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  • how to get variable stored in another object using objective c

    - by mac
    Hi All SaveNotes *saveNotes = [[SaveNotes alloc]initWithTitleString:title descrString:descr]; [titleDescrObjects addObject:saveNotes]; [saveNotes release]; from the above code i have saved title,descr to a class SaveNotes , and then i have stored that object in my NSMutableArray - titleDescrObjects, Its working fine, i need to get particular objects "descr" alone, how to get the descr from objectAtIndex:i i am trying for (int i=0; i<[titleDescrObjects count]; i++) { NSLog(@"\n ((%@))\n",[titleDescrObjects objectAtIndex:i].descr); } Thanks in advance,

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  • Skin Object Tokens for DotNetNuke 5 - 8 Videos

    In this tutorial we demonstrate how to use Skin Object Tokens in DotNetNuke v5 and above. Skin Object tokens are a new skinning method introduced in DotNetNuke 5 for adding tokens into a DotNetNuke skin. A Skin Object Token is a web user control, it covers skin elements such as the logo, menu, search, login links, date, copyright, languages, links, banners, privacy, terms of use etc. This new Object token method has been introduced into DotNetNuke with the idea of making it simpler to add a skin object into a DotNetNuke skin. The videos contain: Video 1 - Introduction to HTML Object Token Skinning Video 2 - Basic Styling of a Skin and Creating Multiple Content Panes Video 3 - Styling, Control Panel, Login and Register Skin Object Tokens Video 4 - Packaging, Installing, Testing and Viewing the ASCX Version of the Skin Video 5 - Viewing the Attributes for Skin Object Tokens, Logo Token, Search Token Video 6 - Breadcrumb Token, Text Token and Localization, Links Token Video 7 - More Skin Tokens and Token Replacement Video 8 - Demonstration of the Object Tokens and Bug Fixing Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • How do I call functions of an object inside the same object?

    - by Roly
    I have the following Javascript code add_num = { f: function(html, num) { alert(this.page); }, page : function() { return parseInt(this.gup('page')); }, gup : function(name) { name = name.replace(/[\[]/,'\\\[').replace(/[\]]/,'\\\]'); var regex = new RegExp('[\\?&]'+name+'=([^&#]*)'); var results = regex.exec(window.location.href); if(results == null) return ''; else return results[1]; } } But when I call add_num.f() what I get from alert() is the actual code of page. That is, it returns function() { return parseInt(this.gup('page')); } I was expecting a numeric value and not any code at all.

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  • empty() returning TRUE on object's non-empty property

    - by Michal M
    I've got a very weird and unexpected problem. empty() is returning TRUE on a non-empty property for a reason unknown to me. class MyObject { private $_property; public function __construct($property) { $this->_property = $property; } public function __get($name) { $priv_name = "_{$name}"; if (isset($this->$priv_name)) { return $this->$priv_name; } else { return NULL; } } } $obj = new MyObject('string value'); echo $obj->property; // Output 'string value' echo empty($obj->property); // Output 1 (means, that property is empty) Would this mean, that the __get() magic function is not called when using empty()? btw. I'm running PHP version 5.0.4

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  • How does pattern matching work behind the scenes in F#?

    - by kryptic
    Hello Everyone, I am completely new to F# (and functional programming in general) but I see pattern matching used everywhere in sample code. I am wondering for example how pattern matching actually works? For example, I imagine it working the same as a for loop in other languages and checking for matches on each item in a collection. This is probably far from correct, how does it actually work behind the scenes?

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  • How to convert an object into a double?

    - by george t.
    I am working on VS C# on the following code, which converts an user input math expression and computes it. MSScriptControl.ScriptControl sc = new MSScriptControl.ScriptControl(); sc.Language = "VBScript"; sc.ExecuteStatement( "function pi\n" + "pi = 3.14159265\n" + "end function"); sc.ExecuteStatement( "function e\n" + "e = exp(1)\n" + "end function"); expression = textBox1.Text.ToString(); expression = expression.Replace("x", i.ToString()); object y = sc.Eval(expression); string k = y.ToString(); double result = double.Parse(k); While this outputs onto the console with the correct result, I want to use the values to make a graph of the function user inputs and it's not doing it correctly. Thank you for your help.

