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  • Using java abstract class

    - by user969131
    In my UI project, I have few screens that share the same header style only the text is specific to the screens. What will be a good way to implement this? Have the super class create all the header component and open the components to the sub class, the sub class will access to component's setText method to update the text? or Have abstract method in super class to create the components, sub class will implement these methods to create the component. Hope it make sense..

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  • DIV is picking max-width value as width value for DIV.

    - by Lokesh
    I am facing a problem after applying max-width hack for IE7. In mozilla, width of the div is flexible and adjustable as per the image width in the div. But in IE7 it is taking the max-width as width of DIV. Below is my HTML code: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <link rel="stylesheet" type="text/css" media="all" href="style/food.css" /> <!--[if IE 7]> <link rel="stylesheet" type="text/css" media="screen" href="style/ie7.css" /> <![endif]--> </head> <body> <div class="main_content_inner_ko"> <div class="product_item"> <img src="images/product_icons/BigNTasty.png" alt="Big N&rsquo; Tasty"/><div class="small_title">Big N&rsquo; Tasty</div> <table class="product_information" cellpadding="0" border="0" cellspacing="0"> <tbody> <tr> <td class="red_bold"></td> <td></td> <td class="small_italic">(Daily Value)</td> </tr> <tr> <td class="red_bold">Calories</td> <td>460</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Total Fat</td> <td>24g</td> <td class="small_italic">(37%)</td> </tr> <tr> <td class="red_bold">Carbs</td> <td>37g</td> <td class="small_italic">(12%)</td> </tr> <tr> <td class="red_bold">Protein</td> <td>24g</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Sodium</td> <td>720mg</td> <td class="small_italic">(30%)</td> </tr> <tr> <td colspan="3" class="notes">Note: Values shown are for the default size and/or flavor.</td> </tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_learn_more_and_customize"></a></td></tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_add_to_my_meal_builder"></a></td></tr> </tbody> </table> </div> <div class="product_item"> <img src="images/product_images/x115/chicken/PremCrispyChickenRanchBLT.png" height="115" width="115" alt="Premium Cripsy Chicken Ranch BLT"/><div class="small_title">Premium Cripsy Chicken Ranch BLT</div> <table class="product_information" cellpadding="0" border="0" cellspacing="0"> <tbody> <tr> <td class="red_bold"></td> <td></td> <td class="small_italic">(Daily Value)</td> </tr> <tr> <td class="red_bold">Calories</td> <td>460</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Total Fat</td> <td>24g</td> <td class="small_italic">(37%)</td> </tr> <tr> <td class="red_bold">Carbs</td> <td>37g</td> <td class="small_italic">(12%)</td> </tr> <tr> <td class="red_bold">Protein</td> <td>24g</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Sodium</td> <td>720mg</td> <td class="small_italic">(30%)</td> </tr> <tr> <td colspan="3" class="notes">Note: Values shown are for the default size and/or flavor.</td> </tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_learn_more_and_customize"></a></td></tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_add_to_my_meal_builder"></a></td></tr> </tbody> </table> </div> <div class="product_item"> <img src="images/product_images/x115/sandwiches/FiletOFish.png" height="115" width="99" alt="Filet O Fish"/> <div class="small_title">Filet O Fish</div> <table class="product_information" cellpadding="0" border="0" cellspacing="0"> <tbody> <tr> <td class="red_bold"></td> <td></td> <td class="small_italic">(Daily Value)</td> </tr> <tr> <td class="red_bold">Calories</td> <td>460</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Total Fat</td> <td>24g</td> <td class="small_italic">(37%)</td> </tr> <tr> <td class="red_bold">Carbs</td> <td>37g</td> <td class="small_italic">(12%)</td> </tr> <tr> <td class="red_bold">Protein</td> <td>24g</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Sodium</td> <td>720mg</td> <td class="small_italic">(30%)</td> </tr> <tr> <td colspan="3" class="notes">Note: Values shown are for the default size and/or flavor.