constructor | 易学教程

C# constructor chaining? (How to do it?)

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问题 I know that this is supposedly a super simple question, but I've been struggling with the concept for some time now. My question is, how do you chain constructors in c#? I'm in my first OOP class, so I'm just learning. I don't understand how constructor chaining works or how to implement it, or even why it's better than just doing constructors without chaining. I would appreciate some examples with an explanation. So how do how chain them? I know with two it goes: public SomeClass this: {0}

C# constructor chaining? (How to do it?)

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JavaScript判断变量类型：typeof函数与constructor属性异同

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【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> 有时你可能需要对变量进行类型检查，或者判断变量是否已定义。有两种方法可以使用：typeof函数与constructor属性。 typeof函数的用法可能不用我多说，大家都知道怎么用。而constructor属性大家可能就陌生点。在《精通JavaScript》这本书中有提到construct的用法，但我用自己的几个浏览器（IE7.0 / Firefox1.9 / Opera9.50）测试的结果却和书上说的不一样。但是仍然是有办法通过constructor属性来检查变量类型的。这里先补充一下，为什么明明有typeof函数可以很方便地用来检测类型，还要用constructor呢？因为typeof会把所有的数组类型以及用户自定义类型判断为object，从而无法知道更确切的信息。而constructor却可以解决这个问题。 ok，明白了我们为什么要用constructor，现在让我带大家一步步认识一下typeof和constructor用法之间的差异吧～首先我们运行一下下面这段代码： var i; alert(typeof(i)); alert(i.constructor); 这3行代码告诉你什么情况下可以用constructor。你可以看到第2行返回了字符串'undefined'，而第三行则发生了错误

Patterns: Be independent of different subclasses by passing an Object array to the constructor

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问题 Let's say I load a whole lot of entities from a file. Most of these entities (Not all of them) are of a different class type, and thus may (Or may not) have a different constructor. However, all of them share one superclass: Entity.class How bad/good is it to let the superclass have one constructor public Entity(Object[] args); , so that the arguments will simply also be loaded from file and passed to the constructor, where the constructor then sorts out what exactly to do with that array?

How can I complete my constructor?

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问题 I have this code: override fun onCreateOptionsMenu(menu: Menu): Boolean { menuInflater.inflate(R.menu.menu_search, menu) val searchItem = menu.findItem(R.id.action_search) val searchView = MenuItemCompat.getActionView(searchItem) as SearchView //*** setOnQueryTextFocusChangeListener *** searchView.setOnQueryTextFocusChangeListener(object : View.OnFocusChangeListener() { override fun onFocusChange(v: View, hasFocus: Boolean) { } }) searchView.setOnQueryTextListener(object : SearchView

Changing Object initializer/constructor depending on method input

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问题 So I am trying to avoid using duplicate code. At the moment I have several lists which contain Strings; one list is called "images" and the other "videos" etc. These lists contain the properties of the content and they are in a linked list because that information was read from a text file. I am trying to go through these lists and create image/video objects to place in another object (later on). At the moment I have a method private void loadContent(List<String> contentType) inside of it how

LNK2001 in “How can I make a WNDPROC or DLGPROC a member of my C++ class?”

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问题 VS10: MCBS: Hi there, In the light of this discussion encountered a problem attempting a Hello World implementation of Raymond Chen's method in How can I make a WNDPROC or DLGPROC a member of my C++ class? using Pudeyev's code for "Hello World": error LNK2001: unresolved external symbol "private: long __thiscall BaseWnd::WndProc(struct HWND__ *,unsigned int,unsigned int,long)" (?WndProc@BaseWnd@@AAEJPAUHWND__@@IIJ@Z) The code is as follows: // ...Written by Oleg Pudeyev, (c) 2003 #include

Class Inheritance in Java

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问题 I've been working on a basic class inheritance exercise, and even though I think I've got the jist of it, my program isn't working the way it should. I'm getting compile errors and haven't been able to figure out why- it'd be great if you all could help me out here. So to start off, there are three files 1. Person.java -base class 2. Student.java -a derived class of Person.java 3. Family.java -not quite sure, I think it's its own base class Person.java has two instance variables, String name

Default constructor with empty brackets

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问题 Is there any good reason that an empty set of round brackets (parentheses) isn't valid for calling the default constructor in C++? MyObject object; // ok - default ctor MyObject object(blah); // ok MyObject object(); // error I seem to type "()" automatically everytime. Is there a good reason this isn't allowed? 回答1: Most vexing parse This is related to what is known as "C++'s most vexing parse". Basically, anything that can be interpreted by the compiler as a function declaration will be

c++ Child class Unable to initialize Base class's member variable?

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问题 So this question adds to my previous question about initializing member vector in an initialization list.. Here are my base & derived class definitions... class Base { public: std::vector<int> m_Vector; } class Derived : public Base { Derived() : m_Vector {1, 2, 3} {} // ERROR when referring to m_Vector } When trying to initialize Derived's m_Vector.. I get an error in Visual Studio saying that "m_Vector" is not a nonstatic data member or base class of class "Derived" Why can't derived class