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<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.14 $ -->
<sect1 id="language.oop5.basic">
<title>The Basics</title>
<sect2 id="language.oop5.basic.class">
<title>class</title>
<para>
Every class definition begins with the keyword class, followed by a class
name, which can be any name that isn't a <link linkend="reserved">reserved</link>
word in PHP. Followed by a pair of curly braces, of
which contains the definition of the classes members and methods. A
pseudo-variable, <varname>$this</varname> is available when a method is
called from within an object context. <varname>$this</varname> is a
reference to the calling object (usually the object to which the method
belongs, but can be another object, if the method is called
<link linkend="language.oop5.static">statically</link> from the context
of a secondary object). This is illustrated in the following example:
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
class A
{
function foo()
{
if (isset($this)) {
echo '$this is defined (';
echo get_class($this);
echo ")\n";
} else {
echo "\$this is not defined.\n";
}
}
}
class B
{
function bar()
{
A::foo();
}
}
$a = new A();
$a->foo();
A::foo();
$b = new B();
$b->bar();
B::bar();
?>
]]>
</programlisting>
&example.outputs;
<screen>
<![CDATA[
$this is defined (a)
$this is not defined.
$this is defined (b)
$this is not defined.
]]>
</screen>
</informalexample>
</para>
<example>
<title>Simple Class definition</title>
<programlisting role="php">
<![CDATA[
<?php
class SimpleClass
{
// member declaration
public $var = 'a default value';
// method declaration
public function displayVar() {
echo $this->var;
}
}
?>
]]>
</programlisting>
</example>
</sect2>
<sect2 id="language.oop5.basic.new">
<title>new</title>
<para>
To create an instance of an object, a new object must be created and
assigned to a variable. An object will always be assigned when
creating a new object unless the object has a
<link linkend="language.oop5.decon">constructor</link> defined that throws an
<link linkend="language.exceptions">exception</link> on error.
</para>
<example>
<title>Creating an instance</title>
<programlisting role="php">
<![CDATA[
<?php
$instance = new SimpleClass()
?>
]]>
</programlisting>
</example>
<para>
When assigning an already created instance of an object to a new variable, the new variable
will access the same instance as the object that was assigned. This
behaviour is the same when passing instances to a function. A new instance
of an already created object can be made by
<link linkend="language.oop5.cloning">cloning</link> it.
</para>
<example>
<title>Object Assignment</title>
<programlisting role="php">
<![CDATA[
<?php
$assigned = $instance;
$reference =& $instance;
$instance->var = '$assigned will have this value';
$instance = null; // $instance and $reference become null
var_dump($instance);
var_dump($reference);
var_dump($assigned);
?>
]]>
</programlisting>
&example.outputs;
<screen>
<![CDATA[
NULL
NULL
object(SimpleClass)#1 (1) {
["var"]=>
string(30) "$assigned will have this value"
}
]]>
</screen>
</example>
</sect2>
<sect2 id="language.oop5.basic.extends">
<title>extends</title>
<para>
A class can inherit methods and members of another class by using the
extends keyword in the declaration. It is not possible to extend multiple
classes, a class can only inherit one base class.
</para>
<para>
The inherited methods and members can be overridden, unless the parent
class has defined a method as <link linkend="language.oop5.final">final</link>,
by redeclaring them within the same name defined in the parent class.
It is possible to access the overrided method or members by
referencing them with <link linkend="language.oop5.paamayim-nekudotayim">parent::</link>
</para>
<example>
<title>Simple Class Inherintance</title>
<programlisting role="php">
<![CDATA[
<?php
class ExtendClass extends SimpleClass
{
// Redefine the parent method
function displayVar()
{
echo "Extending class\n";
parent::displayVar();
}
}
$extended = new ExtendClass();
$extended->displayVar();
?>
]]>
</programlisting>
&example.outputs;
<screen>
<![CDATA[
Extending class
a default value
]]>
</screen>
</example>
</sect2>
</sect1>
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