</td> </tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_learn_more_and_customize"></a></td></tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_add_to_my_meal_builder"></a></td></tr> </tbody> </table> </div> <div class="product_item"> <img src="images/product_icons/BigNTasty.png" height="115" width="99" alt="Big N&rsquo; Tasty"/> <div class="small_title">Big N&rsquo; Tasty</div> <table class="product_information" cellpadding="0" border="0" cellspacing="0"> <tbody> <tr> <td class="red_bold"></td> <td></td> <td class="small_italic">(Daily Value)</td> </tr> <tr> <td class="red_bold">Calories</td> <td>460</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Total Fat</td> <td>24g</td> <td class="small_italic">(37%)</td> </tr> <tr> <td class="red_bold">Carbs</td> <td>37g</td> <td class="small_italic">(12%)</td> </tr> <tr> <td class="red_bold">Protein</td> <td>24g</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Sodium</td> <td>720mg</td> <td class="small_italic">(30%)</td> </tr> <tr> <td colspan="3" class="notes">Note: Values shown are for the default size and/or flavor.</td> </tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_learn_more_and_customize"></a></td></tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_add_to_my_meal_builder"></a></td></tr> </tbody> </table> </div> <div class="product_item"> <img src="images/product_images/x115/chicken/PremCrispyChickenRanchBLT.png" height="115" width="115" alt="Premium Cripsy Chicken Ranch BLT"/> <div class="small_title">Premium Cripsy Chicken Ranch BLT</div> <table class="product_information" cellpadding="0" border="0" cellspacing="0"> <tbody> <tr> <td class="red_bold"></td> <td></td> <td class="small_italic">(Daily Value)</td> </tr> <tr> <td class="red_bold">Calories</td> <td>460</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Total Fat</td> <td>24g</td> <td class="small_italic">(37%)</td> </tr> <tr> <td class="red_bold">Carbs</td> <td>37g</td> <td class="small_italic">(12%)</td> </tr> <tr> <td class="red_bold">Protein</td> <td>24g</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Sodium</td> <td>720mg</td> <td class="small_italic">(30%)</td> </tr> <tr> <td colspan="3" class="notes">Note: Values shown are for the default size and/or flavor.</td> </tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_learn_more_and_customize"></a></td></tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_add_to_my_meal_builder"></a></td></tr> </tbody> </table> </div> <div class="product_item"> <img src="images/product_images/x115/sandwiches/FiletOFish.png" height="115" width="99" alt="Filet O Fish"/> <div class="small_title">Filet O Fish</div> <table class="product_information" cellpadding="0" border="0" cellspacing="0"> <tbody> <tr> <td class="red_bold"></td> <td></td> <td class="small_italic">(Daily Value)</td> </tr> <tr> <td class="red_bold">Calories</td> <td>460</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Total Fat</td> <td>24g</td> <td class="small_italic">(37%)</td> </tr> <tr> <td class="red_bold">Carbs</td> <td>37g</td> <td class="small_italic">(12%)</td> </tr> <tr> <td class="red_bold">Protein</td> <td>24g</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Sodium</td> <td>720mg</td> <td class="small_italic">(30%)</td> </tr> <tr> <td colspan="3" class="notes">Note: Values shown are for the default size and/or flavor.</td> </tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_learn_more_and_customize"></a></td></tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_add_to_my_meal_builder"></a></td></tr> </tbody> </table> </div> <div class="product_item"> <img src="images/product_icons/BigNTasty.png" height="115" width="99" alt="Big N&rsquo; Tasty"/> <div class="small_title">Big N&rsquo; Tasty</div> <table class="product_information" cellpadding="0" border="0" cellspacing="0"> <tbody> <tr> <td class="red_bold"></td> <td></td> <td class="small_italic">(Daily Value)</td> </tr> <tr> <td class="red_bold">Calories</td> <td>460</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Total Fat</td> <td>24g</td> <td class="small_italic">(37%)</td> </tr> <tr> <td class="red_bold">Carbs</td> <td>37g</td> <td class="small_italic">(12%)</td> </tr> <tr> <td class="red_bold">Protein</td> <td>24g</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Sodium</td> <td>720mg</td> <td class="small_italic">(30%)</td> </tr> <tr> <td colspan="3" class="notes">Note: Values shown are for the default size and/or flavor.