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Lesson 16 - Putting PHP interfaces into practice - GuestBook

In the previous lesson, Interfaces and abstract classes in PHP, we went over the theoretical aspects of interfaces and abstract classes. Now, as is tradition here at, we're going to put what we learned to proper use.


We'll program a simple guestbook or rather a shout-board. I'm sure you all have seen widgets like this somewhere on the web. They're a spot on the website, where the last couple of messages are displayed along with a form that submits a new message. To protect us from spam, our messenger will use a captcha (an antispam mechanism). Our captcha will require an interface because we're going to make it modular.

Create a new project folder, wherein you'll create a "classes" folder and an index.php file.


First and foremost, we'll set up the database. Create a new table and name it "message". This table will contain guestbook messages, and will have the following columns:

  • message_id (int, primary, AI)
  • created (DATETIME)
  • name (varchar 50)
  • content (TEXT)

Add the table using PHPMyAdmin:

MySQL structure of guestbook database

Alternatively, you can use the following creation script:


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Article description

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In this lesson, we'll put our knowledge of OOP in PHP to the test by using interfaces to create a guestbook and modular captchas.

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Article has been written for you by David Capka Hartinger
The author is a programmer, who likes web technologies and being the lead/chief article writer at He shares his knowledge with the community and is always looking to improve. He believes that anyone can do what they set their mind to.
Unicorn university David learned IT at the Unicorn University - a prestigious college providing education on IT and economics.