ZEND PHP 5 Certification STUDY GUIDE

124 ” Object Oriented Programming in PHP
Strict Standards: Accessing static property foo::$bar as non static in
PHPDocument1 on line 1
It is necessary for the static definition to follow the visibility definition; if no visibility
definition is declared, the static method or property is considered public.
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Class Constants
Class constants work in the same way as regular constants, except they are scoped
within a class. Class constants are public, and accessible from all scopes; for example,
the following script will output Hello World:
class foo {
const BAR = "Hello World";
}
echo foo::BAR;
Note that class constants suffer from the same limitations as regular constants—therefore,
they can only contain scalar values.
Class constants have several advantages over traditional constants: since they are
encapsulated in a class, they make for much cleaner code, and they are significantly
faster than those declared with the define() construct.
Interfaces & Abstract Classes
Yet another new feature added to PHP 5 is that of Interfaces and Abstract classes.
These are both used to create a series of constraints on the base design of a group of
classes. An abstract class essentially defines the basic skeleton of a specific type of
encapsulated entity—for example, you can use an abstract class to define the basic
concept of “car” as having two doors, a lock and a method that locks or unlocks the
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