</td> </tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_learn_more_and_customize"></a></td></tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_add_to_my_meal_builder"></a></td></tr> </tbody> </table> </div> <div class="product_item"> <img src="images/product_icons/BigNTasty.png" height="115" width="99" alt="Big N&rsquo; Tasty"/> <div class="small_title">Big N&rsquo; Tasty</div> <table class="product_information" cellpadding="0" border="0" cellspacing="0"> <tbody> <tr> <td class="red_bold"></td> <td></td> <td class="small_italic">(Daily Value)</td> </tr> <tr> <td class="red_bold">Calories</td> <td>460</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Total Fat</td> <td>24g</td> <td class="small_italic">(37%)</td> </tr> <tr> <td class="red_bold">Carbs</td> <td>37g</td> <td class="small_italic">(12%)</td> </tr> <tr> <td class="red_bold">Protein</td> <td>24g</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Sodium</td> <td>720mg</td> <td class="small_italic">(30%)</td> </tr> <tr> <td colspan="3" class="notes">Note: Values shown are for the default size and/or flavor.</td> </tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_learn_more_and_customize"></a></td></tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_add_to_my_meal_builder"></a></td></tr> </tbody> </table> </div> <div class="product_item"> <img src="images/product_images/x115/sandwiches/FiletOFish.png" height="115" width="99" alt="Filet O Fish"/> <div class="small_title">Filet O Fish</div> <table class="product_information" cellpadding="0" border="0" cellspacing="0"> <tbody> <tr> <td class="red_bold"></td> <td></td> <td class="small_italic">(Daily Value)</td> </tr> <tr> <td class="red_bold">Calories</td> <td>460</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Total Fat</td> <td>24g</td> <td class="small_italic">(37%)</td> </tr> <tr> <td class="red_bold">Carbs</td> <td>37g</td> <td class="small_italic">(12%)</td> </tr> <tr> <td class="red_bold">Protein</td> <td>24g</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Sodium</td> <td>720mg</td> <td class="small_italic">(30%)</td> </tr> <tr> <td colspan="3" class="notes">Note: Values shown are for the default size and/or flavor.</td> </tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_learn_more_and_customize"></a></td></tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_add_to_my_meal_builder"></a></td></tr> </tbody> </table> </div> <div class="product_item"> <img src="images/product_icons/BigNTasty.png" height="115" width="99" alt="Big N&rsquo; Tasty"/> <div class="small_title">Big N&rsquo; Tasty</div> <table class="product_information" cellpadding="0" border="0" cellspacing="0"> <tbody> <tr> <td class="red_bold"></td> <td></td> <td class="small_italic">(Daily Value)</td> </tr> <tr> <td class="red_bold">Calories</td> <td>460</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Total Fat</td> <td>24g</td> <td class="small_italic">(37%)</td> </tr> <tr> <td class="red_bold">Carbs</td> <td>37g</td> <td class="small_italic">(12%)</td> </tr> <tr> <td class="red_bold">Protein</td> <td>24g</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Sodium</td> <td>720mg</td> <td class="small_italic">(30%)</td> </tr> <tr> <td colspan="3" class="notes">Note: Values shown are for the default size and/or flavor.</td> </tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_learn_more_and_customize"></a></td></tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_add_to_my_meal_builder"></a></td></tr> </tbody> </table> </div> <div class="product_item"> <img src="images/product_icons/BigNTasty.png" height="115" width="99" alt="Big N&rsquo; Tasty"/> <div class="small_title">Big N&rsquo; Tasty</div> <table class="product_information" cellpadding="0" border="0" cellspacing="0"> <tbody> <tr> <td class="red_bold"></td> <td></td> <td class="small_italic">(Daily Value)</td> </tr> <tr> <td class="red_bold">Calories</td> <td>460</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Total Fat</td> <td>24g</td> <td class="small_italic">(37%)</td> </tr> <tr> <td class="red_bold">Carbs</td> <td>37g</td> <td class="small_italic">(12%)</td> </tr> <tr> <td class="red_bold">Protein</td> <td>24g</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Sodium</td> <td>720mg</td> <td class="small_italic">(30%)</td> </tr> <tr> <td colspan="3" class="notes">Note: Values shown are for the default size and/or flavor.