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  • A public struct inside a class

    - by Koning Baard
    I am new to C++, and let's say I have two classes: Creature and Human: /* creature.h */ class Creature { private: public: struct emotion { /* All emotions are percentages */ char joy; char trust; char fear; char surprise; char sadness; char disgust; char anger; char anticipation; char love; }; }; /* human.h */ class Human : Creature { }; And I have this in my main function in main.cpp: Human foo; My question is: how can I set foo's emotions? I tried this: foo->emotion.fear = 5; But GCC gives me this compile error: error: base operand of '-' has non-pointer type 'Human' This: foo.emotion.fear = 5; Gives: error: 'struct Creature::emotion' is inaccessible error: within this context error: invalid use of 'struct Creature::emotion' Can anyone help me? Thanks P.S. No I did not forget the #includes

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  • Calling base class constructor

    - by The Void
    In the program below, is the line Derived(double y): Base(), y_(y) correct/allowed? That is, does it follow ANSI rules? #include <iostream> class Base { public: Base(): x_(0) { std::cout << "Base default constructor called" << std::endl; } Base(int x): x_(x) { std::cout << "Base constructor called with x = " << x << std::endl; } void display() const { std::cout << x_ << std::endl; } protected: int x_; }; class Derived: public Base { public: Derived(): Base(1), y_(1.2) { std::cout << "Derived default constructor called" << std::endl; } Derived(double y): Base(), y_(y) { std::cout << "Derived constructor called with y = " << y << std::endl; } void display() const { std::cout << Base::x_ << ", " << y_ << std::endl; } private: double y_; }; int main() { Base b1; b1.display(); Derived d1; d1.display(); std::cout << std::endl; Base b2(-9); b2.display(); Derived d2(-8.7); d2.display(); return 0; }

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  • C++ privately contructed class

    - by Nona Urbiz
    How can I call a function and keep my constructor private? If I make the class static, I need to declare an object name which the compiler uses to call the constructor, which it cannot if the constructor is private (also the object would be extraneous). Here is the code I am attempting to use (it is not compilable): I want to keep the constructor private because I will later be doing a lot of checks before adding an object, modifying previous objects when all submitted variables are not unique rather than creating new objects. #include <iostream> #include <fstream> #include <regex> #include <string> #include <list> #include <map> using namespace std; using namespace tr1; class Referral { public: string url; map<string, int> keywords; static bool submit(string url, string keyword, int occurrences) { //if(Referrals.all.size == 0){ // Referral(url, keyword, occurrences); //} } private: list<string> urls; Referral(string url, string keyword, int occurrences) { url = url; keywords[keyword] = occurrences; Referrals.all.push_back(this); } }; struct All { list<Referral> all; }Referrals; int main() { Referral.submit("url", "keyword", 1); }

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  • java class that simulates a simple database table

    - by ericso
    I have a collection of heterogenous data that I pull from a database table mtable. Then, for every unique value uv in column A, I compute a function of (SELECT * FROM mtable WHERE A=uv). Then I do the same for column B, and column C. There are rather a lot of unique values, so I don't want to hit the db repeatedly - I would rather have a class that replicates some of the functionality (most importantly some version of SELECT WHERE). Additionally, I would like to abstract the column names away from the class definition, if that makes any sense - the constructor should take a list of names as a parameter, and also, I suppose, a list of types (right now this is just a String[], which seems hacky). I'm getting the initial data from a RowSet. I've more or less done this by using a hashmap that maps Strings to lists/arrays of Objects, but I keep getting bogged down in comparisons and types, and am thinking that my current implementation really isn't as clean and clear as it could be. I'm pretty new to java, also, and am not sure if I'm not going down a completely incorrect path. Does anyone have any suggestions?

