Before I start teaching you how to define and implement private class methods in PHP 5, let me spend a brief moment refreshing some important concepts that were deployed in the last article of this series. I demonstrated how to create a trivial class that used a couple of methods, which were declared protected.

As you'll surely recall, protected methods are preceded by the "protected" PHP keyword and can only be called from inside the originating class, or from inside the eventual subclasses. But, as always, this concept will be better grasped if you look at the following example, which shows what happens when a protected method defined within a sample class is called in the global scope.

Here's the pertinent code sample:

class DataSaver{

private $filePath;

private $data;

public function __construct($data,$filePath){

if(!$data||strlen($data)>1024){

throw new Exception('Invalid data for being saved to target file.');

}

if(!file_exists($filePath)){

throw new Exception('Invalid target file.');

}

$this->data=$data;

$this->filePath=$filePath;

}

// save data to target file

public function save(){

if(!$fp=fopen($this->filePath,'w')){

throw new Exception('Error opening target file.');

}

if(!fwrite($fp,$this->data)){

throw new Exception('Error writing data to target file.');

}

fclose($fp);

}

// get target file via an accessor

protected function getFilePath(){

return $this->filePath;

}

// get data via an accessor

protected function getData(){

return $this->data;

}

}

try{

// create new instance of 'DataSaver' class

$dataSaver=new DataSaver('This string of data will be saved to a target file!','datafile.txt');

// save data to target file

$dataSaver->save();

// call protected methods

echo 'Target file is the following : '.$dataSaver->getfilePath().'<br />';

echo 'Data for being saved to target file is the following : '.$dataSaver->getData();

/* displays the following

Fatal error: Call to protected method DataSaver::getfilePath() from context '' in path/to/file/

*/

}

catch(Exception $e){

echo $e->getMessage();

exit();

}

As you can see, the above hands-on example is a no-brainer. In this particular case, I used the familiar "DataSaver" class that you learned in previous tutorials in order to demonstrate how the PHP interpreter reacts when the protected methods of the class in question are called from outside of it. It triggers a fatal error.

Well, after examining the previous code sample, don't you feel a bit more relaxed? You should, because at this point you've been familiarized with using a couple of protected methods within a basic data saving class.

Considering this promising scenario, it's time to jump forward and continue learning more useful things concerning the utilization of member visibility with PHP 5. Therefore, as I stated in the introduction, in the course of the following section, I'm going to teach you how to use the same sample class listed previously, but this time to declare and implement private methods.

Are you curious about how this will be done? Don't hesitate to read the next few lines. I'll be there, waiting for you.