</td> </tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_learn_more_and_customize"></a></td></tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_add_to_my_meal_builder"></a></td></tr> </tbody> </table> </div> <div class="product_item"> <img src="images/product_icons/BigNTasty.png" height="115" width="99" alt="Big N&rsquo; Tasty"/> <div class="small_title">Big N&rsquo; Tasty</div> <table class="product_information" cellpadding="0" border="0" cellspacing="0"> <tbody> <tr> <td class="red_bold"></td> <td></td> <td class="small_italic">(Daily Value)</td> </tr> <tr> <td class="red_bold">Calories</td> <td>460</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Total Fat</td> <td>24g</td> <td class="small_italic">(37%)</td> </tr> <tr> <td class="red_bold">Carbs</td> <td>37g</td> <td class="small_italic">(12%)</td> </tr> <tr> <td class="red_bold">Protein</td> <td>24g</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Sodium</td> <td>720mg</td> <td class="small_italic">(30%)</td> </tr> <tr> <td colspan="3" class="notes">Note: Values shown are for the default size and/or flavor.</td> </tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_learn_more_and_customize"></a></td></tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_add_to_my_meal_builder"></a></td></tr> </tbody> </table> </div> <div class="product_item"> <img src="images/product_images/x115/chicken/PremCrispyChickenRanchBLT.png" height="115" width="115" alt="Premium Cripsy Chicken Ranch BLT"/> <div class="small_title">Premium Cripsy Chicken Ranch BLT</div> <table class="product_information" cellpadding="0" border="0" cellspacing="0"> <tbody> <tr> <td class="red_bold"></td> <td></td> <td class="small_italic">(Daily Value)</td> </tr> <tr> <td class="red_bold">Calories</td> <td>460</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Total Fat</td> <td>24g</td> <td class="small_italic">(37%)</td> </tr> <tr> <td class="red_bold">Carbs</td> <td>37g</td> <td class="small_italic">(12%)</td> </tr> <tr> <td class="red_bold">Protein</td> <td>24g</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Sodium</td> <td>720mg</td> <td class="small_italic">(30%)</td> </tr> <tr> <td colspan="3" class="notes">Note: Values shown are for the default size and/or flavor.</td> </tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_learn_more_and_customize"></a></td></tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_add_to_my_meal_builder"></a></td></tr> </tbody> </table> </div> <div class="product_item"> <img src="images/product_images/x115/sandwiches/FiletOFish.png" height="115" width="99" alt="Filet O Fish"/> <div class="small_title">Filet O Fish</div> <table class="product_information" cellpadding="0" border="0" cellspacing="0"> <tbody> <tr> <td class="red_bold"></td> <td></td> <td class="small_italic">(Daily Value)</td> </tr> <tr> <td class="red_bold">Calories</td> <td>460</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Total Fat</td> <td>24g</td> <td class="small_italic">(37%)</td> </tr> <tr> <td class="red_bold">Carbs</td> <td>37g</td> <td class="small_italic">(12%)</td> </tr> <tr> <td class="red_bold">Protein</td> <td>24g</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Sodium</td> <td>720mg</td> <td class="small_italic">(30%)</td> </tr> <tr> <td colspan="3" class="notes">Note: Values shown are for the default size and/or flavor.</td> </tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_learn_more_and_customize"></a></td></tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_add_to_my_meal_builder"></a></td></tr> </tbody> </table> </div> <div class="product_item"> <img src="images/product_icons/BigNTasty.png" height="115" width="99" alt="Big N&rsquo; Tasty"/> <div class="small_title">Big N&rsquo; Tasty</div> <table class="product_information" cellpadding="0" border="0" cellspacing="0"> <tbody> <tr> <td class="red_bold"></td> <td></td> <td class="small_italic">(Daily Value)</td> </tr> <tr> <td class="red_bold">Calories</td> <td>460</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Total Fat</td> <td>24g</td> <td class="small_italic">(37%)</td> </tr> <tr> <td class="red_bold">Carbs</td> <td>37g</td> <td class="small_italic">(12%)</td> </tr> <tr> <td class="red_bold">Protein</td> <td>24g</td> <td class="small_italic"></td> </tr> <tr> <td class="red_bold">Sodium</td> <td>720mg</td> <td class="small_italic">(30%)</td> </tr> <tr> <td colspan="3" class="notes">Note: Values shown are for the default size and/or flavor.</td> </tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_learn_more_and_customize"></a></td></tr> <tr><td colspan="3"><a href="#" class="acts_as_button en_add_to_my_meal_builder"></a></td></tr> </tbody> </table> </div> <div class="clear"></div> </div> </body> Below is the css code: div.small_title { font-size: 10px; color: #929292; text-align: center; max-width: 115px; line-height: 13px; padding-top: 5px; margin: 0 auto; } .product_item { position: relative; float:left; min-width: 35px; max-width: 189px; width: auto !important; text-align:center; border: 1px solid #CCC; } Please help me! Cheers!! Lokesh Yadav