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  • Car Class (first time with classes)

    - by user2967605
    For an assignment I needed to use a class named car and have it display the make and model, and also have the speed increase by 5 when you use accelerate and decrease by 5 when you brake. My teacher helped me along the way but when I got to the end I couldn't get it to run. Could someone correct me and tell my why it's wrong? Imp--------- #include <iostream> #include <string> using namespace std; void accelerate() { int speed; speed = speed + 5; } void brake() { int speed; speed = speed - 5; } Header #include <iostream> #include <string> using namespace std; class car { public: car(int getYear, string getMake); void accelerate(); void brake(); private: int year; string make; int speed; }; CarClass.cpp #include <string> #include "CarClass.h" using namespace std; int main() { car.(2013,"Kia") car.accelerate() car.brake() }

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  • MVC repository pattern design decision

    - by bradjive
    I have an asp .net MVC application and recently started implementing the repository pattern with a service validation layer, much like this. I've been creating one repository/service for each model that I create. Is this overkill? Instead, should I create one repository/service for each logical business area that provides CRUD for many different models? To me, it seems like I'm either cluttering the project tree with many files or cluttering a class with many methods. 6 one way half dozen the other. Can you think of any good arguments either way?

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  • Objective-C wrapper API design methodology

    - by Wade Williams
    I know there's no one answer to this question, but I'd like to get people's thoughts on how they would approach the situation. I'm writing an Objective-C wrapper to a C library. My goals are: 1) The wrapper use Objective-C objects. For example, if the C API defines a parameter such as char *name, the Objective-C API should use name:(NSString *). 2) The client using the Objective-C wrapper should not have to have knowledge of the inner-workings of the C library. Speed is not really any issue. That's all easy with simple parameters. It's certainly no problem to take in an NSString and convert it to a C string to pass it to the C library. My indecision comes in when complex structures are involved. Let's say you have: struct flow { long direction; long speed; long disruption; long start; long stop; } flow_t; And then your C API call is: void setFlows(flow_t inFlows[4]); So, some of the choices are: 1) expose the flow_t structure to the client and have the Objective-C API take an array of those structures 2) build an NSArray of four NSDictionaries containing the properties and pass that as a parameter 3) create an NSArray of four "Flow" objects containing the structure's properties and pass that as a parameter My analysis of the approaches: Approach 1: Easiest. However, it doesn't meet the design goals Approach 2: For some reason, this seems to me to be the most "Objective-C" way of doing it. However, each element of the NSDictionary would have to be wrapped in an NSNumber. Now it seems like we're doing an awful lot just to pass the equivalent of a struct. Approach 3: Seems the cleanest to me from an object-oriented standpoint and the extra encapsulation could come in handy later. However, like #2, it now seems like we're doing an awful lot (creating an array, creating and initializing objects) just to pass a struct. So, the question is, how would you approach this situation? Are there other choices I'm not considering? Are there additional advantages or disadvantages to the approaches I've presented that I'm not considering?

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  • Python class design - Splitting up big classes into multiple ones to group functionality

    - by Ivo Wetzel
    OK I've got 2 really big classes 1k lines each that I currently have split up into multiple ones. They then get recombined using multiple inheritance. Now I'm wondering, if there is any cleaner/better more pythonic way of doing this. Completely factoring them out would result in endless amounts of self.otherself.do_something calls, which I don't think is the way it should be done. To make things clear here's what it currently looks like: from gui_events import GUIEvents # event handlers from gui_helpers import GUIHelpers # helper methods that don't directly modify the GUI # GUI.py class GUI(gtk.Window, GUIEvents, GUIHelpers): # general stuff here stuff here One problem that is result of this is Pylint complaining giving me trillions of "init not called" / "undefined attribute" / "attribute accessed before definition" warnings.

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  • UiElement from abstract class

    - by plotnick
    I placed a control into a grid. let's say the control is derived from public class 'ButBase' which is derived in its turn from System.Windows.Controls.Button. The code normally compiles and app works just fine. But there's something really annoying. When you try to switch to xaml-design tab it will say 'The document root element is not supported by the visual designer', which is normal and I'm totally okay with that, but the thing is, that all the xaml code is underlined and VS2010 says: 'Cannot create an instance of ButBase' although still normally compiles and able to run. I've tried the same code in VS2008, it said that needs to see a public parameterless constructor in the ButBase, and even after I put one it showed the same error. What do I miss here?

