What does “abstract” means?

That this Class cannot have objects and can also have abstract methods that are empty and must be overridden in the subclasses to make them operational.


Subclass constructor

The subclass construct method first must build the super-class (or if there’s more than one,  execute them from the highest level, one by one) and finally build himself.

public Class(){ super(); this(); }

What is overriding?

You can define different a method in a sub-class identical to one from the super-class. Then the object will execute the method according to his class . If doesn’t exits there, he will execute it from the super-class.

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