I tend to prefer the use of @Override in this case, so that the method gets flagged in the subclasses if the superclass changes (either removing the method altogether, or changing its signature, etc.). The only real difference is that without the annotation, if the method in the superclass/interface is changed or removed, the implementation … Read more
Use an abstract property when you have no default implementation and when derived classes must implement it. Use a virtual property when you have an implementation in the base class but want to allow overriding. Use the override keyword to override a member. Mark the member as sealed override if it should not be overridden … Read more
Virtual and abstract are almost the same. A virtual method has an implementation in the base class that can optionally be overridden, while an abstract method hasn’t and must be overridden in a child class. Otherwise they are the same. Choosing between them depends on the situation. If you got a base implementation, you use … Read more
Define a constructor in the abstract class which sets the field so that the concrete implementations are per the specification required to call/override the constructor. E.g. public abstract class AbstractTable { protected String name; public AbstractTable(String name) { this.name = name; } } When you extend AbstractTable, the class won’t compile until you add a … Read more
This may be a bit of a ‘hack’, but does the job with very little effort, but just with a different error message if the constant is not declared in the child class. A self-referential constant declaration is syntactically correct and parses without problem, only throwing an error if that declaration is actually executed at … Read more
You can’t force a particular signature of constructor in your subclass – but you can force it to go through a constructor in your abstract class taking two integers. Subclasses could call that constructor from a parameterless constructor, passing in constants, for example. That’s the closest you can come though. Moreover, as you say, you … Read more
The difference is that all subclasses of a sealed class (whether it’s abstract or not) must be in the same file as the sealed class.
The reason you would use an abstract state is to keep your definition dry when you have a part of your url non-navigable. For example, say that you had a url scheme like the following: /home/index /home/contact However, for whatever reason in your design, this url was invalid (i.e. no purpose for a page): /home … Read more
From the same page you linked to: The interface Comparator is functional because although it declares two abstract methods, one of these—equals— has a signature corresponding to a public method in Object. Interfaces always declare abstract methods corresponding to the public methods of Object, but they usually do so implicitly. Whether implicitly or explicitly declared, … Read more
You’re correct when you say that a class that has a pure virtual function is abstract and can’t be instantiated. But you’re wrong when you say that it can’t have a constructor. Indeed, as your example show, an abstract class can have private members, that may be used by member functions of this class. And … Read more