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  • Method having an abstract class as a parameter

    - by Ferhat
    I have an abstract class A, where I have derived the classes B and C. Class A provides an abstract method DoJOB(), which is implemented by both derived classes. There is a class X which has methods inside, which need to call DoJOB(). The class X may not contain any code like B.DoJOB() or C.DoJOB(). Example: public class X { private A foo; public X(A concrete) { foo = concrete; } public FunnyMethod() { foo.DoJOB(); } } While instantiating class X I want to decide which derived class (B or C) must be used. I thought about passing an instance of B or C using the constructor of X. X kewl = new X(new C()); kewl.FunnyMethod(); //calls C.DoJOB() kewl = new X(new B()); kewl.FunnyMethod(); // calls B.DoJOB() My test showed that declaring a method with a parameter A is not working. Am I missing something? How can I implement this correctly? (A is abstract, it cannot be instantiated)

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  • In Ruby are there any related applications of the syntax: class << self ... end

    - by pez_dispenser
    class << self attr_accessor :n, :totalX, :totalY end The syntax above is used for defining class instance variables. But when I think about what syntax implies, it doesn't make any sense to me, so I'm wondering if this type of syntax is used for any other types of definitions. My point of confusion here is this: class << self The append operator normally means "add what's on the right to the object on the left". But in the context of this block, how does that add up to "put the contents of this block into the definition of the class instance rather than the instance"? For the same reason I'm confused as to why in one context class << self can define class instance variables while in another it seems to create class variables such as here: class Point # Instance methods go here class << self # Class methods go here end end

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  • Object of an abstract class

    - by webgenius
    Why is it not possible to create an object of an abstract class? I understand that the compiler creates a VTABLE with VPTR pointing to NULL. Does this prevent from creating an object of an abstract class?

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  • Best practice Unit testing abstract classes?

    - by Paul Whelan
    Hello I was wondering what the best practice is for unit testing abstract classes and classes that extend abstract classes. Should I test the abstract class by extending it and stubbing out the abstract methods and then test all the concrete methods? Then only test the methods I override and the abstract methods in the unit tests for objects that extend my abstract class. Should I have an abstract test case that can be used to test the methods of the abstract class and extend this class in my test case for objects that extend the abstract class? EDIT: My abstract class has some concrete methods. I would be interested to see what people are using. Thanks Paul

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  • UML class diagram - can aggregated object be part of two aggregated classes?

    - by user970696
    Some sources say that aggregation means that the class owns the object and shares reference. Lets assume an example where a company class holds a list of cars but departments of that company has list of cars used by them. class Department { list<Car> listOfCars; } class Company { list<Car> listOfCars; //initialization of the list } So in UML class diagram, I would do it like this. But I assume this is not allowed because it would imply that both company and department own the objects.. [COMPANY]<>------[CAR] [DEPARTMENT]<>---| //imagine this goes up to the car class

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  • Base class -> Derived class and vice-versa conversions in C++

    - by Ivan Nikolaev
    Hi! I have the following example code: #include <iostream> #include <string> using namespace std; class Event { public: string type; string source; }; class KeyEvent : public Event { public: string key; string modifier; }; class MouseEvent : public Event { public: string button; int x; int y; }; void handleEvent(KeyEvent e) { if(e.key == "ENTER") cout << "Hello world! The Enter key was pressed ;)" << endl; } Event generateEvent() { KeyEvent e; e.type = "KEYBOARD_EVENT"; e.source = "Keyboard0"; e.key = "SPACEBAR"; e.modifier = "none"; return e; } int main() { KeyEvent e = generateEvent(); return 0; } I can't compile it, G++ throws an error of kind: main.cpp: In function 'int main()': main.cpp:47:29: error: conversion from 'Event' to non-scalar type 'KeyEvent' requested I know that the error is obvious for C++ guru's, but I can't understand why I can't do the conversion from base class object to derived one. Can someone suggest me the solution of the problem that I have? Thx in advice

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  • Interface vs Abstract Class (general OO)

    - by Kave
    Hi, I have had recently two telephone interviews where I've been asked about the differences between an Interface and an Abstract class. I have explained every aspect of them I could think of, but it seems they are waiting for me to mention something specific, and I dont know what it is. From my experience I think the following is true, if i am missing a major point please let me know: Interface: Every single Method declared in an Interface will have to be implemented in the subclass. Only Events, Delegates, Properties (C#) and Methods can exist in a Interface. A class can implement multiple Interfaces. Abstract Class Only Abstract methods have to be implemented by the subclass. An Abstract class can have normal methods with implementations. Abstract class can also have class variables beside Events, Delegates, Properties and Methods. A class can only implement one abstract class only due non-existence of Multi-inheritance in C#. 1) After all that the interviewer came up with the question What if you had an Abstract class with only abstract methods, how would that be different from an interface? I didnt know the answer but I think its the inheritance as mentioned above right? 2) An another interviewer asked me what if you had a Public variable inside the interface, how would that be different than in Abstract Class? I insisted you can't have a public variable inside an interface. I didn't know what he wanted to hear but he wasn't satisfied either. Many Thanks for clarification, Kave See Also: When to use an interface instead of an abstract class and vice versa Interfaces vs. Abstract Classes How do you decide between using an Abstract Class and an Interface?

