public String getSinlgeEntry(String userName) {
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.query("table_name", null, " USERNAME=?", new String[]{userName}, null, null, null);
    if (cursor.getCount() < 1) // UserName Not Exist
    {
        cursor.close();
        return "NOT EXIST";
    }
    cursor.moveToFirst();
    String password = cursor.getString(cursor.getColumnIndex("PASSWORD"));
    cursor.close();
    return password;
}

DatabaseClassName myDb = new DatabaseClassName(this);

String result1 = myDb.getSinlgeEntry(user_entered_username);