A review of public and protected class properties in PHP 5 - PHP

In the introduction, I provided you with a quick reference regarding the use of public and protected class properties in PHP 5. However, I’d like to complement this theory with the hands-on examples developed in the preceding article of the series. This way, you can tackle this topic from a practical point of view.

Having said that, please take a look at the following code samples, which demonstrate how to use both public and protected properties using the same sample class. Here they are:

(example using public properties with a data saving class)

// define 'DataSaver' class (saves a string of data to a target file and their properties are defined public)

class DataSaver{

public $filePath;

public $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

public function getFilePath(){

return $this->filePath;

}

// get data via an accessor

public 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();

// print value of public properties

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

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

/* displays the following

Target file is the following : datafile.txt

Data for being saved to target file is the following : This string of data will be saved to a target file!

*/

}

catch(Exception $e){

echo $e->getMessage();

exit();

}

(example using protected properties with a data saving class -- properties are defined protected)

class DataSaver{

protected $filePath;

protected $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

public function getFilePath(){

return $this->filePath;

}

// get data via an accessor

public 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();

// print value of protected properties

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

echo 'Data for being saved to target files is the following : '.$dataSaver->data;

/* displays the following fatal error with the first property

Fatal error: Cannot access protected property DataSaver::$filePath in path/to/file/

*/

/* displays the following fatal error with the second property

Fatal error: Cannot access protected property DataSaver::$data in path/to/file/

*/

}

catch(Exception $e){

echo $e->getMessage();

exit();

}

At this point, you should feel pretty satisfied, since the hands-on examples listed above give you a clear idea of how to work with public and protected properties using the same sample “DataSaver” class. In the first case, you can see that the properties in question are accessible in the global scope, since they’ve been declared public. In the second example, the PHP interpreter triggers a few fatal errors when trying to access the properties publicly, because the mentioned properties have been defined as protected. Not too hard to grasp, is it?

So far, so good. Now that you've hopefully learned the basic concepts that surround the use of public and protected properties with PHP 5 classes, it’s time to explore more useful aspects of the utilization of member visibility.

Even when protected properties can’t be accessed directly in the global scope, they’re not restricted when used by one or more subclasses derived from the pertinent parent. Therefore, in the following section, I’m going to create another practical example for you that will recreate the scenario described above.

In order to see how this brand new example will be developed, go ahead and read the next few lines. They’re only one click away.