overriding | 易学教程

Java inheritance (method overriding and overloading)

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问题 Besides that Java inheritance is a fundamental feature of the language, I have some questions. Here is the source for my testing example: class MyClass{ public void say(String t){ System.out.println("Hello MyClass "+t); } public void print(MyClass t){ System.out.println("MyClass is printed"); } public void anotherPrint(int i){ System.out.println("MyClass is printed again"); } } class MyClass2 extends MyClass{ public void say(String t){ System.out.println("Hello MyClass2 "+t); } public void

java non-static to static method — hiding or overriding

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is re-defining a non-static method in a subclass with the same everything but as static overriding or hiding it ? http://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html says hiding. but when i declare the superclass method as final, i get an override error. superclass declaration is final static void display() { ... } subclass: void display() { ... } gives override error. Is re-defining a non-static method in a subclass with the same everything but as static overriding or hiding it? It's neither, because doing so triggers a compilation error , rendering your program invalid. class A

Objective C subclass that overrides a method in the superclass

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问题 In Objective C, if you are subclassing something, and are planning to override a method on the superclass, should you re-declare the superclass method in your subclass @interface? For example, if you are subclassing UIViewController (e.g. MyViewController), and you are planning to override "viewDidLoad" should you include that method in your MyViewController @interface declaration, or just implement it in MyViewController.m? In examples I've come across, I've seen it done both ways (re

how can i override malloc(), calloc(), free() etc under OS X?

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问题 Assuming the latest XCode and GCC, what is the proper way to override the memory allocation functions (I guess operator new/delete as well). The debugging memory allocators are too slow for a game, I just need some basic stats I can do myself with minimal impact. I know its easy in Linux due to the hooks, and this was trivial under codewarrior ten years ago when I wrote HeapManager. Sadly smartheap no longer has a mac version. 回答1: I would use library preloading for this task, because it does

Swift property override not working

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问题 When I try to override a property I get an error "can not override mutable property with read-only property" I have provided get and set in the super class. class Card { var contents:String { get { return self.contents } set { self.contents = newValue } } init() { self.contents = "" } } Here is my Subclass where I am trying to override the "contents" property. class PlayingCard: Card { override var contents:String { //<-- this is where I get the build error get { var rankStrings:Array<String>

How to override external css?

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I have an external css file which applies 35px padding to my content div. All my html pages are loaded inside that div but for one of them I want to use 0 padding-right. I tried inline css, applying it directly on the body of that page and also using !important but nothing worked. What I am I doing wrong? index.html: <div id="content"><?php include "page.html"?></div> main.css: #content{ margin-top: 303px; padding: 35px; z-index:1; } page.html: <body style="padding:0px;"> To override a css setting you must use the keyword important. <body style="padding:0px ! important;"> CSS reads top-down,

Why can't I use builtin for classes that overload subsref?

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问题 I would like to overload only one type of subsref calls (the '()' type) for a particular class and leave any other calls to Matlab's built in subsref -- specifically, I want Matlab to handle property/method access via the '.' type. But, it seems like Matlab's 'builtin' function doesn't work when subsref is overloaded in a class. Consider this class: classdef TestBuiltIn properties testprop = 'This is the built in method'; end methods function v = subsref(this, s) disp('This is the overloaded

.NET events - blocking subscribers from subscribing on an event

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Let's say I have a "Processor" interface exposing an event - OnProcess. Usually the implementors do the processing. Thus I can safely subscribe on this event and be sure it will be fired. But one processor doesn't do processing - thus I want to prevent subscribers to subscibe on it. Can I do that? In other words in the code below I want the last line to throw an exception: var emptyProcessor = new EmptyProcessor(); emptyProcessor.OnProcess += event_handler; // This line should throw an exception. class EmptyProcessor : IProcessor { [Obsolete("EmptyProcessor.OnProcess should not be directly

Override designated initializer of superclass

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I am reading a book which has a guideline: "If a class declares a designated initializer that is different from its superclass, the superclass’s designated initializer must be overridden to call the new designated initializer" As I understand this guideline in other words is that, if I am subclassing my class form its superclass, and my subclass has a designated initializer which is different from des. initializer of its superclass, then in my subclass I must override the designated initializer of my superclass and inside it call the designated initializer of my subclass. Is this true? Do we

How to override a field in the parent class

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I have parent and child classes in Django model. And I want to fill a field in parent class when initialize child class. Or override this field in child class. class Parent(models.Model): type = models.CharField() class Child(Parent): type = models.CharField() //Doesn't work Also trying override init method, but it doesn't work too. How can I accomplish this? In normal Python class inheritance, it is permissible for a child class to override any attribute from the parent class. In Django, this is not permitted for attributes that are Field instances (at least, not at the moment). If a base