As I stated in the section that you just read, below I included a new group of data checking classes, created specifically for validating alphabetic and alphanumeric values, as well as email addresses. You should notice that I also created an additional class that verifies the validity of a given email address that can be used with Windows-based machines, in case you're working with that operating system.

Having clarified that, here are the signatures that correspond to the aforementioned classes. They look like this:

// define 'AlphabeticValidator class
class AlphabeticValidator extends DataValidator{
   public function validate($inputData){
     if(!$inputData||!preg_match("/^[a-zA-Z]+$/",$inputData)){
       return false;
     }
     return true;
   }
}

// define 'AlphanumericValidator' class
class AlphanumericValidator extends DataValidator{
   public function validate($inputData){
     if(!$inputData||!preg_match("/^[a-zA-Z0-9]+$/",$inputData)){
       return false;
     }
     return true;
   }
}

// define 'EmailValidator' class
class EmailValidator extends DataValidator{
   public function validate($inputData){
     if(!$inputData||!preg_match("/.+@.+..+./",$inputData)||!
checkdnsrr(array_pop(explode("@",$inputData)),"MX")){
       return false;
     }
     return true;
   }
}

// define 'EmailValidatorWin' class
class EmailValidatorWin extends DataValidator{
   public function validate($inputData){
     if(!$inputData||!preg_match("/.+@.+..+./",$inputData)||!
$this->windnsrr(array_pop(explode("@",$inputData)),"MX")){
       return false;
     }
     return true;
   }
   private function windnsrr($hostName,$recType=''){
     if($hostName){
       if($recType=='')$recType="MX";
       exec("nslookup -type=$recType $hostName",$result);
       foreach($result as $line){
         if(preg_match("/^$hostName/",$line)){
           return true;
         }
       }
       return false;
     }
     return false;
   }
}

As you can see, the above data validation classes look very similar to the ones created in the previous section. Logically, the only difference to spot here is with reference to the diverse implementations of the respective "validate()" method. It's different for each class.

Again, you'll realize that I'm playing with the concept of polymorphism to expand the capacity of this data checking application, something that you can try for yourself if you want to verify additional types of data. As you learned previously, the process is indeed simple.

Well, at this stage I have built a decent number of data checking classes for validating a broad range of user-supplied entries by taking advantage of polymorphism. However, there's still a missing piece in this schema, since a programmatic mechanism is required here to demonstrate more clearly how to use the polymorphic facet exposed by all these classes.

So, what is that piece? In short, I plan to use a factory class so I can easily spawn a certain number of validating objects. These objects will be used to check different types of user-supplied data. Of course, I'll keep the source code of this factory class extremely simple, because I don't want to bother you with irrelevant details. Here's how this class looks:

// define 'ValidatorFactory' class
class ValidatorFactory{
   public function createValidator($validator){
     return new $validator();
   }
}

The above factory class returns to client code a specific kind of validating object, in accordance with the incoming $validator parameter passed to its respective "createValidator()" method.

So far, so good. At this point, I have shown you the complete signatures that correspond to all the validation classes that you learned before, in conjunction with an additional factory class. Therefore, the next step will consist of developing a hands-on example, where you'll see how all these classes can be put to work together.

Want to see how this practical example will be developed? Keep reading, please.