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PHP 5 introduced private and protected member variables and methods, along with abstract classes and final classes as well as abstract methods and final methods. It also introduced a standard way of declaring constructors and destructors, similar to that of other object-oriented languages such as C++, and a standard exception handling model.
There are methods that a subclass cannot override. For example, in Java, a method that is declared final in the super class cannot be overridden. Methods that are declared private or static cannot be overridden either because they are implicitly final. It is also impossible for a class that is declared final to become a super class. [9]
In most quarters, class inheritance for the sole purpose of code reuse has fallen out of favor. [citation needed] The primary concern is that implementation inheritance does not provide any assurance of polymorphic substitutability—an instance of the reusing class cannot necessarily be substituted for an instance of the inherited class.
This can require significantly less programming effort if the base class contains many methods providing default behavior and only a few of them need to be overridden within the derived class. For example, in the C# code below, the variables and methods of the Employee base class are inherited by the HourlyEmployee and SalariedEmployee derived ...
In object-oriented programming, when a derived class inherits from a base class, an object of the derived class may be referred to via a pointer or reference of the base class type instead of the derived class type. If there are base class methods overridden by the derived class, the method actually called by such a reference or pointer can be ...
Also, derived classes can override inherited methods if the language allows. Not all languages support multiple inheritance. For example, Java allows a class to implement multiple interfaces, but only inherit from one class. [22] If multiple inheritance is allowed, the hierarchy is a directed acyclic graph (or DAG for short), otherwise it is a ...
An object's virtual method table will contain the addresses of the object's dynamically bound methods. Method calls are performed by fetching the method's address from the object's virtual method table. The virtual method table is the same for all objects belonging to the same class, and is therefore typically shared between them.
To use PHP with an HTML form, the URL of the PHP script is specified in the action attribute of the form tag. The target PHP file then accesses the data passed by the form through PHP's $_POST or $_GET variables, depending on the value of the method attribute used in the form. Here is a basic form handler PHP script that will display the ...