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  • How to read a Choice Field from Sharepoint 2010 Client Object Model

    - by Eric
    Hello, I'm using Sharepoint 2010 Object Model. I'm trying to retrive the content of a Custom List. Everything works fine except if when I try to retrieve a Choice Field. When I try to retrieve the choice field, I got an PropertyOrFieldNotInitializedException exception... Here is the code I'm using: ClientContext clientContext = new ClientContext("https://mysite"); clientContext.FormsAuthenticationLoginInfo = new FormsAuthenticationLoginInfo("aaa", bbb"); clientContext.AuthenticationMode = ClientAuthenticationMode.FormsAuthentication; List list = clientContext.Web.Lists.GetByTitle("mylist"); CamlQuery camlQuery = new CamlQuery(); camlQuery.ViewXml = "<View/>"; ListItemCollection listItems = list.GetItems(camlQuery); clientContext.Load(listItems); clientContext.ExecuteQuery(); foreach (ListItem listItem in listItems) { listBoxControl1.Items.Add(listItem["Assigned_x0020_Company"]); } Thank you for you help! Eric

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  • Drop Down list null value not working for selected text c#?

    - by Tamara JQ
    Hi guys, Basically I have a drop down list which is populated with text and values depending on a selected index of a radio button list. The code is as follows: protected void RBLGender_SelectedIndexChanged(object sender, EventArgs e) { DDLTrous.Items.Clear(); DDLShoes.Items.Clear(); if (RBLGender.SelectedValue.Equals("Male")) { String[] MaleTrouserText = {"[N/A]", "28\"", "30\"", "32\"", "34\"", "36\"", "38\"", "40\"", "42\"", "44\"", "48\""}; String[] MaleTrouserValue = { null, "28\"", "30\"", "32\"", "34\"", "36\"", "38\"", "40\"", "42\"", "44\"", "48\"" }; String[] MaleShoeText = { "[N/A]", "38M", "39M", "40M", "41M", "42M", "43M", "44M", "45M", "46M", "47M" }; String[] MaleShoeValue = { null, "38M", "39M", "40M", "41M", "42M", "43M", "44M", "45M", "46M", "47M" }; for (int i = 0; i < MaleTrouserText.Length; i++) { ListItem MaleList = new ListItem(MaleTrouserText[i], MaleTrouserValue[i]); DDLTrous.Items.Add(MaleList); } for (int i = 0; i < MaleShoeText.Length; i++) { ListItem MaleShoeList = new ListItem(MaleShoeText[i], MaleShoeValue[i]); DDLShoes.Items.Add(MaleShoeList); } } else if (RBLGender.SelectedValue.Equals("Female"))` When the text '[N/A]' is selected I want the value NULL to be inserted into the database. At present when '[N/A]' is selected the value entered into the database is [N/A] does anyone know why? Thanks in advance.

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  • A C# implementation of the CallStream pattern

