Polymorphism is one of the tenets of Object Oriented Programming (OOP). It is the practice of designing objects to share behaviors and to be able to override shared behaviors with specific ones. Polymorphism takes advantage of inheritance in order to make this happen. In OOP everything is considered to be modeled as an object. This … Read more
You can try using a “catchpoint” (catch throw) to stop the debugger at the point where the exception is generated. The following excerpt From the gdb manual describes the catchpoint feature. 5.1.3 Setting catchpoints You can use catchpoints to cause the debugger to stop for certain kinds of program events, such as C++ exceptions or … Read more
As promised, I’m putting an example for how to use annotations to serialize/deserialize polymorphic objects, I based this example in the Animal class from the tutorial you were reading. First of all your Animal class with the Json Annotations for the subclasses. import com.fasterxml.jackson.annotation.JsonIgnoreProperties; import com.fasterxml.jackson.annotation.JsonSubTypes; import com.fasterxml.jackson.annotation.JsonTypeInfo; @JsonIgnoreProperties(ignoreUnknown = true) @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include … Read more
It’s hard to understand higher-rank polymorphism unless you study System F directly, because Haskell is designed to hide the details of that from you in the interest of simplicity. But basically, the rough idea is that polymorphic types don’t really have the a -> b form that they do in Haskell; in reality, they look … Read more
They can result if you try to make a virtual function call from a constructor or destructor. Since you can’t make a virtual function call from a constructor or destructor (the derived class object hasn’t been constructed or has already been destroyed), it calls the base class version, which in the case of a pure … Read more
============= UPDATE: I used this answer as the basis for this blog entry: Why do ref and out parameters not allow type variation? See the blog page for more commentary on this issue. Thanks for the great question. ============= Let’s suppose you have classes Animal, Mammal, Reptile, Giraffe, Turtle and Tiger, with the obvious subclassing … Read more
How are virtual functions implemented at a deep level? From “Virtual Functions in C++”: Whenever a program has a virtual function declared, a v – table is constructed for the class. The v-table consists of addresses to the virtual functions for classes that contain one or more virtual functions. The object of the class containing … Read more
The difference is that, for example, a List<HashMap<String,String>> is a List<? extends Map<String,String>> but not a List<Map<String,String>> So: void withWilds( List<? extends Map<String,String>> foo ){} void noWilds( List<Map<String,String>> foo ){} void main( String[] args ){ List<HashMap<String,String>> myMap; withWilds( myMap ); // Works noWilds( myMap ); // Compiler error } You would think a List of … Read more
GetType() will return the actual, instantiated type. In your case, if you call GetType() on an instance of B, it will return typeof(B), even if the variable in question is declared as a reference to an A. There is no reason for your GetSubType() method.
Understanding of / requirements for polymorphism To understand polymorphism – as the term is used in Computing Science – it helps to start from a simple test for and definition of it. Consider: Type1 x; Type2 y; f(x); f(y); Here, f() is to perform some operation and is being given values x and y as … Read more