android database: the method open() is undefined for the type databasehelper class

i want to authenticate user id and password from sqlite database. The user table is saved in sqlite db, i want to compare the edittext value with the value saved in the sqlite db, when i initialize and open the database i get error that the method open() is undefined for the Db_getUserDetail (name of my database helper class).

code of main activity

@Override
public void onClick(View v) {

ffCode = ed_login.getText().toString();
password = ed_password.getText().toString();
// check if any of edit text is empty
     if(ffCode.equals(""))
         {
         Toast.makeText(getApplicationContext(), "Please enter your FF code",    Toast.LENGTH_LONG).show();
               return;
          }

     else if (password.equals(""))
         {
         Toast.makeText(getApplicationContext(), "Please enter your password", Toast.LENGTH_LONG).show();
                return;
          }
              Log.e("opening database", "yes");
              Db_getUserDetail  myDb= new Db_getUserDetail(MainActivity.this);
              myDb.open();
              //this is the method to query
              String storedffcode=Db_getUserDetail.getCodeAndPassword(ffCode);
              myDb.close(); 

              if(ffCode.equals(storedffcode))
                {
                Toast.makeText(getApplicationContext(), "Congrats: Login Successfull", Toast.LENGTH_LONG).show();

                }
                else
                {
                    Toast.makeText(getApplicationContext(), "User Name or Password does not match", Toast.LENGTH_LONG).show();
                }

        }

    });

code for getting values from database

    public static  String getCodeAndPassword(String ffCode)
    {
       Log.e("retrieving ff code", "yes");
       SQLiteDatabase db = null;
       Cursor cursor =   db.query("user_detail", null, " ff_code=?" , new String[]{ffCode}, null, null, null);
       if(cursor.getCount()<1)
        {
            cursor.close();
            return "Not Exist";
        }
        Log.e("found ff code", "yes");
        cursor.moveToFirst();
        String ffcode= cursor.getString(cursor.getColumnIndex("ff_code"));
        return ffcode;
    }

log cat:

java.lang.NullPointerException at com.example.db_client.Db_getUserDetail.getCodeAndPassword(Db_getUserDetail.java:135) at com.example.db_client.UserDetailActivity$1.onClick(UserDetailActivity.java:75) at android.view.View.performClick(View.java:4438) at android.view.View$PerformClick.run(View.java:18422) at android.os.Handler.handleCallback(Handler.java:733) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:136)enter code here

code of db helper class

public class Db_getUserDetail extends SQLiteOpenHelper {

public static final String DATABASE_NAME = "CRM";
public static final String CONTACTS_TABLE_NAME =          "user_detail";
public static final String CONTACTS_COLUMN_USER_ID =      "user_id";
public static final String CONTACTS_COLUMN_USER_PWD =     "user_pwd";
public static final String CONTACTS_COLUMN_FF_CODE=        "ff_code";
public static final String CONTACTS_COLUMN_FF_NAME =       "ff_name";
public static final String CONTACTS_COLUMN_TERR_CODE =     "terr_code";
public static final String CONTACTS_COLUMN_DG_CODE=       "dg_code";
public static final String CONTACTS_COLUMN_DIST_CODE =     "dist_code";
public static final String CONTACTS_COLUMN_FF_MOB =         "ff_mob";
public static final String CONTACTS_COLUMN_IMEI_NO =        "imeino";

  //constructor for database class DBHelper....
    public Db_getUserDetail(Context context)
    {
        super(context, DATABASE_NAME , null, 1);
    }

      String ff_code;   
      String ff_name;
      String terr_code;
      String dg_code;
      String dist_code;
      String  ff_mob;
      String imeino;

    //override onCreate method to create Database table...
    @Override
    public void onCreate(SQLiteDatabase db)
    {
        // TODO Auto-generated method stub.
        Log.e("DB created", "yes");
        db.execSQL("create table user_detail" + "(user_id text, user_pwd text,ff_code text,ff_name text,terr_code text,dg_code text, dist_code text,ff_mob text,imeino text) ");
    }

    //Upgrade new Table...
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // TODO Auto-generated method stub
        db.execSQL("DROP TABLE IF EXISTS user_detail");
        onCreate(db);
    }
    //to insert new records in table...
    public boolean insertUserData (String user_id, String user_pwd, String ff_code ,String ff_name,String terr_code,String dg_code, String dist_code,
                              String ff_mob, String imeino)                                                                                     

    {
        Log.e("DB insert call", "yes");

        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();

        Log.e("content values", "yes");
        contentValues.put("user_id", user_id);
        contentValues.put("user_pwd", user_pwd);    
        contentValues.put("ff_code", ff_code);
        contentValues.put("ff_name",ff_name);   
        contentValues.put("terr_code", terr_code);  
        contentValues.put("dg_code", dg_code);  
        contentValues.put("dist_code", dist_code);  
        contentValues.put("ff_mob", ff_mob);    
        contentValues.put("imeino", imeino);    

        db.insert("user_detail", null, contentValues);
        return true;
    }

    //get data from table...
    public Cursor getData(String id)
    {
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor res =  db.rawQuery( "select * from user_detail", null );
        return res;
    }

    //get no of rows in table...
    public int numberOfRows(){
        SQLiteDatabase db = this.getReadableDatabase();
        int numRows = (int) DatabaseUtils.queryNumEntries(db, CONTACTS_TABLE_NAME);
        return numRows;
    }

    //to delete data from table at particular id....
    public Integer deleteContact (String id)
    {
        SQLiteDatabase db = this.getWritableDatabase();
        return db.delete("user_detail","id = '"+id+"'", null);
    }
    //to get all data from database...
    public ArrayList getAllCotacts() 
    {
        ArrayList array_list = new ArrayList();
        //hp = new HashMap();
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor res =  db.rawQuery( "select * from user_detail", null );
        res.moveToFirst();
        while(res.isAfterLast() == false)
        {
            array_list.add(res.getString(res.getColumnIndex(CONTACTS_COLUMN_USER_ID)));
            array_list.add(res.getString(res.getColumnIndex(CONTACTS_COLUMN_USER_PWD)));
            array_list.add(res.getString(res.getColumnIndex(CONTACTS_COLUMN_FF_CODE)));
            array_list.add(res.getString(res.getColumnIndex(CONTACTS_COLUMN_FF_NAME)));
            array_list.add(res.getString(res.getColumnIndex(CONTACTS_COLUMN_TERR_CODE)));
            array_list.add(res.getString(res.getColumnIndex(CONTACTS_COLUMN_DG_CODE)));
            array_list.add(res.getString(res.getColumnIndex(CONTACTS_COLUMN_DIST_CODE)));
            array_list.add(res.getString(res.getColumnIndex(CONTACTS_COLUMN_FF_MOB)));
            array_list.add(res.getString(res.getColumnIndex(CONTACTS_COLUMN_IMEI_NO)));

            res.moveToNext();
        }
        return array_list;
    }

    public static  String getCodeAndPassword(String ffCode)
    {
       Log.e("retrieving ff code", "yes");
       SQLiteDatabase db = null;
       //SQLiteDatabase db = getWritableDatabse();
       Cursor cursor =   db.query("user_detail", null, " ff_code=?" , new String[]{ffCode}, null, null, null);
       if(cursor.getCount()<1)
        {
            cursor.close();
            return "Not Exist";
        }
        Log.e("found ff code", "yes");
        cursor.moveToFirst();
        String ffcode= cursor.getString(cursor.getColumnIndex("ff_code"));
        return ffcode;
    }