? as a type parameter can only be used in methods. eg: printAll(MyList<? extends Serializable>) I cannot define classes with ? as type parameter. A wildcard (?) isn’t a formal type parameter, but rather can be used as a type argument. In the example you give, ? extends Serializable is given as a type argument … Read more
Before I dig into multi table inheritance I want to lose a few words about single table inheritance. Single table inheritance is the more easy way when it comes to inheritance with db models. You have multiple models bound to the same table and a type column to distinguish between the different model classes. However … Read more
Regarding several other answers, this doesn’t have anything to do with dates being implemented in C per se. The __init__ method does nothing because they are immutable objects, therefore the constructor (__new__) should do all the work. You would see the same behavior subclassing int, str, etc. >>> import datetime >>> class D(datetime.date): def __new__(cls, … Read more
You should probably call dict.__init__(self) when subclassing; in fact, you don’t know what’s happening precisely in dict (since it’s a builtin), and that might vary across versions and implementations. Not calling it may result in improper behaviour, since you can’t know where dict is holding its internal data structures. By the way, you didn’t tell … Read more
No, the private member are not inherited because the scope of a private member is only limited to the class in which it is defined. Only the public and protected member are inherited. From the Java Documentation, Private Members in a Superclass A subclass does not inherit the private members of its parent class. However, … Read more
If you want a custom collection that actually holds the data, subclass dict. This is especially useful if you want to extend the interface (e.g., add methods). None of the built-in methods will call your custom __getitem__ / __setitem__, though. If you need total control over these, create a custom class that implements the collections.MutableMapping … Read more
You have to read the API carefully for this methods. Sometimes you can get confused very easily. It is either: if (B.class.isInstance(view)) API says: Determines if the specified Object (the parameter) is assignment-compatible with the object represented by this Class (The class object you are calling the method at) or: if (B.class.isAssignableFrom(view.getClass())) API says: Determines … Read more
You can use issubclass() like this assert issubclass(suit, Suit).
You never need just super(); That’s what will be there if you don’t specify anything else. You only need to specify the constructor to call if: You want to call a superclass constructor which has parameters You want to chain to another constructor in the same class instead of the superclass constructor You claim that: … Read more
class Base { public: virtual ~Base() {} }; class D1: public Base {}; class D2: public Base {}; int main(int argc,char* argv[]); { D1 d1; D2 d2; Base* x = (argc > 2)?&d1:&d2; if (dynamic_cast<D2*>(x) == nullptr) { std::cout << “NOT A D2” << std::endl; } if (dynamic_cast<D1*>(x) == nullptr) { std::cout << “NOT … Read more