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Difference between Abstraction and Encapsulation

OOP

Encapsulation : Wrapping up of data and methods into a single unit is called Encapsulation (e.g. Class)
Abstraction : It is an act of representing only the essential things without including background details. (e.g. Interface)

Real world example
Abstraction : You’ll never buy a “device”, but always buy something more specific : iPhone, Nokia 3310… Here, iPhone, and N3310 are concrete things, device is abstract.
Encapsulation : you’ve got several devices, all of them have got an USB port. You don’t know what kind of printed circuit they have, you just have to know you’ll be able to plug an USB cable onto.

Abstraction is a concept, which is allowed by encapsulation. You can do encapsulation without using abstraction, but if you wanna use some abstraction in your projects, you’ll need encapsulation.

Benefits of Abstraction :
Advantages of abstraction are the hiding of implementation details, component reuse, extensibility, and testability.

When we hide implementation details, we reveal a cleaner, more comprehensible and usable interface to our users.
We are separating our interface from our implementation, and this makes component reuse more practical.

Benefits of Encapsulation :

  • In Encapsulation fields of a class can be read-only or can be write-only.
  • A class can have control over in its fields.
  • A class can change data type of its fields anytime but users of this class do not need to change any code.

We can see the use of Encapsulation by using properties. The property has two accessor get and set. The get accessor returns the value of the some property field. The set accessor sets the value of the some property field with the contents of “value”.  Properties can be made read-only. This is accomplished by having only a get accessor in the property implementation.

 

 

upgrade PHP to PHP 5.4 on CentOS 6.5 on Parallels Plesk Panel 11.5 from a remi repository

linux

1. Install epel and remi repositories:

# wget http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm
# wget http://rpms.famillecollet.com/enterprise/remi-release-6.rpm
# sudo rpm -Uvh remi-release-6*.rpm epel-release-6*.rpm

2. Enable remi repository:
In the [remi] section of the file, set the “enabled” option to 1.

# sudo vi /etc/yum.repos.d/remi.repo

3. Upgrade PHP with this command:

# yum install php

Installation of Other modules and extensions for php 5.4.x

# yum search imagick
# yum install php-pecl-imagick.x86_64

# yum search soap
# yum install php-soap.x86_64

# yum search git
# yum install git.x86_64

# yum search nodejs
# yum install nodejs.x86_64

# yum search python
# yum install python.x86_64

# reboot

# /etc/init.d/httpd restart

# yum search denyhosts
# yum install denyhosts

For more details regarding denyhosts read this post

Installation of ionCube for PHP 5.4 (optional)

1. Download ionCube: For x32:

# wget http://downloads2.ioncube.com/loader_downloads/ioncube_loaders_lin_x86.zip

For x64:

# wget http://downloads2.ioncube.com/loader_downloads/ioncube_loaders_lin_x86-64.zip

2. Unzip file.
3. Copy ioncube_loader_lin_5.4.so to PHP extensions folder:

# sudo cp ioncube/ioncube_loader_lin_5.4.so /usr/lib/php/modules/

4. Set SELinux attributes:

# sudo chcon -u system_u -t textrel_shlib_t /usr/lib/php/modules/ioncube_loader_lin_5.4.so

5. Switch on ionCube in PHP config:

# echo "zend_extension=/usr/lib/php/modules/ioncube_loader_lin_5.4.so" >> /etc/php.d/zend_extensions_psa.ini

6. Check functioning of ionCube:

# php -r 'phpinfo();' | grep -i ioncube

You can also test ionCube Loader by using the helper PHP script “loader-wizard.php” that’s included in the ionCube Loader archive.