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  • Visual Studio: Design a UserControl class that derives from an abstract base class

    - by Marcel
    Hi All, I want to have an abstract base class for some of my custom UserControl's. The reason is obvious: they share some common properties and methods (a basic implementation of some elements of an interface actually), and I want to implement them only once. I have done this by defining my abstract base class: public abstract class ViewBase : UserControl, ISomeInterface Then I went to implement one of my views, as usual, with the designer: public partial class SpecialView : UserControl //all OK Up to here all is fine. Now I replace the derivation of my SpecialView class with the abstract base class: public partial class SpecialView : ViewBase //disrupts the designer Now, the designer in Visual Studio 2008 won't work anymore, stating: The designer must create an instance of type 'ViewBase' but it cannot because the type is declared as abstract. How can I circumvent this? I just do not want to have the same code copied for all those views. Info: there is a question question with virtual methods, instead of abstract classes, but there is no suitable solution for me.

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  • Building a database class in PHP

    - by Sprottenwels
    I wonder if I should write a database class for my application, and if so, how to accomplish it? Over there on SO, a guy mentioned it should be written as an abstract class. However, I can't understand why this would be a benefit. Do I understand correctly, that if I would write an abstract class, every other class that methods will need a database connection, could simply extend this abstract class and have it's own database object? If so, how is this different from a "normal" class where I could instantiate an database object? Another method would be to completely forget about my own class and to instantiate a mysqli object on demand. What do you recommend?

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  • Workaround for abstract attributes in Java

    - by deamon
    In Scala I would write an abstract class with an abstract attribute path: abstract class Base { val path: String } class Sub extends Base { override val path = "/demo/" } Java doesn't know abstract attributes and I wonder what would be the best way to work around this limitation. My ideas: a) constructor parameter abstract class Base { protected String path; protected Base(String path) { this.path = path; } } class Sub extends Base { public Sub() { super("/demo/"); } } b) abstract method abstract class Base { // could be an interface too abstract String getPath(); } class Sub extends Base { public String getPath() { return "/demo/"; } } Which one do you like better? Other ideas? I tend to use the constructor since the path value should not be computed at runtime.

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  • Linking a template class using another template class (error LNK2001)

    - by Luís Guilherme
    I implemented the "Strategy" design pattern using an Abstract template class, and two subclasses. Goes like this: template <class T> class Neighbourhood { public: virtual void alter(std::vector<T>& array, int i1, int i2) = 0; }; and template <class T> class Swap : public Neighbourhood<T> { public: virtual void alter(std::vector<T>& array, int i1, int i2); }; There's another subclass, just like this one, and alter is implemented in the cpp file. Ok, fine! Now I declare another method, in another class (including neighbourhood header file, of course), like this: void lSearch(/*parameters*/, Neighbourhood<LotSolutionInformation> nhood); It compiles fine and cleanly. When starting to link, I get the following error: 1>SolverFV.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall lsc::Neighbourhood<class LotSolutionInformation>::alter(class std::vector<class LotSolutionInformation,class std::allocator<class LotSolutionInformation> > &,int,int)" (?alter@?$Neighbourhood@VLotSolutionInformation@@@lsc@@UAEXAAV?$vector@VLotSolutionInformation@@V?$allocator@VLotSolutionInformation@@@std@@@std@@HH@Z)

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  • Abstract Methods in "Product" - Factory Method C#

    - by Regina Foo
    I have a simple class library (COM+ service) written in C# to consume 5 web services: Add, Minus, Divide, Multiply and Compare. I've created the abstract product and abstract factory classes. The abstract product named WS's code: public abstract class WS { public abstract double Calculate(double a, double b); public abstract string Compare(double a, double b); } As you see, when one of the subclasses inherits WS, both methods must be overridden which might not be useful in some subclasses. E.g. Compare doesn't need Calculate() method. To instantiate a new CompareWS object, the client class will call the CreateWS() method which returns a WS object type. public class CompareWSFactory : WSFactory { public override WS CreateWS() { return new CompareWS(); } } But if Compare() is not defined as abstract in WS, the Compare() method cannot be invoked. This is only an example with two methods, but what if there are more methods? Is it stupid to define all the methods as abstract in the WS class? My question is: I want to define abstract methods that are common to all subclasses of WS whereas when the factory creates a WS object type, all the methods of the subclasses can be invoked (overridden methods of WS and also the methods in subclasses). How should I do this?

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  • Java: reusable encapsulation with interface, abstract class or inner classes?

