The only way around this is to declare your class as abstract and leave it to a subclass to implement the missing methods. But ultimately, someone in the chain has to implement it to meet the interface contract. If you truly do not need a particular method, you can implement it and then either return … Read more
The problem is that you’re trying to use the T from SqlReaderBase as the type argument for MapperBase – but you don’t have any constraints on that T. Try changing your SqlReaderBase declaration to this: public abstract class SqlReaderBase<T> : ConnectionProvider where T : new() Here’s a shorter example which demonstrates the same issue: class … Read more
Mixins is all about how a class does what it does, it’s inheriting and sharing concrete implementation. Interfaces is all about what a class is, it is the abstract signature and promises that the class must satisfy. It’s a type. Take a class that is implemented as class MyList<T> extends Something with ListMixin<T> …. You … Read more
From Java How to Program about abstract classes: Because they’re used only as superclasses in inheritance hierarchies, we refer to them as abstract superclasses. These classes cannot be used to instantiate objects, because abstract classes are incomplete. Subclasses must declare the “missing pieces” to become “concrete” classes, from which you can instantiate objects. Otherwise, these … Read more
If you have no concrete implementations of the class and the methods aren’t static whats the point of testing them? If you have a concrete class then you’ll be testing those methods as part of the concrete class’s public API. I know what you are thinking “I don’t want to test these methods over and … Read more
Abstract Class An abstract class is a class that is not designed to be instantiated. Abstract classes can have no implementation, some implementation, or all implementation. Abstract classes are designed to allow its subclasses share a common (default) implementation. A (pseudocoded) example of an abstract class would be something like this abstract class Shape { … Read more
A class can only extend one superclass, and thus, only one abstract class. If you want to compose several classes the Scala way is to use mixin class composition: you combine an (optional) superclass, your own member definitions and one or more traits. A trait is restricted in comparison to classes in that it cannot … Read more
You’re using Arrays.asList() to create the lists in the Map here: itemStockMap.put(item.getInfo(), Arrays.asList(item.getStock())); This method returns a non-resizable List backed by the array. From that method’s documentation: Returns a fixed-size list backed by the specified array. (Changes to the returned list “write through” to the array.) In order to use a resizable List (and actually … Read more
The implements keyword treats the A class as an interface, that means C has to implement all the methods defined in A, no matter if they have an implementation or not in A. Also there are no calls to super methods in C. extends behaves more like what you’d expect from the keyword. You have … Read more
You can’t instantiate abstract classes, thus a vector of abstract classes can’t work. You can however use a vector of pointers to abstract classes: std::vector<IFunnyInterface*> ifVec; This also allows you to actually use polymorphic behaviour – even if the class wasn’t abstract, storing by value would lead to the problem of object slicing.