Using Subclasses and Accessors with Member Visibility to Protect PHP 5 Class Data - Retrieving the values of private properties using accessors
(Page 4 of 4 )
During the previous section, you learned a simple -- yet crucial -- concept: the private properties of a class can only be accessed from inside of the class. However, it's possible to play around with this theoretical definition and develop yet another example that shows how the properties in question can be retrieved by way of an accessor method.
To perform this task, I'm going to use the same "DataSaver" class that you saw previously, which, as you'll surely recall, does have a couple of these accessor methods. If this doesn't ring any bells, here's the signature of this class:
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
public function getFilePath(){
return $this->filePath;
}
// get data via an accessor
public function getData(){
return $this->data;
}
}
As you can see, the above data saving class has been provided with a couple of accessors, called "getFilePath()" and "getData()" respectively. With these methods available, I'm going to create a simple script that shows how to use them in order to access the private properties of the class.
Having said that, here's the script:
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
$dataSaver->save();
// print value of private properties
echo 'Target file is the following : '.$dataSaver->getFilePath().'<br />';
echo 'Data for being saved to target file is the following : '.$dataSaver->getData();
/* displays the following
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();
}
As shown by the previous code snippet, it's perfectly possible to retrieve the values that correspond to the private properties of the "DataSaver" class by using the respective accessors. The reason is extremely simple: the methods access the properties from inside the class!
Of course, this concept may seem pretty obvious, particularly if you have a lot of experience working with classes in PHP. But if you're just getting started using its object model, the previous example might help you understand how to work with private properties.
Finally, with all of these code samples at your disposal, don't excuse yourself from practicing with private class properties in PHP 5!
Final thoughts
In this third episode of the series I concluded this quick overview of working with public, protected, and private class properties. Nonetheless, I'm only scratching the surface when it comes to exploring the advantages of using member visibility in PHP 5; the language permits you to use this same feature with the methods of a class as well. Thus, in the upcoming article, I'll explain how to implement this handy feature in several class methods.
Now that you've been warned about the subject of the next part, you can't miss it!
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