener(new OnItemClickListener() {
            public void onItemClick(AdapterView<?> parent, View v,
                int position, long id) {
               Toast.makeText(getApplicationContext(),
                ((TextView) v).getText(), Toast.LENGTH_SHORT).show();
               //db.deleteContact();
            }
        });
    }

    public void onCreateContextMenu(ContextMenu menu, View v,
            ContextMenuInfo menuInfo) {
        super.onCreateContextMenu(menu, v, menuInfo);
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.menu, menu);
    }

    //For menu
    @Override
    public boolean onOptionsItemSelected (MenuItem item)
    {

        final Context context = this;

      switch(item.getItemId())
      {
        case R.id.item1:
          //Dans le Menu "m", on active tous les items dans le groupe d'identifiant "R.id.group2"
          //m.setGroupEnabled(R.id.group2, true);
          //return true;
            Intent intent = new Intent(context, Form.class);
            startActivity(intent);
            //break;
        //case R.id.item2:
            //db.clearDataBase(db);
            //break;
      }
      return super.onOptionsItemSelected(item);
    }
}

In the MainActivity, when I call the menu, there are two options. The second one is supposed to delete all conctacts from the list. My friends, I don't how to implement it, please help

Thanks a lot in advance, Karen.