Use of super()

In general, when the subclass has its own instance variables, its constructor must first construct an object of the superclass (using super()) and then construct its own instance variables.

Note:

• What happens if we forget to insert super()? Then the constructor with no arguments of the superclass is called automatically (obviously, if the constructor with no arguments is not defined for the superclass, then a compilation error is signaled).
• What happens if we forget to define constructors for the subclass? Then a constructor with no arguments is automatically defined; such a constructor calls the constructor with no arguments of the superclass and initializes the proper (non inherited) instance variables of the subclass to the default values.
• In this course, we will never make use of these automatic definitions. Instead, we will always explicitly define the constructors of a subclass in such a way that in their first statement they call super().