Introducing Visitor Objects in PHP 5 - Defining another sample class
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As I expressed earlier, I want to expand the practicality of the previous example by coding another sample class, which also accepts a visitor object. In this case, this new class is called "VisitedFile," and its signature is as follows:
// extend 'VisitedFile' class from abstract 'VisitedData' class
class VisitedFile extends VisitedData{
private $filePath;
public function __construct
($filePath='default_path/data.txt'){
$this->filePath=$filePath;
}
// add new line to data file
public function addLine($line){
if(!$fp=fopen($this->filePath,'a+')){
throw new Exception('Error opening data file');
}
fwrite($fp,$line."n");
fclose($fp);
}
// get file size
public function getSize(){
if(!$size=filesize($this->filePath)){
throw new Exception('Error determining size of data
file');
}
return $size;
}
// get number of file lines
public function getNumLines(){
if(!$numLines=count(file($this->filePath))){
throw new Exception('Error determining number of
lines for data file');
}
return $numLines;
}
// accepts 'visitator' object and call 'visitFile()' method
public function acceptVisitator(Visitator $visitator){
$visitator->visitFile($this);
}
}
As shown above, the functionality of the new "VisitedFile" class is only limited to saving plain strings to a given text file. However, my intention here is that you pay attention to the respective "acceptVisitator()" method, since it's closely similar to the previous one that you learned in the past section.
Also, on this occasion, the visitor will call its visiting method, and pass to it the visited object, with the purpose of getting additional information about it. As I said before, this model of object interaction is practically identical for all the cases where the visitor pattern is implemented. I hope you'll have no problem grasping this concept.
Okay, at this point you learned how to create two subclasses that accept visitor objects, but... how can these visitors be created? Do you have any clue about that? Well, to dissipate any possible questions, over the course of the next section, I'll show you how to define the structure of visitor objects.
To learn how this will be done, click on the link below and continue reading.
Next: Defining the structure of a visitor >>
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