    - by HH
    I try to encapsulate. Exeption from interface, static inner class working, non-static inner class not working, cannot understand terminology: nested classes, inner classes, nested interfaces, interface-abstract-class -- sounds too Repetitive! Exception 'illegal type' from interface apparently because values being constants(?!) static interface userInfo { File startingFile=new File("."); String startingPath="dummy"; try{ startingPath=startingFile.getCanonicalPath(); }catch(Exception e){e.printStackTrace();} } Working code but no succes with non-static inner class import java.io.*; import java.util.*; public class listTest{ public interface hello{String word="hello word from Interface!";} public static class hej{ hej(){} private String hejo="hello hallo from Static class with image"; public void printHallooo(){System.out.println(hejo);} } public class nonStatic{ nonStatic(){} //HOW TO USE IT? public void printNonStatic(){System.out.println("Inside static class with an image!");} } public static void main(String[] args){ //INTERFACE TEST System.out.println(hello.word); //INNNER CLASS STATIC TEST hej h=new hej(); h.printHallooo(); //INNER CLASS NON-STATIC TEST nonStatic ns=new nonStatic(); ns.printNonStatic(); //IS there a way to it without STATIC? } } Output The above code works but how non-staticly? Output: hello word from Interface! hello hallo from Static class with image! StaticPrint without an image of the class! Related Nesting classes inner classes? interfacses

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  • How to easily substitute a Base class

    - by JTom
    Hi, I have the following hierarchy of classes class classOne { virtual void abstractMethod() = 0; }; class classTwo : public classOne { }; class classThree : public classTwo { }; All classOne, classTwo and classThree are abstract classes, and I have another class that is defining the pure virtual methods class classNonAbstract : public classThree { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; And right now I need it differently...I need it like class classNonAbstractOne : public classOne { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; class classNonAbstractTwo : public classTwo { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; and class classNonAbstractThree : public classThree { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; But all the nonAbstract classes have the same new methods, with the same code...and I would like to avoid copying all the methods and it's code to every nonAbstract class. How could I accomplish that? Hopefully it's understandable...

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  • When to use abstract classes instead of interfaces and extension methods in C#?

    - by Gulshan
    "Abstract class" and "interface" are similar type of ideas, while interface being more abstract. One need of abstract classes was to provide method implementations for the derived classes. But in C#, that need has also been reduced by lately introduced extension methods. So, in C#, when should we use abstract classes instead of using interfaces and extension methods associated with the interface? And now, we can use 'Properties' in interfaces also. A notable example of interface+ extension methods is the Heavily used IEnumerable and it's helper methods. You use Linq and it's all by this extension methods!

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  • When to use abstract classes instead of interfaces and extension methods in C#?

    - by Gulshan
    "Abstract class" and "interface" are similar type of ideas, while interface being more abstract. One need of abstract classes was to provide method implementations for the derived classes. But in C#, that need has also been reduced by lately introduced extension methods. So, in C#, when should we use abstract classes instead of using interfaces and extension methods associated with the interface? And now, we can use 'Properties' in interfaces also. A notable example of interface+ extension methods is the Heavily used IEnumerable and it's helper methods. You use Linq and it's all by this extension methods!

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  • Should all public methods in an abstract class be marked virtual?

    - by Justin Pihony
    I recently had to update an abstract base class on some OSS that I was using so that it was more testable by making them virtual (I could not use an interface as it combined two). This got me thinking whether I should mark all of the methods that I needed virtual, or if I should mark every public method/property virtual. I generally agree with Roy Osherove that every method should be made virtual, but I came across this article that got me thinking about whether this was necessary or not. I am going to limit this down to abstract classes for simplicity, however (whether all concrete public methods should be virtual is especially debatable, I am sure). I could see where you might want to allow a sub-class to use a method, but not want it overriding the implementation. However, as long as you trust that Liskov's Substitution Principle will be followed, then why would you not allow it to be overriden? By marking it abstract, you are forcing a certain override anyway, so, it seems to me that all public methods inside of an abstract class should indeed be marked virtual. However, I wanted to ask in case there was something I might not be thinking. Should all public methods within an abstract class be made virtual?

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  • Why does C# allow abstract class with no abstract members?

    - by fatcat1111
    The C# spec, section 10.1.1.1, states: An abstract class is permitted (but not required) to contain abstract members. This allows me to create classes like this: public abstract class A { public void Main() { // it's full of logic! } } This is really a concrete class; it's only abstract in so far as one can't instantiate it. If inheritors don't actually have to provide implementation, then why call it abstract?

