What is Method Overriding?

Method overriding is used in object-oriented programming within an inheritance hierarchy, and it occurs when a method defined in a superclass is redefined in a subclass. Usually, the subclass method does something different than the superclass method or expands on a capability of the superclass, but this doesn't have to be the case. Method overriding occurs whenever a superclass method is redefined in a subclass, regardless of the content of the redefined method. The redefined method signatures must be exactly the same.

For example, a class A might contain a method called "doSomething," and this method takes no input parameters. In addition, classes B and C might be subclasses of class A. Class B might contain a method called "doSomething," which takes no input parameters, and class C might contain a method "doSomething" that takes a number as an input parameter. In this example, only class B would demonstrate method overriding, because its "doSomething" method has the same method signature as its superclass, class A. The "doSomething" method in class C, on the other hand, demonstrates method overloading because it creates a completely new method.

Virtual inheritance in C++ is another example of method overriding. Virtual methods in superclasses might or might not be implemented, but any subclass definition of them is an instance of method overriding. When a method is overridden in a subclass, the method of the superclass is not called unless it is invoked explicitly. This specific way of calling an overridden method is often said to "hide" the superclass implementation.

Although method overriding is very flexible, not all methods can be overridden, and there are times when this rigidity might be preferable. In both Java and C++, specific keywords can be applied in method signatures to prevent a method from being overridden in a subclass. To do this, Java uses the "final" keyword, and C++ uses the "const" keyword. Preventing method overriding can be beneficial if a particular function should always be unchanged throughout an inheritance tree.

In general, simple methods that get small pieces of data should not need to be overridden. Cases that tend to benefit most from overriding are when a subclass aims to add functionality to a superclass method without creating an entirely new method to do so. Unusual cases in which a method needs to be completely redone for one specific type of object might also benefit from this technique. Whenever a method is overridden, it is important for the programmer to adequately comment both the superclass and subclass methods. Ideally, these comments should clarify what each variant of the method does, as well as how and why they differ.