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  • UiElement based on another class

    - by plotnick
    I placed a control into a grid. let's say the control is derived from public class 'ButBase' which is derived in its turn from System.Windows.Controls.Button. The code normally compiles and app works just fine. But there's something really annoying. When you try to switch to xaml-design tab it will say 'The document root element is not supported by the visual designer', which is normal and I'm totally okay with that, but the thing is, that all the xaml code is underlined and VS2010 says: 'Cannot create an instance of ButBase' although still normally compiles and able to run. I've tried the same code in VS2008, it said that needs to see a public parameterless constructor in the ButBase, and even after I put one it showed the same error. What do I miss here?

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  • Design question for WinForms (C#) app, using Entity Framework

    - by cdotlister
    I am planning on writing a small home budget application for myself, as a learning excercise. I have built my database (SQL Server), and written a small console application to interact with it, and test out scenarios on my database. Once I am happy, my next step would be to start building the application - but I am already wondering what the best/standard design would be. I am palnning on using Entity Framework for handling my database entities... then linq to sql/objects for getting the data, all running under a WinForms (for now) application. My plan (I've never used EF... and most of my development background is Web apps) is to have my database... with Entity Framework in it's own project.. which has the connection to the database. This project would expose methods such as 'GetAccount()', 'GetAccount(int accountId)' etc. I'd then have a service project that references my EF project. And on top of that, my GUI project, which makes the calls to my service project. But I am stuck. Lets say I have a screen that displays a list of Account types (Debit, Credit, Loan...). Once I have selected one, the next drop down shows a list of accounts I have that suite that account type. So, my OnChange event on my DropDown on the account type control will make a call to the serviceLayer project, 'GetAccountTypes()', and I would expect back a List< of Account Types. However, the AccountType object ... what is that? That can't be the AccountType object from my EF project, as my GUI project doesn't have reference to it. Would I have to have some sort of Shared Library, shared between my GUI and my Service project, with a custom built AccountType object? The GUI can then expect back a list of these. So my service layer would have a method: public List<AccountType> GetAccountTypes() That would then make a call to a custom method in my EF project, which would probably be the same as the above method, except, it returns an list of EF.Data.AccountType (The Entity Framework generated Account Type object). The method would then have the linq code to get the data as I want it. Then my service layer will get that object, and transform it unto my custom AccountType object, and return it to the GUI. Does that sound at all like a good plan?

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  • ERD Design help meeded

    - by Mobi
    Hello guyz, I am new to ERD and stuff.Earlier i was drawing an erd that issued me some problems. the name of two entities in focus is "Bus" and "Passenger".What shall be the relationship between them. I think it should be many to many since one passenger can travel in many buses and a bus can give ride to many passengers.But one of my friend insisted that its a one-to-many relationship(A bus can have many passengers but a passenger can travel in only one bus).Plz let me know what's right. Also , whats the relationship between a class,students. Any help is appreciated.

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  • Clear all class variables between instances

    - by ensnare
    This is probably a stupid question, but what's the best way to clear class variables between instances? I know I could reset each variable individually in the constructor; but is there a way to do this in bulk? Or am I doing something totally wrong that requires a different approach? Thanks for helping ... class User(): def __init__(self): #RESET ALL CLASS VARIABLES def commit(self): #Commit variables to database >>u = User() >>u.name = 'Jason' >>u.email = '[email protected]' >>u.commit() So that each time User is called the variables are fresh. Thanks.

