Editing Method overriding (section)

===C++===

[[C++]] does not have the keyword {{Cpp|super}} that a subclass can use in Java to invoke the superclass version of a method that it wants to override. Instead, the name of the parent or base class is used followed by the [[scope resolution operator]]. For example, the following code presents two [[Class (computer science)|classes]], the base class {{Cpp|Rectangle}}, and the derived class {{Cpp|Box}}. {{Cpp|Box}} overrides the {{Cpp|Rectangle}} class's {{Cpp|Print}} method, so as also to print its height.<ref name="malik">Malik 2006, p. 676</ref>

<syntaxhighlight lang="cpp">
#include <iostream>

//---------------------------------------------------------------------------
class Rectangle {
 public:
  Rectangle(double l, double w) : length_(l), width_(w) {}
  virtual void Print() const;

 private:
  double length_;
  double width_;
};

//---------------------------------------------------------------------------
void Rectangle::Print() const {
  // Print method of base class.
  std::cout << "Length = " << length_ << "; Width = " << width_;
}

//---------------------------------------------------------------------------
class Box : public Rectangle {
 public:
  Box(double l, double w, double h) : Rectangle(l, w), height_(h) {}
  void Print() const override;

 private:
  double height_;
};

//---------------------------------------------------------------------------
// Print method of derived class.
void Box::Print() const {
  // Invoke parent Print method.
  Rectangle::Print();
  std::cout << "; Height = " << height_;
}
</syntaxhighlight>

The method {{Cpp|Print}} in class {{Cpp|Box}}, by invoking the parent version of method {{Cpp|Print}}, is also able to output the private [[Variable (programming)|variables]] {{Cpp|length}} and {{Cpp|width}} of the base class. Otherwise, these variables are inaccessible to {{Cpp|Box}}.

The following [[Statement (programming)|statements]] will [[Object (computer science)|instantiate]] objects of type {{Cpp|Rectangle}} and {{Cpp|Box}}, and call their respective {{Cpp|Print}} methods:

<syntaxhighlight lang="cpp">
int main(int argc, char** argv) {
  Rectangle rectangle(5.0, 3.0);

  // Outputs: Length = 5.0; Width = 3.0
  rectangle.Print();

  Box box(6.0, 5.0, 4.0);

  // The pointer to the most overridden method in the vtable in on Box::print,
  // but this call does not illustrate overriding.
  box.Print();

  // This call illustrates overriding.
  // outputs: Length = 6.0; Width = 5.0; Height= 4.0
  static_cast<Rectangle&>(box).Print();
}
</syntaxhighlight>

In [[C++11]], similar to Java, a method that is declared <code>final</code> in the super class cannot be overridden; also, a method can be declared <code>override</code> to make the compiler check that it overrides a method in the base class.