inheritance

问题 The Java language specification specifies that In the Java programming language arrays are objects (§4.3.1), are dynamically created, and may be assigned to variables of type Object (§4.3.2). All methods of class Object may be invoked on an array. So, considering arrays are objects — why did the Java designers make the decision not to allow inherit and override from it, for example, toString() or equals() ? The current syntax wouldn't allow creating anonymous classes with an array as the base

问题 I'm working in a web app framework, and part of it consists of a number of services, all implemented as singletons. They all extend a Service class, where the singleton behaviour is implemented, looking something like this: class Service { protected static $instance; public function Service() { if (isset(self::$instance)) { throw new Exception('Please use Service::getInstance.'); } } public static function &getInstance() { if (empty(self::$instance)) { self::$instance = new self(); } return

问题 I have an internationalized project with many modules. Each module has its own set of bundles: - database-module + com_naugler_project_database.properties + com_naugler_project_database_fr.properties - mapping-module + com_naugler_project_mapping.properties + com_naugler_project_mapping_fr.properties However, many of the internationalized terms are redundant (such as 'OK' or 'Cancel') and I would like have these terms in one place for easier maintenance and development. I found this helpful

问题 I've come to a point in a Go project of mine where I'd like to create multiple subclasses of a base class, and be able to operate on instances of the subclasses through a base class/interface variable (I'm using the word "class" even though the concept doesn't really exist in Go). Here's what it might look like in C++ just to show what I mean: #include <iostream> using namespace std; class Base { public: int x,y; virtual void DoStuff() {}; }; class Thing : public Base { public: void DoStuff()

问题 This one has me stumped. What I'm trying to do is get a reference variable in a wrapper class to point to a struct object in the class it wraps so that any setting of variables in the struct from other classes that use the wrapper class, actually are set in the wrapped class not the wrappper class. To do this I tried to simply create a reference in the wrap class to the struct in the wrapped class like class CClassWrap { CClass::plot_type& PlotArgs; } and then init PlotArgs CClassWrap:

问题 How can I draw on QWidget(element on my form)? I read many tutorials but none of them covers what I really have to do(draw some Rect on QWidget) . I made a class MyFigure which inherits from QWidget, and at even paint wrote some code to draw a rectangle. Then, in my Form Create I create MyFigure object, and just show it. IT DOESN"T WORK!!! 回答1: QGraphicsView and QGraphicsScene are good for painting, but if you want to draw on QWidget you need to reimplement paintEvent: #include <QWidget>

问题 Closed . This question is opinion-based. It is not currently accepting answers. Want to improve this question? Update the question so it can be answered with facts and citations by editing this post. Closed 5 years ago . I'm referring to MDN's article on JavaScript's 'future reserved words' (for use in the new strict mode) - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Lexical_grammar#Future_reserved_keywords . All the reserved words indicate that JavaScript will possibly

问题 I found an example of how to do single table inheritance using Class mappings. http://docs.sqlalchemy.org/en/latest/orm/inheritance.html#single-table-inheritance But for the life of me, I cannot find an example of how to do this with classic mapper so that I can keep my classes and persistent mappings separate. How do I convert this example into classic mapping? I am clear on creating the tables, just not sure how to actually structure the mapper. In the example, there are the following types

问题 i have the following: class base { public void f(); ... } void base::f() { static bool indicator=false; ..... if(!indicator) { ... indicator=true; } } class D:public base { ... } in my main() i have: main() { // first instance of D base *d1 = new D(); d1->f(); .... // 2nd instance of D base *d2 = new D(); d2->f(); } i find that the first time i instantiate D and call d1->f() the static variable is set to false. but the 2nd time i call d2->f() the code does not even hit the line "static bool

问题 I am look into the book "Java Concurrency in Practice" and found really hard to believe below quoted statement (But unfortunately it make sense). http://www.informit.com/store/java-concurrency-in-practice-9780321349606 Just wanted to get clear about this 100% public class Holder { private int n; public Holder(int n) { this.n = n; } public void assertSanity() { if (n != n) throw new AssertionError("This statement is false."); } } While it may seem that field values set in a constructor are the