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  • jquery .hide() bug in safari

    - by phil crowe
    ive been having issues with this hide bug thats only affecting safari. This is a simple vertical scroller that hides the first element in the list then shows the last. and works in everything apart from safari. the problem seems to be that the divs im working with here share the same class but have unique ids like #mycollectioncomment1, #mycollectioncomment2, #mycollectioncomment3 etc... however hiding just one of these divs hides all the other divs that share the same class. Ive tried .fadeOut(0) that everyone suggests as the work around but it just doesnt work here. var commentListCount = $(".myCollectionLatest").size(); var mycollclickCount = 0; var showingcomments = 5; if ($('.licomment').size() > 0) { showingcomments = 4; //alert("this"); } if ($('.lookInSeasonList').size() > 0) { showingcomments = 5; } if ($('.lookDescMiddle').size() > 0) { showingcomments = 8; } if ($('.MyCollectionsCollectionHolder').size() > 0) { showingcomments = 5; } // if (commentListCount > 5) { $(".myCollectionLatest").hide(); for (i = 0; i < showingcomments; i++) { $("#mycollectioncomment" + i).show(); } $('#mycolldown').click(function () { var element1, element2; if (showingcomments <= commentListCount) { mycollclickCount++; element1 = $("#mycollectioncomment" + mycollclickCount.toString()); element2 = $("#mycollectioncomment" + showingcomments.toString()); element1.closest('.licomment').hide(); element2.closest('.licomment').show(); showingcomments++; } }); $('#mycollup').click(function () { if (showingcomments <= 5) { } else { $("#mycollectioncomment" + mycollclickCount.toString()).show(); $("#mycollectioncomment" + mycollclickCount.toString()).closest('.licomment').show(); mycollclickCount--; showingcomments--; $("#mycollectioncomment" + showingcomments.toString()).hide(); $("#mycollectioncomment" + showingcomments.toString()).closest('.licomment').show(); } }); ---html markup --- <div style="width:260px; height:975px; float:left; border-right:solid 1px #e70079; border-bottom:solid 1px #e70079; border-left:solid 1px #e70079; margin-top:180px;"> <h2 align="center"> <br /> COLLECTION LATEST </h2> <img src="/images/my-collection/black-up.jpg" id="mycollup" /><ul><li class="licomment"><div class="myCollectionLatest" id="mycollectioncomment1"><div style="float:left;"><div class="colltoppic"><a href="/my-collection.aspx?memberId=6855"><img src="/media/6855/makeuo_main.jpg" width="74" height="74" onerror="ImgError(this);" /></a></div><div class="collbottompic" /><div style="float:left; position:absolute; margin-left:83px; margin-top:-84px;" class="mycolllatestlinks"><b><a href="/my-collection.aspx?memberId=6855" class="usernamelinkdiv">CHARLOTTE</a> SAID ABOUT <span class="pinkTxt"><br /><a href="/products/face/powder/pressed-powder.aspx">PRESSED POWDER</a></span></b><p>put this on after foundation. its the best cover powder + re... </p></div><div class="randomCommentsSeeMore"><span class="pinkTxt"><a href="/my-collection.aspx?memberId=6855"> See more <img src="/images/navControls/more-arrow.jpg" alt="see more" /></a></span></div></div></div></li><li class="licomment"><div class="myCollectionLatest" id="mycollectioncomment2"><div style="float:left;"><div class="colltoppic"><a href="/my-collection.aspx?memberId=6331"><img src="/media/6331/26462_1267423081357_1103204986_2592317_7875205_n_main.jpg" width="74" height="74" onerror="ImgError(this);" /></a></div><div class="collbottompic" /><div style="float:left; 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  • Buddy List: Relational Database Table Design

    - by huntaub
    So, the modern concept of the buddy list: Let's say we have a table called Person. Now, that Person needs to have many buddies (of which each buddy is also in the person class). The most obvious way to construct a relationship would be through a join table. i.e. buddyID person1_id person2_id 0 1 2 1 3 6 But, when a user wants to see their buddy list, the program would have to check the column 'person1_id' and 'person2_id' to find all of their buddies. Is this the appropriate way to implement this kind of table, or would it be better to add the record twice.. i.e. buddyID person1_id person2_id 0 1 2 1 2 1 So that only one column has to be searched. Thanks in advance.

