Defining Public and Protected Methods with Member Visibility in PHP 5 - Calling methods of a class globally
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Working with public class methods is an extremely simple process that can be grasped in a few minutes, even by inexperienced developers. Naturally, if you've used classes in PHP 4, then you should know that all the methods you define are public by default, since there's no way to prevent them from being accessed globally.
However, as you may have noticed, it's possible to use the "public" keyword to specify the visibility of a method in PHP 5. What's more, if no visibility is assigned to a method, then it will be declared public also by default.
Let me stop discussing theory for a moment and show you a practical example, where you'll learn how to declare and implement a few public methods. To do this, I'm going to use the familiar "DataSaver" class that you saw in the previous articles of the series. The signature is listed below:
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, all of the methods incorporated into the above class are declared public, which means that they can be called directly from outside the class in question. To understand this concept, look at the following script, which shows how to invoke some methods of the sample "DataSaver" class in the global scope:
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
$dataSaver->save();
// call public methods
echo 'Target file is the following : '.$dataSaver->getfilePath().'<br />';
echo 'Data for being saved to target file is the following : '.$dataSaver->getData();
/* displays the following
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();
}
So far, there's nothing unexpected. As you can see, because the "save()," "getFilePath()," and "getData()" methods of the above sample class have been declared public, they can be invoked directly from outside the mentioned class and the PHP interpreter won't trigger any fatal errors.
Using public methods with PHP 5 is a no-brainer process, but even so, you should be very careful when declaring the visibility of methods that make up your own classes, particularly if you don't want them to be accessed in the global context.
Well, assuming that you grasped how to work with public class methods, it's time to move forward and continue with this educational journey. Therefore, in the course of the following section, I'm going to utilize the same data saving class that you saw before in order to explain how to declare and implement protected methods.
To learn the complete details on this useful topic, please go ahead and read the next few lines. They're only one click away.
Next: Declaring and implementing protected methods within PHP 5 classes >>
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