problem about superclass-Collection of common programming errors

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  CodeFish
  java object casting subclass superclass
  Sorry if this has come up before, but I didn’t see another thread about this. But if there is one, please give me the link.Here I have a simple program. When it runs, it prints out ” 6 4 “public static void main(String[] args) {Foo foo = new Foo();foo.t = 6;foo.f = 4;Bar b = new Foo();ArrayList<Bar> list = new ArrayList<Bar>();list.add((Bar) foo);Foo foo2 = (Foo) list.get(0);System.out.println(foo2.t + ” ” + foo2.f); }static class Bar {int t; }static class Foo extends Bar {int f; }Th
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  trashgod
  java reflection enumeration superclass
  public enum A {A(1);private A(int i){}private A(){super(); // compile – error// Cannot invoke super constructor from enum constructor A()}}and here is the hierarchy of enum A extends from abstract java.lang.Enum extends java.lang.ObjectClass c = Class.forName(“/*path*/.A”); System.out.println(c.getSuperclass().getName()); System.out.println(Modifier.toString(c.getSuperclass().getModifiers()).contains(“abstract”)); System.out.println(c.getSuperclass().getSuperclass().getName());
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  knoxxs
  java polymorphism subclass superclass dynamic-binding
  I know for the case of overriding methods Java follows dynamic binding. But if we call a child only method from the parent reference variable, which is referring to child object, we got compilation error. Why java follow this design (i.e. why no dynamic binding in second case)?class A{public void sayHi(){ “Hi from A”; } }class B extends A{public void sayHi(){ “Hi from B”; public void sayGoodBye(){ “Bye from B”; } }main(){A a = new B();//Works because the sayHi() method is declared in A and overr
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  fkkcloud
  objective-c methods subclass superclass derived-class
  I have two classes, Food and Nacho. Food is Nacho’s super class.Food *junk = [[Nacho alloc] init];is valid as long as I call Food’s methods, right?But how come that Food pointer can call one of Nacho’s methods (which is defined as an additional method in the subclass)?fixed , removed ‘NS’ prefix from class name.
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  Ted
  java reflection override superclass
  I have two classes.public class A {public Object method() {…} }public class B extends A {@Overridepublic Object method() {…} }I have an instance of B. How do I call A.method() from b? Basically, the same effect as calling super.method() from B.B b = new B(); Class<?> superclass = b.getClass().getSuperclass(); Method method = superclass.getMethod(“method”, ArrayUtils.EMPTY_CLASS_ARRAY); Object value = method.invoke(obj, ArrayUtils.EMPTY_OBJECT_ARRAY);But the above code will still invo
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  user2605421
  java subclass superclass
  i’m new with java and have 2 questions about the following code:class Animal { } class Dog extends Animal { } class Cat extends Animal { } class Rat extends Animal { }class Main {List<Animal> animals = new ArrayList<Animal>();public void main(String[] args) {animals.add(new Dog());animals.add(new Rat());animals.add(new Dog());animals.add(new Cat());animals.add(new Rat());animals.add(new Cat());List<Animal> cats = getCertainAnimals( /*some parameter specifying that i want only t
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  Buhake Sindi
  java casting reference subclass superclass
  Suppose I have a superclass Item and a subclass MovingItem.If I create an array of items and then try to cast one of the already created items into a MovingItem and store it in to a vector, does it mean I use a reference or I create a new object, for instance.Item[] itms = new Item[2]; itms[0] = new Item(); itms[1] = new Item();Vector<MovingItem> movingItms = new Vector<MovingItem>(); movingItms.add((MovingItem) itms[0]);What happens when I cast the object of type Itm found in array
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  Matt Huggins
  java class subclass super superclass
  Let’s say I have a base class named Entity. In that class, I have a static method to retrieve the class name:class Entity {public static String getClass() {return Entity.class.getClass();} }Now I have another class extend that.class User extends Entity { }I want to get the class name of User:System.out.println(User.getClass());My goal is to see “com.packagename.User” output to the console, but instead I’m going to end up with “com.packagename.Entity” since the Entity class is being referenced d
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  Anatoly Anatoly
  iphone ios interface superclass conditional-compilation
  I need a way to conditionally define the superclass of a class based on a value in NSUserDefaults.I know one can define different interfaces based on #ifdef directive. I wonder if the same can be achieved with #if directive? If not, is there some other way to achieve my goal?Thank you!
