Every class definition begins with the keyword class, followed by a class name, which can be any name that isn't a reserved word in PHP. Followed by a pair of curly braces, of which contains the definition of the classes members and methods. A 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 can be another object, if the method is called statically from the context of a secondary object). This is illustrated in the following example: foo(); A::foo(); $b = new B(); $b->bar(); B::bar(); ?> ]]> &example.outputs; var; } } ?> ]]> To create an instance of an object, a new object must be created and assigned to a variable. An object will always be assigned when creating a new object unless the object has a constructor defined that throws an exception on error. ]]> When assigning an already created instance of an object to a new variable, the new variable will access the same instance as the object that was assigned. This behaviour is the same when passing instances to a function. A new instance of an already created object can be made by cloning it. var = '$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" } ]]> 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. The inherited methods and members can be overridden, unless the parent class has defined a method as final, 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 parent:: displayVar(); ?> ]]> &example.outputs;