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Oracle Tips by Burleson |
Classes
and Methods
PHP allows OO (Object Oriented) programming much
in the same way as C++ or Java. This book will cover the object model
for PHP5 as it is much more complete than the one in PHP4, which is
gradually being phased out.
Object oriented programming is based on the idea
that related variables and methods used to access variables are placed
together in entities called classes. Classes can be thought of as new
data types, equivalent to strings or numbers. Classes have members and
methods. Members are variables and methods are functions. The
following is an example of a class:
#!/usr/local/bin/php
<?php
class example {
private $val;
public function printval() {
echo $this->val,”\n”;
}
public function getval() {
return($this->val);
}
public function setval($x) {
$this->val=$x;
}
function __construct($x) {
$this->val=$x;
}
}
$a=new example("This is an example class!");
$a->printval();
?>
When executed, this example prints out text:
$
./example11.php
This is an example class!
So, what does this class consist of? This class
has a private member $val. What does the word “private” mean?
Private means that the member is not accessible directly by functions
that do not belong to the class “example”. If an attempt is made to
add the following line of code to example11.php, an error will
occur:
$a->val="This
will cause an error";
The execution shows that there is something wrong:
$
./example11.php
This is an example class!
PHP Fatal error: Cannot access private property example::$val
in /home/mgogala/work/PHP/example11.php on line 21
Member $val is private and can only
be accessed by the methods of the class example. Member $val
could be declared as public, in which case, there would be no
problem with the assignment above. The method can also be declared
protected, which means that it can be accessed only by the methods
of the class “example” and the classes that inherit from the class
example. This is an important distinction: classes that extend
“inherit from” class “example” cannot access the private
members of the original class. Inheritance will be discussed in more
detail later.
The variable $this, which points to the
current variable of the given class should also be noted. It performs
the same function as the word “me” in the English language; it points
to ourselves. In PHP, the “me” is implemented as the variable $this.
Another thing to note are the getval() and
setval() methods. This is the recommended practice in OO
programming; always to have the data member private and always
create get/set access methods. Of course, this is a practice and not a
religion.
Sometimes there are valid reasons for having
public members. Any programming practice or principle can lead to
suboptimal and ugly programs when turned into a religion. Ultimately,
the programmer is the person to make the call. Any serious program
will have areas in which general recommendations have been sacrificed
to achieve greater code clarity or performance. All that is required
is that those trade-offs are made conscientiously and not as a result
of ignorance.
The last thing to note is the existence of the
__construct function. This function is called “constructor”. It
is not declared as public, protected or private,
which means that it is public. Constructor is invoked with the
operator new. Operator new constructs (genuine OO term
would be “instantiates”) a variable of type “example” (classes are new
data types).
There is also a __destructmethod although there is no delete operator. If so, when
does the __destruct method get executed? The __destruct
method gets executed when a variable belonging to the class example
falls out of the execution scope and there are no live references to
that variable. Now, few remarks for the users of PHP4 who have not yet
used PHP5:
-
Constructor in PHP4 was a function with the same
name as the class in which it constructs. For compatibility reasons
this type of constructor is still recognized, but deprecated.
-
PHP4 did not have member protection. Classes were
defined by using the keyword var which is synonymous with the
keyword public, again for compatibility reasons.
-
PHP4 did not have destructors.
See
code depot for complete scripts
The above book excerpt is from:
Easy Oracle
PHP
Create Dynamic Web Pages with Oracle Data
ISBN
0-9761573-0-6
Mladen Gogala
http://www.rampant-books.com/book_2005_2_php_oracle.htm
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