subclassing

问题 I noticed this is common. For example DefaultListCellRenderer, DefaultTableCellRenderer, and DefaultTreeCellRenderer all use it. Also a lot of the custom cell renderers I see online use this as well. I want to use a custom TableCellRenderer in my code, but I'm confused about whether I really need to subclass JLabel. What's the benefit of subclassing JLabel? 回答1: The API for the DefaultTableCellRenderer states: The table class defines a single cell renderer and uses it as a as a rubber-stamp

问题 When subclassing in objective-c, how can I forward a call to the superclass in the case of a variadic method. By what should I replace the ??? below to send all the objects I got? - (void) appendObjects:(id) firstObject, ... { [super appendObjects: ???]; } 回答1: You can't. To safely pass all the variadic arguments, you need a method to accept a va_list . In super, -(void)appendObjectsWithArguments:(va_list)vl { ... } -(void)appendObject:(id)firstObject, ... va_list vl; va_start(vl, firstObject

问题 (Followup question to this one) I'm writing a program that uses a library, whose header file defines enum foo : unsigned { first_foo, second_foo }; Now, I want to add some aliases to foo values. If I were in control of the library's source, I would write: enum foo : unsigned { first_foo, second_foo, best_foo = first_foo, worst_foo = second_foo, oldest_foo = first_foo, newest_foo = second_foo; }; ... but I don't control the source. So, I would have liked to write: enum bar : foo { best_foo =

问题 So, I have two instances of a class Person and I am trying to do some comparisons. sun is one of several attributes of each instance is defined by two randomly generated numbers. I have the following questions... Is creating a subclass like Match the right way to go about setting up this comparison? And I want an overall "score" compiled at the end of this comparison, can I do that without the for-loop? Person1 = Person("Person1") Person2 = Person("Person2") class Match(Person): overall = 0

问题 Why does the total count of methods reduce, from 81 to 46 while instantiating an object from 'Class' class-objects? Here's the code I'm running: class Automobile def wheels(wheel) puts "#{wheel}" end end class Car < Automobile def gears puts "Automatic Transmission" end end limo = Car.new benz = Automobile.new puts Automobile.methods.count puts Car.methods.count puts benz.methods.count puts limo.methods.count I guess subclass is not inheriting certain methods, I thought they are class methods

问题 I would like to roughly monitor the progress of a file upload. I know that I can override the MultipartEntity and make the writeTo(OutputStream out) method write to a FilterOutputStream class that I created to wrap the default InputStream. For full details on how I did that, see my answer here. However, upon closer inspection this counts every byte sent twice! I went to the documentation to see what was up. Looks like FilterOutputStream's write(byte[], int, int) method simply calls the

问题 I have an generic abstract class, BString , which expects one of its types to implement Comparable . Another class, NGram extends BString , passing String as the comparable type. A final class, BinarySearchTree expects keys which extend Comparable . Why am I unable to create a BinarySearchTree with NGram as the key type? Does the implements Comparable declaration for BString strictly hold for BString and none of its descendants? I have included the class declarations below, and note that

问题 I want to subclass NSURLSession class, but I have problem with initialisation. Basically I override the constructor and initialising the constant authUrl there then calling the parent init method. class NSURLAuthSession: NSURLSession { let authUrl:NSURL; //Error: Initializer does not override a designated initializer from its superclass override init(configuration: NSURLSessionConfiguration, delegate: NSURLSessionDelegate?, delegateQueue queue: NSOperationQueue?){ self.authUrl = NSURL

问题 As a newbie in Scala, I have stumbled on this seemingly easy point of SubClassing and Overriding methods. I have specialized a Set thus: class SpecializedSet [T](s:Int, b: Boolean) (implicit ordering: Ordering [T]) extends TreeSet [T] { override def + (t: T): SpecializedSet [T] = { if (this.isEmpty) { s = s + 1 // I want to add an element to the Set super.+ (t) } .... } At the site of using this class, I do: class Driver { var e = new SpecializedSet [MyEarlierDefinedType](3,false); ...... val

问题 I have a class that subclasses QObject. Everyting works fine but when I run mypy on it I get the error: "error: Class cannot subclass 'QObject' (has type 'Any')" At the moment I am totally stuck. I Have been reading the mypy docs but couldn't find where the error was. Here the code: from PyQt5.QtCore import QObject class ServiceLocator(QObject): def __init__(self) -> None: super().__init__() ... Cheers. 回答1: This error occurs when mypy doesn't have type information for a class (in your case