    - by Bertrand Le Roy
    Dusan published this interesting post a couple of weeks ago about a novel JavaScript chaining pattern: http://dbj.org/dbj/?p=514 It’s similar to many existing patterns, but the syntax is extraordinarily terse and it provides a new form of friction-free, plugin-less extensibility mechanism. Here’s a JavaScript example from Dusan’s post: CallStream("#container") (find, "div") (attr, "A", 1) (css, "color", "#fff") (logger); The interesting thing here is that the functions that are being passed as the first argument are arbitrary, they don’t need to be declared as plug-ins. Compare that with a rough jQuery equivalent that could look something like this: $.fn.logger = function () { /* ... */ } $("selector") .find("div") .attr("A", 1) .css("color", "#fff") .logger(); There is also the “each” method in jQuery that achieves something similar, but its syntax is a little more verbose. Of course, that this pattern can be expressed so easily in JavaScript owes everything to the extraordinary way functions are treated in that language, something Douglas Crockford called “the very best part of JavaScript”. One of the first things I thought while reading Dusan’s post was how I could adapt that to C#. After all, with Lambdas and delegates, C# also has its first-class functions. And sure enough, it works really really well. After about ten minutes, I was able to write this: CallStreamFactory.CallStream (p => Console.WriteLine("Yay!")) (Dump, DateTime.Now) (DumpFooAndBar, new { Foo = 42, Bar = "the answer" }) (p => Console.ReadKey()); Where the Dump function is: public static void Dump(object options) { Console.WriteLine(options.ToString()); } And DumpFooAndBar is: public static void DumpFooAndBar(dynamic options) { Console.WriteLine("Foo is {0} and bar is {1}.", options.Foo, options.Bar); } So how does this work? Well, it really is very simple. And not. Let’s say it’s not a lot of code, but if you’re like me you might need an Advil after that. First, I defined the signature of the CallStream method as follows: public delegate CallStream CallStream (Action<object> action, object options = null); The delegate define a call stream as something that takes an action (a function of the options) and an optional options object and that returns a delegate of its own type. Tricky, but that actually works, a delegate can return its own type. Then I wrote an implementation of that delegate that calls the action and returns itself: public static CallStream CallStream (Action<object> action, object options = null) { action(options); return CallStream; } Pretty nice, eh? Well, yes and no. What we are doing here is to execute a sequence of actions using an interesting novel syntax. But for this to be actually useful, you’d need to build a more specialized call stream factory that comes with some sort of context (like Dusan did in JavaScript). For example, you could write the following alternate delegate signature that takes a string and returns itself: public delegate StringCallStream StringCallStream(string message); And then write the following call stream (notice the currying): public static StringCallStream CreateDumpCallStream(string dumpPath) { StringCallStream str = null; var dump = File.AppendText(dumpPath); dump.AutoFlush = true; str = s => { dump.WriteLine(s); return str; }; return str; } (I know, I’m not closing that stream; sure; bad, bad Bertrand) Finally, here’s how you use it: CallStreamFactory.CreateDumpCallStream(@".\dump.txt") ("Wow, this really works.") (DateTime.Now.ToLongTimeString()) ("And that is all."); Next step would be to combine this contextual implementation with the one that takes an action parameter and do some really fun stuff. I’m only scratching the surface here. This pattern could reveal itself to be nothing more than a gratuitous mind-bender or there could be applications that we hardly suspect at this point. In any case, it’s a fun new construct. Or is this nothing new? You tell me… Comments are open :)

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  • EMBED vs. OBJECT

    - by JayhawksFan93
    Which is the right/best tag to use in my HTML file when I want to display the Adobe PDF viewer? Right now I'm using the code below, but there are weird side effects (e.g. it seems to steal the starting focus that I've set to another INPUT text box; it doesn't seem to play real well with the jQueryUI Resizeable class; etc.) <embed src="abc.pdf" type="application/pdf" /> Could I even do the same thing with the OBJECT tag? Are there advantages/disadvantages to using one tag vs. the other?

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  • Unable to cast object of type 'System.Object[]' to type 'System.String[]'

    - by salvationishere
    I am developing a C# VS 2008 / SQL Server website application. I am a newbie to ASP.NET. I am getting the above error, however, on the last line of the following code. Can you give me advice on how to fix this? This compiles correctly, but I encounter this error after running it. DataTable dt; Hashtable ht; string[] SingleRow; ... SqlConnection conn2 = new SqlConnection(connString); SqlCommand cmd = conn2.CreateCommand(); cmd.CommandText = "dbo.AppendDataCT"; cmd.Connection = conn2; SingleRow = (string[])dt.Rows[1].ItemArray; My error: System.InvalidCastException was caught Message="Unable to cast object of type 'System.Object[]' to type 'System.String[]'." Source="App_Code.g68pyuml" StackTrace: at ADONET_namespace.ADONET_methods.AppendDataCT(DataTable dt, Hashtable ht) in c:\Documents and Settings\Admin\My Documents\Visual Studio 2008\WebSites\Jerry\App_Code\ADONET methods.cs:line 88 InnerException:

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  • Design patterns frequently seen in embedded systems programming

    - by softwarelover
    I don't have any question related to coding. My concerns are about embedded systems programming independent of any particular programming language. Because I am new in the realm of embedded programming, I would quite appreciate responses from those who consider themselves experienced embedded systems programmers. I basically have 2 questions. Of the design patterns listed below are there any seen frequently in embedded systems programming? Abstraction-Occurrence pattern General Hierarchy pattern Player-Role pattern Singleton pattern Observer pattern Delegation pattern Adapter pattern Facade pattern Immutable pattern Read-Only Interface pattern Proxy pattern As an experienced embedded developer, what design patterns have you, as an individual, come across? There is no need to describe the details. Only the pattern names would suffice. Please share your own experience. I believe the answers to the above questions would work as a good starting point for any novice programmers in the embedded world.