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  • Validating class and superclass on RoR

    - by Luís Guilherme
    In ruby, you have an attribute called "type" which is the class of the object. Rails stores this at the database in a column called type. So, if I have several blog "types", I can do something like this def create @blog = Blog.new(params[:blog]) @blog[:type] = params[:blog][:type] # ... end If I add someone like this, and then load it, and ask its class (for instance, at the console), I have the right class name answered back. However, when I save it afterwards, rails will run only the superclass validators, not the ones I defined in the subclass. How should I make rails run the subclass validators?

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  • quantity of measurable units design pattern

    - by Berryl
    Hello I am thinking through a nice pattern to be useful across domains of measurable units (ie, Length, Time) and came up with the following use case and initial classes, and of course, questions! 1) Does a Composite pattern help or complicate? 2) Should the Convert method(s) in the ComposityNode be a separate converter class? All comments appreciated. Cheers, Berryl Example Use Case: var inch = new ConvertableUnit("inch", 1) var foot = new ConvertableUnit("foot", 12) var imperialUnits = new CompositeConvertableUnit("imperial units", .024) imperialUnits.AddChild(inch) imperialUnits.AddChild(foot) var meter = new ConvertableUnit("meter", 1) var millimeter = new ConvertableUnit("millimeter ", .001) var imperialUnits = new CompositeConvertableUnit("metric units", 1) imperialUnits.AddChild(meter) imperialUnits.AddChild(millimeter) var oneInch = new Quantity(1, inch); var oneFoot = new Quantity(1, foot); oneFoot.ToBase() // "12 inches" var oneMeter = new Quantity(1, meter); oneInch.ToBase() // .024 meters Possible Solution ConvertableUnit : Node double Rate string Name Quantity ConvertableUnit Unit double Amount CompositeConvertableUnit : Node ISet<ConvertableUnit> _children ConvertableUnit BaseUnit {get{ return _children.Where(c=>c.Rate == 1).First() } } Quantity ConvertTo(Quantity from, Quantity to) Quantity ToBase(Quantity from);

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  • Add child to scene from within a class.

