subclass

问题 I'm trying to assign a sub class object array to its super class. The program compiles successfully, but I' getting an ArrayStoreException . I know that arrays parent and child are references to same array, but shouldn't I be able to access method func at least? class Pclass { Pclass() { System.out.println("constructor : Parent class"); } public void func() { System.out.println("Parent class"); } } class Cclass extends Pclass { Cclass() { System.out.println("Constructor : Child class"); }

问题 Django 1.11. In admin.py I have: class AuditAdmin(DeactivateMixin, admin.ModelAdmin): """all the superclass stuff""" from which I subclass my model's stuff with various custom methods: class SomeModelAdmin(AuditAdmin): list_display = ["filed1", "filed2", "field3"] def get_queryset(self, request): if request.user.is_superuser: #do something extra def inline_add_somemodelattribute1(self, my_object): #how to access user if I don't have request ? So inside inline_add_somemodelattribute1 method I

问题 This question already has an answer here : ES6 Object Destructuring Default Parameters (1 answer) Closed 2 years ago . Context: this is a task in a javascript tutorial. The code is supposed to generate a subclass ExtendedClock of Clock that allows the console to show the current time in a customized interval of time. Class Clock { constructor({ template }) { this._template = template; } _render() { let date = new Date(); let hours = date.getHours(); if (hours < 10) hours = '0' + hours; let

问题 I am a very new, relatively inexperienced Java programmer. The project I am working is just a test of my current skills, and my goal is to write as efficient a program as possible. In essence, I have three classes: A, B, and C. B extends A and C extends B, but I want a Scanner object in C to be used in a switch statement (part of a larger method) in A. The reason I want this is because I do not want to overload the method in A (copy-pasting the same code with different parameters is not ideal

问题 I am writing a php app with subclasses and since I want to have multiple ways to create an object I am doing different factory methods instead of multiple constructors. I have a User with factory methods User::from_id User::from_netid I have several subclasses of User . I was previously calling the parent superconstructor, but when I switched to the factory method that constructor didn't exist. I have Student , a subclass of User . To get it to work, I had to duplicate almost all of my

问题 I am building a multiple screen App with Kivy and I would like to use the ScreenManager to navigate between the multiple screens. I have seen examples and documentation for how to create the screens within a .kv file, but I want to know how to create them within the .py file. Problem: When I create the screen subclasses as shown below, my app window returns a blank screen. Question: What is the correct way to create the Screen subclasses within a .py file? Right now I have two Screen

问题 When using map() from multiprocessing.Pool() on a list of instances from a numpy.ndarray -subclass, the new attributes of the own class are dropped. The following minimal example based on the numpy docs subclassing example reproduces the problem: from multiprocessing import Pool import numpy as np class MyArray(np.ndarray): def __new__(cls, input_array, info=None): obj = np.asarray(input_array).view(cls) obj.info = info return obj def __array_finalize__(self, obj): if obj is None: return self

问题 This is a very basic question about subclasses in java, I still don't get it... Suppose I have a superclass with three fields and with only the default constructor: public class Superclass { public int a; public int b; public int c; } and I want to add a field x. I cannot change Superclass , so I make a subclass: public class Subclass extends Superclass { public int x; public Subclass(Superclass s) { super(); // what to do?? } } I now want to generate a Subclass object from an existing

问题 Is it possible for no override for happen? For example: class A: def __init__(self, name): self.name = name class B(A): def __init__(self, name): A.__init__(self, name) self.name = name + "yes" Is there any way for self.name in class B to be independent from that of Class A's, or is it mandatory to use different names? 回答1: Prefixing a name with two underscores results in name mangling, which seems to be what you want. for example class A: def __init__(self, name): self.__name = name def

问题 Let's have these classes: class A { fun foo(): A = this } class B: A() { fun bar() { ... } } Now I would like Kotlin to detect when I call foo on B , and give me the result typed as B . So that I can write: B().foo().bar() With kotlin 1.4.20, this is not possible - it would need an explicit cast to B after foo() . Perhaps it could be handled by the compiler, if it clearly sees that the function returns this . Or maybe we could hint it explicitly... class A { fun <Self> foo(): Self = this } I