Using a class to handle the output of another class

[Oli Thissen]

Hello everybody!

I'm having a little problem with the following: I wrote a class to
collect data (Let's call it DataCollector). Now I want the data to be
interpreted in various ways. My idea was to write an interface
(iVisualizer) so DataCollector could use every user defined
(MyVisualizer) class implementing it. Saying "MyVisualizer extends
DataCollector" is not an option, since the data should only be
collected once and then then being "rendered" by a variety of output
classes (to XML, to plain text, to PDF, etc.).

Here is the code example:

<php>
class DataCollector {
private $data

public function collectData ($someText) {
// Write data here
}

public function output($visualizer) {
$visualizer->output($this)
}
}

class MyVisualizer implements iVisualizer {
public function output ($dataCollector)
{
echo $dataCollector->data;
}
}

$a = new DataCollector();
$b = new MyVisualizer();
$a->collectData("foo");
$a->output($b);
</php>

Now, obviously calling "$a->output($b);" will get me in trouble, since
DataCollector::data is private. Making DataCollector::data public
would make it easy, but also "unsafe". Adding get & set methods will
add lots of methods, since $data is just an example for a large number
of properties.

I really hope to get some good ideas here. Thanks in advance!

Oli

[Jerry Stuckle]

Oli Thissen wrote:

Hello everybody!

I'm having a little problem with the following: I wrote a class to
collect data (Let's call it DataCollector). Now I want the data to be
interpreted in various ways. My idea was to write an interface
(iVisualizer) so DataCollector could use every user defined
(MyVisualizer) class implementing it. Saying "MyVisualizer extends
DataCollector" is not an option, since the data should only be
collected once and then then being "rendered" by a variety of output
classes (to XML, to plain text, to PDF, etc.).

Here is the code example:

<php>
class DataCollector {
private $data

public function collectData ($someText) {
// Write data here
}

public function output($visualizer) {
$visualizer->output($this)
}
}

class MyVisualizer implements iVisualizer {
public function output ($dataCollector)
{
echo $dataCollector->data;
}
}

$a = new DataCollector();
$b = new MyVisualizer();
$a->collectData("foo");
$a->output($b);
</php>

Now, obviously calling "$a->output($b);" will get me in trouble, since
DataCollector::data is private. Making DataCollector::data public
would make it easy, but also "unsafe". Adding get & set methods will
add lots of methods, since $data is just an example for a large number
of properties.

I really hope to get some good ideas here. Thanks in advance!

Oli

First of all, a Visualizer object is not a "type of" DataCollector, so
trying to derive Visualizer from DataCollector would be incorrect.

You have the data items are private, as they should be (encapsulation).
So you need getter and setter methods for each one. The getter
methods return copies, and the setter methods validate the data before
actually storing it.

Yes, sometimes it means a bunch of setters and getter methods. But it's
also the correct way to do it.

--
==================
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
js*******@attglobal.net
==================

[ZeldorBlat]

On Nov 10, 3:18 pm, Jerry Stuckle <[e-mail]:

Oli Thissen wrote:

Hello everybody!

I'm having a little problem with the following: I wrote a class to
collect data (Let's call it DataCollector). Now I want the data to be
interpreted in various ways. My idea was to write an interface
(iVisualizer) so DataCollector could use every user defined
(MyVisualizer) class implementing it. Saying "MyVisualizer extends
DataCollector" is not an option, since the data should only be
collected once and then then being "rendered" by a variety of output
classes (to XML, to plain text, to PDF, etc.).

Here is the code example:

<php>
class DataCollector {
private $data

public function collectData ($someText) {
// Write data here
}

public function output($visualizer) {
$visualizer->output($this)
}
}

class MyVisualizer implements iVisualizer {
public function output ($dataCollector)
{
echo $dataCollector->data;
}
}

$a = new DataCollector();
$b = new MyVisualizer();
$a->collectData("foo");
$a->output($b);
</php>

Now, obviously calling "$a->output($b);" will get me in trouble, since
DataCollector::data is private. Making DataCollector::data public
would make it easy, but also "unsafe". Adding get & set methods will
add lots of methods, since $data is just an example for a large number
of properties.

I really hope to get some good ideas here. Thanks in advance!

Oli

First of all, a Visualizer object is not a "type of" DataCollector, so
trying to derive Visualizer from DataCollector would be incorrect.

You have the data items are private, as they should be (encapsulation).
So you need getter and setter methods for each one. The getter
methods return copies, and the setter methods validate the data before
actually storing it.

Yes, sometimes it means a bunch of setters and getter methods. But it's
also the correct way to do it.

Everything Jerry said is correct. I would add that, if you have a lot
of private members (i.e. columns from a table in a database) you can
save yourself some work by taking advantage of the __get() and __set()
magic methods:

<http://www.php.net/manual/en/language.oop5.magic.php>

That way you don't need to write individual getters and setters for
every piece of data stored in your object.