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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.
The class hierarchy can be as deep as needed. The instance variables and methods are inherited down through the levels and can be redefined according to the requirement in a subclass. In general, the further down in the hierarchy a class appears, the more specialized its behavior.
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 ...
Class invariants are inherited, that is, "the invariants of all the parents of a class apply to the class itself." [1] Inheritance can allow descendant classes to alter implementation data of parent classes, so it would be possible for a descendant class to change the state of instances in a way that made them invalid from the viewpoint of the ...
A class can only inherit from a single class, but can mix-in as many traits as desired. Scala resolves method names using a right-first depth-first search of extended 'traits', before eliminating all but the last occurrence of each module in the resulting list. So, the resolution order is: [D, C, A, B, A], which reduces down to [D, C, B, A].
Classes may inherit from other classes, so they are arranged in a hierarchy that represents "is-a-type-of" relationships. For example, class Employee might inherit from class Person. All the data and methods available to the parent class also appear in the child class with the same names.
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 ...