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C++ does not have the keyword 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 classes, the base class Rectangle, and the derived class Box.
A notable language in which this is a fairly common paradigm is C++. C# supports return type covariance as of version 9.0. [1] Covariant return types have been (partially) allowed in the Java language since the release of JDK5.0, [2] so the following example wouldn't compile on a previous release:
In the Java virtual machine, internal type signatures are used to identify methods and classes at the level of the virtual machine code. Example: The method String String. substring (int, int) is represented in bytecode as Ljava / lang / String. substring (II) Ljava / lang / String;. The signature of the main method looks like this: [2]
The concept of the virtual function solves the following problem: 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.
To override the default behavior, one simply qualifies a method call with the desired class definition. Perl uses the list of classes to inherit from as an ordered list. The compiler uses the first method it finds by depth-first searching of the superclass list or using the C3 linearization of the class hierarchy. Various extensions provide ...
Java, C++ (Since C++11) and D allow inheritance or overriding a class method to be prohibited by labeling a declaration of a class or method, respectively, with the keyword "final". In the book Effective Java, author Joshua Bloch writes (in item 17) that programmers should "Design and document for inheritance or else prohibit it".
Some languages require that method be specifically declared as virtual (e.g. C++), and in others, all methods are virtual (e.g. Java). An invocation of a non-virtual method will always be statically dispatched (i.e. the address of the function call is determined at compile-time).
When lexical scoping is used to infer this, the use of this in code, while not illegal, may raise warning bells to a maintenance programmer, although there are still legitimate uses of this in this case, such as referring to instance variables hidden by local variables of the same name, or if the method wants to return a reference to the current object, i.e. this, itself.