    - by Fecal Brunch
    Hi, I'm new to flash in general and have been writing a program with two classes that extend MovieClip (Stems and Star). I need to create a new Stems object as a child of the scene when the user stops dragging a Star object, but do not know how to reference the scene from within the Star class's code. I've tried passing the scene into the constructor of the Star and doing sometihng like: this.scene.addChild (new Stems ()); But apparently that's not how to do it... Below is the code for Stems and Stars, any advice would be appreciated greatly. package { import flash.display.MovieClip; import flash.events.*; import flash.utils.Timer; public class Stems extends MovieClip { public const centreX=1026/2; public const centreY=600/2; public var isFlowing:Boolean; public var flowerType:Number; public const outerLimit=210; public const innerLimit=100; public function Stems(fType:Number) { this.isFlowing=false; this.scaleX=this.scaleY= .0007* distanceFromCentre(this.x, this.y); this.setXY(); trace(distanceFromCentre(this.x, this.y)); if (fType==2) { gotoAndStop("Aplant"); } } public function distanceFromCentre(X:Number, Y:Number):int { return (Math.sqrt((X-centreX)*(X-centreX)+(Y-centreY)*(Y-centreY))); } public function rotateAwayFromCentre():void { var theX:int=centreX-this.x; var theY:int = (centreY - this.y) * -1; var angle = Math.atan(theY/theX)/(Math.PI/180); if (theX<0) { angle+=180; } if (theX>=0&&theY<0) { angle+=360; } this.rotation = ((angle*-1) + 90)+180; } public function setXY() { do { var tempX=Math.random()*centreX*2; var tempY=Math.random()*centreY*2; } while (distanceFromCentre (tempX, tempY)>this.outerLimit || distanceFromCentre (tempX, tempY)<this.innerLimit); this.x=tempX; this.y=tempY; rotateAwayFromCentre(); } public function getFlowerType():Number { return this.flowerType; } } } package { import flash.display.MovieClip; import flash.events.*; import flash.utils.Timer; public class Star extends MovieClip { public const sWide=1026; public const sTall=600; public var startingX:Number; public var startingY:Number; public var starColor:Number; public var flicker:Timer; public var canUpdatePos:Boolean=true; public const innerLimit=280; public function Star(color:Number, basefl:Number, factorial:Number) { this.setXY(); this.starColor=color; this.flicker = new Timer (basefl + factorial * (Math.ceil(100* Math.random ()))); this.flicker.addEventListener(TimerEvent.TIMER, this.tick); this.addEventListener(MouseEvent.MOUSE_OVER, this.hover); this.addEventListener(MouseEvent.MOUSE_UP, this.drop); this.addEventListener(MouseEvent.MOUSE_DOWN, this.drag); this.addChild (new Stems (2)); this.flicker.start(); this.updateAnimation(0, false); } public function distanceOK(X:Number, Y:Number):Boolean { if (Math.sqrt((X-(sWide/2))*(X-(sWide/2))+(Y-(sTall/2))*(Y-(sTall/2)))>innerLimit) { return true; } else { return false; } } public function setXY() { do { var tempX=this.x=Math.random()*sWide; var tempY=this.y=Math.random()*sTall; } while (distanceOK (tempX, tempY)==false); this.startingX=tempX; this.startingY=tempY; } public function tick(event:TimerEvent) { if (this.canUpdatePos) { this.setXY(); } this.updateAnimation(0, false); this.updateAnimation(this.starColor, false); } public function updateAnimation(color:Number, bright:Boolean) { var brightStr:String; if (bright) { brightStr="bright"; } else { brightStr="low"; } switch (color) { case 0 : this.gotoAndStop("none"); break; case 1 : this.gotoAndStop("N" + brightStr); break; case 2 : this.gotoAndStop("A" + brightStr); break; case 3 : this.gotoAndStop("F" + brightStr); break; case 4 : this.gotoAndStop("E" + brightStr); break; case 5 : this.gotoAndStop("S" + brightStr); break; } } public function hover(event:MouseEvent):void { this.updateAnimation(this.starColor, true); this.canUpdatePos=false; } public function drop(event:MouseEvent):void { this.stopDrag(); this.x=this.startingX; this.y=this.startingY; this.updateAnimation(0, false); this.canUpdatePos=true; } public function drag(event:MouseEvent):void { this.startDrag(false); this.canUpdatePos=false; } } }

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  • JavaScript Resource Management Design Pattern

    - by Adam
    As a web developer, a common problem I find myself tackling is waiting for something to load before doing something else. In particular, I often hide (using either display: none; or visibility: hidden; depending on the situation) elements while waiting for a background image or a CSS file to load. Consider this example from Last.FM. They overlay a semi-transparant PNG over each album art image so that it looks like it's inside a jewel-case. They let it load when it loads, so depending on your internet speed, you may see the art image by itself (without the overlay) temporarily. In this case, the album art looks fine without the jewel-case effect. But in similar situations, I have found that I don't want the user to see the site's design mangled as resources incrementally load. So, in rare cases I have hidden everything from the user until the whole kit and kaboodle has loaded. But this is often a pain to write out, and may force the user to wait for a pretty long time to see anything (besides "loading..." text). I can think of (and have used on occasion) some obvious solutions/compromises: Use some inline CSS so that as certain parts of the DOM load and render, they will immediately have the correct size/position/etc. Immediately render the navigation part of the site, so that if the user wanted to use the current page purely to get somewhere else, they don't have to wait for the rest to load. Load pixelated images first as placeholders for layout while lazy-loading higher quality images as replacements. Something quirky like using a cute animated gif to distract the user during a "loading..." phase. Show useful information as a reference while loading the full UI. (Something akin to Gmail Inbox Preview, etc.) (Sorry if my question was basically just asked and answered...) Despite all of these ideas, I still find myself hoping there are better ways of doing some of these things. So I guess what I'm looking for is some inspiration and/or any creative ways of dealing with this problem that you guys may have seen out in the wild.