• 
  Isaac
  objective-c override subclass superclass
  Is it possible to override a method in a subclass in such a way that when the superclass calls the method, those calls still go to the original method, but all other (external) calls to the method go to the overridden version?Background: If I subclass a UITextField and override the getter for delegate, the built-in behavior of UITextField that relies on the delegate appears to be using the backing ivar to access the delegate (and not touching the overridden getter); however, if I try the same th
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  supergiox
  java override subclass superclass extends
  My app has a structure similar to this:class Father{ a(){ … }b(){a();} }class Son extends Father{ a(){ ….. }} //overrideb() is not overrided. When I create an instance of Son and I call b(), Father’s a() is called, but I would like it executes the Son one (if the object is a Son). Is it possible?
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  Jeremy Sutton
  java object subclass superclass
  I have a super class called PageObject, and then two subclasses called AlphaPage and BetaPage that inherit the PageObject. A function “selectPage()” will return one of these pages, but the specific page to return will only be known at runtime.What should the function’s return object be, then, that will avoid having to cast one of the subclasses to the function call’s return val?
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  Josh Caswell
• 
  Simeon Visser
  python oop python-2.7 superclass
  I have the following classes:class hello(object):def __init__(self):passclass bye(object):def __init__(self):passl = [hello, bye]If I do the following I get an error:>>> class bigclass(*l):File “<stdin>”, line 1class bigclass(*l):^ SyntaxError: invalid syntaxIs there another way to do this automatically at runtime?I am using Python 2.7.
• 
  groovehunter
  python inheritance superclass
  in my webapp I made two different sessionhandler classes inheriting from a class called SessionHandlerNow I’d like to initiate the appropriate handler (dependent on a cookie value.)Background: My SessionHandler should be the base class of the Controller as it needs to call a Controller backend method otherwise i would assign the handler object to a ctrl member Is there a way to set the superclass at runtime?Or other way to solve that? Hope you got what i meant!
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  comeback
  java swing constructor subclass superclass
  can somebody help me please properly extend my method USBtoUSART in Java? I managed to extend it, but I have problem, to create a new instance of subclass.public class USBtoUSART extends DesktopApplication1View implements SerialPortEventListener{public USBtoUSART(SingleFrameApplication app){super(app); } }public class DesktopApplication1View extends FrameView {SingleFrameApplication ap;USBtoUSART serial = new USBtoUSART(ap);public DesktopApplication1View(SingleFrameApplication app) { sup
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  Pradeep Reddy Kypa
  objective-c ios superclass
  What happens when [super loadView] or [super viewDidLoad] is written? I tried to remove the code but the stack overflows and goes into infinite loop. Can someone please explain why is this required?
• 
  Duncan
  java sockets constructor superclass
  Could you tell me if there is something wrong in this call to the upper class constructor? Every time I try to create a new object with this constructor the application just crashes, I have checked and the parameters that I send are correct, but still crashing…package com.example.bulbcontrol2; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.io.PrintWriter; import java.net.InetAddress; import java.net.Socket;public class ConnectionTool ex
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  Leigh
  java android pdf jar superclass
  I am integrating a Jar file into a test project, to accomplish PDF file reading. This is the library I am trying to integrate:https://github.com/jblough/Android-Pdf-Viewer-LibraryI need to add a jar file and derive the activity from there. Firstly let me say, i have not worked with integrating .jar files, so I might have done something wrong at the “deriving the activity”. Though by now I think I have tried all possible ways of getting this to work.I have a made a new file – PdfReader:package ne
• 
  R G
  ruby-on-rails ruby inheritance methods superclass
  I would like to factor a bunch of common code from subclasses into a superclass method. The superclass method must refer to a nonexistent (in the superclass) method that will be defined in the subclasses. But I can’t get this to work.This is one try out of many multiple variations I have tried:class Superclassdef chunk_of_code# <code…>nonexistant_superclass_method_defined_in_subclass params# <more code…>end endclass Subclass < Superclassdef nonexistant_superclass_method_defi
• 
  Engineer
  actionscript-3 inheritance static-methods superclass private-methods
  I am writing class that extends adobe air PNGEncoder,I want to use the writeChunk method, but it seems to be private static and i cant seems to use it with my code But it gives the error as belowERROR :Description Resource Path Location Type1061: Call to a possibly undefined method writeChunk through a reference with static type com.adobe.images:PNGEncoder. pngMethods.as /FOTO_WITH_AS3_1/src/xmp line 121 Flex ProblemMy classpublic class pngMethods extends PNGEncoder {public fun