Compute similarity between two strings in MYSQL using Levenshtein algorithm

MYSQL, SQL 
DELIMITER $$
  CREATE FUNCTION levenshtein( s1 VARCHAR(255), s2 VARCHAR(255) )
  RETURNS INT
  DETERMINISTIC
  BEGIN
    DECLARE s1_len, s2_len, i, j, c, c_temp, cost INT;
    DECLARE s1_char CHAR;
    -- max strlen=255
    DECLARE cv0, cv1 VARBINARY(256);
    SET s1_len = CHAR_LENGTH(s1), s2_len = CHAR_LENGTH(s2), cv1 = 0x00, j = 1, i = 1, c = 0;
    IF s1 = s2 THEN
      RETURN 0;
    ELSEIF s1_len = 0 THEN
      RETURN s2_len;
    ELSEIF s2_len = 0 THEN
      RETURN s1_len;
    ELSE
      WHILE j <= s2_len DO
        SET cv1 = CONCAT(cv1, UNHEX(HEX(j))), j = j + 1;
      END WHILE;
      WHILE i <= s1_len DO
        SET s1_char = SUBSTRING(s1, i, 1), c = i, cv0 = UNHEX(HEX(i)), j = 1;
        WHILE j <= s2_len DO
          SET c = c + 1;
          IF s1_char = SUBSTRING(s2, j, 1) THEN
            SET cost = 0; ELSE SET cost = 1;
          END IF;
          SET c_temp = CONV(HEX(SUBSTRING(cv1, j, 1)), 16, 10) + cost;
          IF c > c_temp THEN SET c = c_temp; END IF;
          SET c_temp = CONV(HEX(SUBSTRING(cv1, j+1, 1)), 16, 10) + 1;
          IF c > c_temp THEN
            SET c = c_temp;
          END IF;
          SET cv0 = CONCAT(cv0, UNHEX(HEX(c))), j = j + 1;
        END WHILE;
        SET cv1 = cv0, i = i + 1;
      END WHILE;
    END IF;
    RETURN c;
  END$$
DELIMITER ;

Helper Function to find Ration in Percentage


DELIMITER $$
CREATE FUNCTION levenshtein_ratio( s1 VARCHAR(255), s2 VARCHAR(255) )
  RETURNS INT
  DETERMINISTIC
  BEGIN
    DECLARE s1_len, s2_len, max_len INT;
    SET s1_len = LENGTH(s1), s2_len = LENGTH(s2);
    IF s1_len > s2_len THEN 
      SET max_len = s1_len; 
    ELSE 
      SET max_len = s2_len; 
    END IF;
    RETURN ROUND((1 - LEVENSHTEIN(s1, s2) / max_len) * 100);
END$$
DELIMITER ;

Sample Usage

SELECT levenshtein_ratio(company_name, 'Company Name here') as perc, company_name FROM `clients` order by perc desc
/*return company name with percentage matching order by matching percentage.*/

Installing DenyHosts on Centos 6.5, Plesk 11.5

linux

DenyHosts is a log-based intrusion prevention security tool for SSH servers written in Python. It prevents brute-force attacks on SSH servers by monitoring invalid login attempts in the authentication log and blocking the originating IP addresses. Upon discovering a repeated attack host, the /etc/hosts.deny file is updated to prevent future break-in attempts from that host.

Add the EPEL repository if it is not already installed.

# wget http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm
# sudo rpm -Uvh epel-release-6*.rpm

and then simply install denyhosts from EPEL repository by using following command.

# yum install denyhosts

Before starting DenyHosts, configure a white list of IPs which DenyHosts should never block.
DenyHosts uses TCP Wrappers. edit /etc/hosts.allow and add IPs or entire subnets 

sshd: 123.234.246.566
sshd: 192.168.0.0/255.255.255.0

Start DenyHosts

# service denyhosts start

Configure the OS to start DenyHosts at every boot

# chkconfig denyhosts on

IPs to white list should be added to /etc/hosts.allow.
IPs that DenyHosts blocks will be added to /etc/hosts.deny.
DenyHosts logs everything that it does to /var/log/denyhosts.
The DenyHosts configuration file is /etc/denyhosts.conf.
DenyHosts watches /var/log/secure for SSH login attempts.
Host IP can be added or removed from /etc/hosts.deny to block or unblock access.
Go through the DenyHosts configuration file (/etc/denyhosts.conf) and configure it to your liking. do not forget to restart DenyHosts after changes in this file. 

# service denyhosts restart

Doctrine 2 ORM – Understanding of relationship/references between entities

Doctrine, Zend Framework,

Understanding of Reference and specially which site is owning and which is inverse in entities, could be tricky to understand for some people. Doctrine ORM provide easy way without having too much knowledge of database relationships.

References between objects are foreign keys in the database. You never have to work with the foreign keys directly, only with objects that represent the foreign key through their own identity.

For every foreign key you either have a Doctrine ManyToOne or OneToOne association. On the inverse sides of these foreign keys you can have OneToMany associations. Obviously you can have ManyToMany associations that connect two tables with each other through a join table with two foreign keys.

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