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  • Python: query a class's parent-class after multiple derivations ("super()" does not work)

    - by henry
    Hi, I have built a class-system that uses multiple derivations of a baseclass (object-class1-class2-class3): class class1(object): def __init__(self): print "class1.__init__()" object.__init__(self) class class2(class1): def __init__(self): print "class2.__init__()" class1.__init__(self) class class3(class2): def __init__(self): print "class3.__init__()" class2.__init__(self) x = class3() It works as expected and prints: class3.__init__() class2.__init__() class1.__init__() Now I would like to replace the 3 lines object.__init__(self) ... class1.__init__(self) ... class2.__init__(self) with something like this: currentParentClass().__init__() ... currentParentClass().__init__() ... currentParentClass().__init__() So basically, i want to create a class-system where i don't have to type "classXYZ.doSomething()". As mentioned above, I want to get the "current class's parent-class". Replacing the three lines with: super(type(self), self).__init__() does NOT work (it always returns the parent-class of the current instance - class2) and will result in an endless loop printing: class3.__init__() class2.__init__() class2.__init__() class2.__init__() class2.__init__() ... So is there a function that can give me the current class's parent-class? Thank you for your help! Henry -------------------- Edit: @Lennart ok maybe i got you wrong but at the moment i think i didn't describe the problem clearly enough.So this example might explain it better: lets create another child-class class class4(class3): pass now what happens if we derive an instance from class4? y = class4() i think it clearly executes: super(class3, self).__init__() which we can translate to this: class2.__init__(y) this is definitly not the goal(that would be class3.__init__(y)) Now making lots of parent-class-function-calls - i do not want to re-implement all of my functions with different base-class-names in my super()-calls.

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  • How to use derived class shared variables in shared methods of base class

    - by KoolKabin
    Hi guys, I am trying to add shared members in derived classes and use that values in base classes... I have base class DBLayer public shared function GetDetail(byval UIN as integer) dim StrSql = string.format("select * from {0} where uin = {1}", tablename, uin) .... end function end class my derived class class User inherits dblayer public shared tabledname as string = "users" end class class item inherits dblayer public shared tabledname as string = "item" end class class category inherits dblayer public shared tabledname as string = "category" end class currently there is error using the tablename variable of derived class in base class but i want to use it... coz i dun know other techniques... if other solutions are better then u can post it or u can say how can i make it work? confused...

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  • Advantages of Singleton Class over Static Class?

    Point 1)Singleton We can get the object of singleton and then pass to other methods.Static Class We can not pass static class to other methods as we pass objectsPoint 2) Singleton In future, it is easy to change the logic of of creating objects to some pooling mechanism. Static Class Very difficult to implement some pooling logic in case of static class. We would need to make that class as non-static and then make all the methods non-static methods, So entire your code needs to be changed.Point3:) Singleton Can Singletone class be inherited to subclass? Singleton class does not say any restriction of Inheritence. So we should be able to do this as long as subclass is also inheritence.There's nothing fundamentally wrong with subclassing a class that is intended to be a singleton. There are many reasons you might want to do it. and there are many ways to accomplish it. It depends on language you use.Static Class We can not inherit Static class to another Static class in C#. Think about it this way: you access static members via type name, like this: MyStaticType.MyStaticMember(); Were you to inherit from that class, you would have to access it via the new type name: MyNewType.MyStaticMember(); Thus, the new item bears no relationships to the original when used in code. There would be no way to take advantage of any inheritance relationship for things like polymorphism. span.fullpost {display:none;}

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  • Advantages of Singleton Class over Static Class?

    Point 1) Singleton We can get the object of singleton and then pass to other methods. Static Class We can not pass static class to other methods as we pass objects Point 2) Singleton In future, it is easy to change the logic of of creating objects to some pooling mechanism. Static Class Very difficult to implement some pooling logic in case of static class. We would need to make that class as non-static and then make all the methods non-static methods, So entire your code needs to be changed. Point3:) Singleton Can Singletone class be inherited to subclass? Singleton class does not say any restriction of Inheritence. So we should be able to do this as long as subclass is also inheritence.There's nothing fundamentally wrong with subclassing a class that is intended to be a singleton. There are many reasons you might want to do it. and there are many ways to accomplish it. It depends on language you use. Static Class We can not inherit Static class to another Static class in C#. Think about it this way: you access static members via type name, like this: MyStaticType.MyStaticMember(); Were you to inherit from that class, you would have to access it via the new type name: MyNewType.MyStaticMember(); Thus, the new item bears no relationships to the original when used in code. There would be no way to take advantage of any inheritance relationship for things like polymorphism. span.fullpost {display:none;}

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