The Basicsclass
Every class definition begins with the
keyword class, followed by a class name,
followed by a pair of curly braces which enclose the definitions
of the class's properties and methods.
The class name can be any valid label which is a not a
PHP reserved word. A valid class
name starts with a letter or underscore, followed by any number of
letters, numbers, or underscores. As a regular expression, it
would be expressed thus:
[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*.
A class may contain its
own constants, variables
(called "properties"), and functions (called "methods").
Simple Class definition
var;
}
}
?>
]]>
The pseudo-variable $this is available when a
method is called from within an object
context. $this is a reference to the calling
object (usually the object to which the method belongs, but
possibly another object, if the method is called
statically from the context
of a secondary object).
Some examples of the <varname>$this</varname> pseudo-variable
foo();
// Note: the next line will issue a warning if E_STRICT is enabled.
A::foo();
$b = new B();
$b->bar();
// Note: the next line will issue a warning if E_STRICT is enabled.
B::bar();
?>
]]>
&example.outputs;
new
To create an instance of a class, a new object must be created and
assigned to a variable. An object will always be assigned when
creating a new object unless the object has a
constructor defined that throws an
exception on error. Classes
should be defined before instantiation (and in some cases this is a
requirement).
Creating an instance
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In the class context, it is possible to create a new object by
new self and new parent.
When assigning an already created instance of a class to a new variable, the new variable
will access the same instance as the object that was assigned. This
behaviour is the same when passing instances to a function. A copy
of an already created object can be made by
cloning it.
Object Assignment
var = '$assigned will have this value';
$instance = null; // $instance and $reference become null
var_dump($instance);
var_dump($reference);
var_dump($assigned);
?>
]]>
&example.outputs;
string(30) "$assigned will have this value"
}
]]>
extends
A class can inherit the methods and properties of another class by
using the keyword extends in the class
declaration. It is not possible to extend multiple classes; a
class can only inherit from one base class.
The inherited methods and properties can be overridden by
redeclaring them with the same name defined in the parent
class. However, if the parent class has defined a method
as final, that method
may not be overridden. It is possible to access the overridden
methods or static properties by referencing them
with parent::.
Simple Class Inheritance
displayVar();
?>
]]>
&example.outputs;