• 
  SOaddict
  java inheritance abstract-class superclass
  As Super Class objects cannot be instantiated in the main function abstract keyword is specified before the class name.But what difference does it make if an abstract keyword is used before the SuperClass over-riding method or not used. Can someone explain it please?Here is the below example.Please check the commented part.abstract class Figure {int dim1;int dim2;Figure(){dim1=-1;dim2=-1;}Figure(int p,int q){dim1=p;dim2=q;}abstract void Area() //This line is working without abstract for me.{Syst
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  user1203585
  javascript inheritance canvas subclass superclass
  Possible Duplicate:set attribute with javascript super method I am trying to create a simple game in HTML5 for fun. I have an Entity class that is supposed to be the superclass of the Player class.function Entity(x, y) {this.x = x;this.y = y;this.tick = function() {//Do generic stuff} }function Player(x, y) {this.parent.constructor.call(this, x, y);this.tick = function() {//Do player-specific stuffthis.parent.tick.call(this);} }Player.prototype = new Entity(); Player.prototype.constructor = Pla
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  shaunhusain
  actionscript-3 variables subclass superclass
  I am creating two classes which define the general structure of objects, and many subclasses which are variations of the parents. The variables have the type declaration in the superclasses, and the value declaration in the subclasses. However:[Body_Part_Armor.as]package {import flash.display.*;public class Body_Part_Armor extends MovieClip{var agility_malus;var hp_total;var defense;var armor_extra_height;var armor_extra_width; var hp_left;public function Body_Part_Armor(){hp_left = hp_total;}
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  downer
  java interface subclass superclass
  I’m working on a problem where there are several implementations of Foo, accompanied by several FooBuilder’s. While Foo’s share several common variables that need to be set, they also have distinct variables that require their respective FooBuilder to implement some specific functionality. For succinctness, I’d like to have the FooBuilder’s setters to use method chaining, like: public abstract class FooBuilder {…public FooBuilder setA(int A) {this.A = A;return this;}… }andpublic class FooImp
• 
  JQ.
  c++ multiple-inheritance superclass this-pointer
  context 1: class D : public B1, public B2{};context 2: B2 takes B1 to initialize: B2( B1 * ) //B2’s constructormy question is in D’s initialization list:D::D() : B1(), B2( ? )… What should be in ?I don’t want to put ” (B1*)this ” in the ? place, because it’s no good to use “this” in initialization list. And since B1 part has been initialized, it makes sense to use it.What should I do ?
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  Sophia Ali
  java subclass superclass minesweeper
  I am writing a Minesweeper program, I am trying to write the code for which it will show how many mines are in adjacent grids, however I am getting an error saying a class is expected, I am not sure why. I was under the assumption because both methods are in the MSgrid method it is ok. I have commented the line that is erroring as ERROR HERE. here is my code:/*** Represents a single square in Minesweeper.* * @author Sophia Ali* June 17, 2012*/ public class MineSquare {// Fields:/*** initialize
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  Z i i t o x
  java constructor superclass
  I’m trying to implement the constructor of a class that has more parameters than the parent class, the only one in common is the title. When I try to implement the constructor in the Book class, it shows me an error “Implicit super constructor Item() is undefined”.public class Book extends Item {private String author = “”; private String ISBN = “”; private String publisher = “”;public Book(String theTitle, String theAuthor, String theIsbn, String thePublisher){}}Parent class constructor;public a
• 
  Ben Davis
  header include cmake superclass
  I’ve downloaded a toolkit (namely IRTK from Imperial college) and I have compiled and installed it using CMake.As part of the installation it has copied all of the relevant header files into /usr/local/includeI want to use classes from this toolkit so I include a relevant header file from /usr/local/include, for example irtkFileVTKToImage.h, however this class inherits from a superclass, irtkFileToImage and the include of the superclass occurs in irtkFileVTKToImage.cc not in irtkFileVTKToImage.h
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  Isuru
  java list subclass superclass invariants
  I have following classespublic class Animalpublic class Dog extends Animalpublic class Cat extends AnimalAnd for the testing I have a driver class.public class Driver {public static void main(String[] args){List<? extends Animal> animalList = Arrays.<Dog>asList(new Dog(), new Dog(), new Dog());animalList.add(new Dog()) // Compilation error } }By default list are invariant type containers. For example say we have List<Object> objectList, ArrayList<String>

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