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  • Iphone -- init method of an abstract class

    - by William Jockusch
    I want to create classes Car, Vehicle, and Airplane with the following properties: Car and Airplane are both subclasses of Vehicle. Car and Airplane both have an initWithString method. The acceptable input strings for Car's and Airplane's initWithString methods do not overlap. Vehicle is "almost abstract", in the sense that any initialized instance should be either a Car or an Airplane. It is possible to pass a string into Vehicle and get back an instance of Car, an instance of Airplane, or nil, depending on the input string. Any particular design pattern I should prefer? In particular for Vehicle's initWithString and/or newVehicleWithString methods.

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  • Compiler doesn't find methods from base class

    - by Paul
    I am having a problem with my virtual methods in a derived class. Here are my (simplified) C++ classes. class Base virtual method accept( MyVisitor1* v ) { /*implementation is here*/ }; virtual method accept( MyVisitor2* v ) { /*implementation is here*/ }; virtual method accept( MyVisitor3* v ) { /*implementation is here*/ }; class DerivedClass virtual method accept( MyVisitor2* v ) { /*implementation is here*/ }; The following use causes VS 2005 to give: "error C2664: 'DerivedClass::accept' : cannot convert parameter 1 from 'Visitor1*' to 'Visitor2 *'". DerivedClass c; MyVisitor1 v1; c.accept(v1); I was expecting the compiler to find and call Base::accept(MyVisitor1) for my DerivedClass as well. Obviously this is not working, but I don't understand why. Any ideas? Thanks, Paul

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  • Is extending a singleton class wrong?

    - by Anwar Shaikh
    I am creating a logger for an application. I am using a third party logger library. In which logger is implemented as singleton. I extended that logger class because I want to add some more static functions. In these static functions I internally use the instance (which is single) of Logger(which i inherited). I neither creates instance of MyLogger nor re-implemented the getInstance() method of super class. But I am still getting warnings like destructor of MyLogger can not be created as parent class (Loggger) destructor is not accessible. I want to know, I am I doing something wrong? Inheriting the singleton is wrong or should be avoided??

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  • Dependency Injection & Singleton Design pattern

    - by SysAdmin
    How do we identify when to use dependency injection or singleton pattern. I have read in lot of websites where they say "Use Dependency injection over singleton pattern". But I am not sure if I totally agree with them. For my small or medium scale projects I definitely see the use of singleton pattern straightforward. For example Logger. I could use Logger.GetInstance().Log(...) But, instead of this, why do I need to inject every class I create, with the logger's instance?.

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  • Make Java parent class not part of the interface

    - by Bart van Heukelom
    (This is a hypothetical question for discussion, I have no actual problem). Say that I'm making an implementation of SortedSet by extending LinkedHashMap: class LinkedHashSortedMapThing extends LinkedHashMap implements SortedSet { ... } Now programmers who use this class may do LinkedHashMap x = new LinkedHashSortedMapThing(); But what if I consider the extending of LinkedHashMap an implementation detail, and do not want it to be a part of the class' contract? If people use the line above, I can no longer freely change this detail without worrying about breaking existing code. Is there any way to prevent this sort of thing, other than favouring composition over inheritance (which is not always possible due to private/protected members)?

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  • Design pattern: polymorphisim for list of objects

    - by ziang
    Suppose I have a class A, and A1, A2 inherits from A. There are 2 functions: List<A1> getListA1(){...} List<A2> getListA2(){...} Now I want to do something similar to both A1 and A2 in another function public void process(List<A>){...} If I want to pass the instance of either ListA1 or ListA2, of course the types doesn't match because the compiler doesn't allow the coercion from List< A1 to List< A. I can't do something like this: List<A1> listA1 = getListA1(); List<A> newList = (List<A>)listA1; //this is not allowed. So what is the best approach to the process()? Is there any way to do it in a universal way rather than write the similar code to both List and List?

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