February 2, 2021

Forrige forelesning (subklasser og arv) Neste forelesning (arv og interface)

Polymorfi (Polymorphism)

A virtual function or virtual method (also known as polymorphic) is a function or method whose behavior can be overridden within an inheriting class by a function with the same signature to provide the polymorphic behavior.
All the methods in Java are virtual, if they are not declared final.
The overriding method needs to have the exact same signature and name as the super-class method - otherwise the program treats them as two different methods.
@Override annotation is used to explicitly tell the program that the method is being overridden. This is useful for two reasons:
- When compiling, the program will tell you if some of the overriding methods don't match and point to them.
- The code becomes more readable.
If we define an object of a sub-class, but declare it as an object of a super-class, and then try to call the overridden method, the compiler will approve of it and treat it as a super-class method, but the run-time system will perform the sub-class method.
You can use a key-word super.method() to refer to the super-class method within the overriding one.
Super-class variables can also be overridden, but that's a no-no, cuz it reduces the code readability and leads to unpredictable behavior.

Overriding happens when the two methods have the same signature
Overloading happens when the two methods have different signatures (e.g. the name and data type is the same, but the parameters are different).