polymorphism

问题 I am confused with the static binding example below. I reckon that S2.x and S2.y shows static binding as they prints out the fields according to s2 's static type. And S2.foo() makes s2 call the foo method in the super class, as foo is not over ridden in the subclass. However with S2.goo() , isn't it supposed to call the goo() method in the Test1 subclass? Like it's polymorphism? How come it's static binding? It looks like S2.goo() calls the Super Class goo() method and prints out =13 . Many

问题 I’m building a system using domain driven design and EF 4.1. In some of my properties I have logic preventing illegal values to be set and if so throwing an exception. I thought EF, when instantiating my classes, created a new temporary class e.g. MyClass_abc123… inheriting from MyClass that overrides all virtual members to be able to set them with data from the DB. When EF instantiates the class below and try to set the property MyObj the exception is being thrown. Anyone got a clue or a

问题 I really don't understand as it seems to me the basics of type conformance. I have a Creation instruction lists explicit creation type which does not conform to type of target on create {JANITZA_DEVICE} l_device.make_from_file_path (a_file_path) with eiffel studio 19.5 enterprise. SMA_INVERTER_MANAGER_CSV class SMA_INVERTER_MANAGER_CSV inherit SUNSPEC_DEVICE_CSV[SMA_INVERTER_MANAGER_DEVICE] create make SUNSPEC_DEVICE_CSV deferred class SUNSPEC_DEVICE_CSV[G -> SUNSPEC_DEVICE create make_from

问题 I have a library of classes that describe different pieces of connecting hardware such as nails, screws and bolts that we will call the ConnectorLibrary. I am attempting to build a library on top of that one that will handle analyzing the grip capacity of each class in that library that we will call ConnectorGripAnalysisLibrary. For this question we will work with the classes: Screw , Bolt , and Connector . Both Screw and Bolt inherit from Connector (which is an abstract class) and they are

问题 I have a situation where I have an IEnumerable which I need to iterate through and execute some code against each item. This code to be executed is dependent on the actual type of the item, and what I am looking for is a good clean way of doing this without any conditionals, so if the number of derived types I need to handle increases I simply need to write a new handler and not change any of my existing code. To illustrate this I have the example where the 3rd party library contains the

问题 I am quite new to Slim, still trying to learn it and decided to redo an old app I'd made. I am trying to use Eloquent but have quickly gotten lost doing what I wouldn't think is very complicated. The app I had was even too complicated to learn on, so I backtracked to this tutorial here, as this is more or less what I am trying to do, use models extending one other class, to see if I can even get this working: http://www.richardbagshaw.co.uk/laravel-user-types-and-polymorphic-relationships/ It

问题 Why does the System.out.println(b.h + " " + b.getH()); prints the following: Beta 44 <br/> 4 44 (notice this is in the second line) I was expecting it to print something like this: 4 Beta 44 44 (this one is in one line) The reason why I thought it would print this way is because we call b.h first which is 4.Then we call b.getH() which will print Beta 44 44 Here is the code: class Baap{ int h = 4; public int getH(){ System.out.println("Beta " + h); return h; } } class Beta extends Baap{ int h

问题 Reading stackoverflow questions, the general consensus seems to be that overloading is not part of polymorphism. However, my OOP lecture notes state that: "There are four kinds of polymorphism: Parametric, Inclusion, Coercion, and Overloading". In the notes, it refers to overloading with methods with different parameters, and also overloading operators, e.g. + in the sense of ints and floats. Wikipedia also states "Ad hoc polymorphism is supported in many languages using function overloading.

问题 As noted in this answer: high reliance on dynamic_cast is often an indication your design has gone wrong. What I'd like to know is how can I call a custom function in a derived class, for which there is no same-name function in the base class, but do so using a base class pointer and perhaps without dynamic_cast if in fact there is a better way. If this function was a virtual function defined in both, that's easy. But this is a unique function only in the derived class. Perhaps dynamic_cast

问题 In my site (api using laravel 5.6 and laravel passport) I have two types of users (Teachers and Students), in the future there will be more. The teacher and student entities are very different, meaning that if I keep them all in one table, the table will be long and many fields will have a null value. Right now I have one Users table with common fields and two other tables (Teachers and Students) to which I have setup a polymorphic relationship from user. My question is if this is a good