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  • Runtime Error 424 Object Required

    - by Luis
    Hey so I get this error in this code: Private Sub Request_Stuff_button_Click() Call Main.createObjects Call My_Control.requestStuff End Sub at the 'Call My_Control.requestStuff' line. The 'Main' module looks like this: Public My_Control As ControlObject Public Sub createObjects() If My_Control Is Nothing Then Set My_Control = New ControlObject End If End Sub The weirdest thing is that when I add Dim x As Integer x = My_Control.dummyInt right before the line that gets me the error, x gets the correct value right before the error happens which means My_Control is definitely an object and is definitely not nothing. This error is killing me, thanks in advance.

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  • Can a WPF ComboBox display alternative text when its selection is null?

    - by Garth T Kidd
    G'day! I want my WPF ComboBox to display some alternative text when its data-bound selection is null. The view model has the expected properties: public ThingoSelectionViewModel : INotifyPropertyChanged { public ThingoSelectionViewModel(IProvideThingos) { this.Thingos = IProvideThingos.GetThingos(); } public ObservableCollection<Thingo> Thingos { get; set; } public Thingo SelectedThingo { get { return this.selectedThingo; } set { // set this.selectedThingo and raise the property change notification } // ... } The view has XAML binding to the view model in the expected way: <ComboBox x:Name="ComboboxDrive" SelectedItem="{Binding Path=SelectedThingo}" IsEditable="false" HorizontalAlignment="Left" MinWidth="100" IsReadOnly="false" Style="{StaticResource ComboboxStyle}" Grid.Column="1" Grid.Row="1" Margin="5" SelectedIndex="0"> <ComboBox.ItemsSource> <CompositeCollection> <ComboBoxItem IsEnabled="False">Select a thingo</ComboBoxItem> <CollectionContainer Collection="{Binding Source={StaticResource Thingos}}" /> </CompositeCollection> </ComboBox.ItemsSource> </ComboBox> The ComboBoxItem wedged into the top is a way to get an extra item at the top. It's pure chrome: the view model stays pure and simple. There's just one problem: the users want "Select a thingo" displayed whenever the ComboBox' selection is null. The users do not want a thingo selected by default. They want to see a message telling them to select a thingo. I'd like to avoid having to pollute the viewmodel with a ThingoWrapper class with a ToString method returning "Select a thingo" if its .ActualThingo property is null, wrapping each Thingo as I populate Thingos, and figuring out some way to prevent the user from selecting the nulled Thingo. Is there a way to display "Select a thingo" within the ComboBox' boundaries using pure XAML, or pure XAML and a few lines of code in the view's code-behind class?

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  • Getters and Setters are bad OO design?

    - by Dan
    Getters and Setters are bad Briefly reading over the above article I find that getters and setters are bad OO design and should be avoided as they go against Encapsulation and Data Hiding. As this is the case how can it be avoided when creating objects and how can one model objects to take this into account. In cases where a getter or setter is required what other alternatives can be used? Thanks.

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  • Improvements to Joshua Bloch's Builder Design Pattern?

    - by Jason Fotinatos
    Back in 2007, I read an article about Joshua Blochs take on the "builder pattern" and how it could be modified to improve the overuse of constructors and setters, especially when an object has a large number of properties, most of which are optional. A brief summary of this design pattern is articled here [http://rwhansen.blogspot.com/2007/07/theres-builder-pattern-that-joshua.html]. I liked the idea, and have been using it since. The problem with it, while it is very clean and nice to use from the client perspective, implementing it can be a pain in the bum! There are so many different places in the object where a single property is reference, and thus creating the object, and adding a new property takes a lot of time. So...I had an idea. First, an example object in Joshua Bloch's style: Josh Bloch Style: public class OptionsJoshBlochStyle { private final String option1; private final int option2; // ...other options here <<<< public String getOption1() { return option1; } public int getOption2() { return option2; } public static class Builder { private String option1; private int option2; // other options here <<<<< public Builder option1(String option1) { this.option1 = option1; return this; } public Builder option2(int option2) { this.option2 = option2; return this; } public OptionsJoshBlochStyle build() { return new OptionsJoshBlochStyle(this); } } private OptionsJoshBlochStyle(Builder builder) { this.option1 = builder.option1; this.option2 = builder.option2; // other options here <<<<<< } public static void main(String[] args) { OptionsJoshBlochStyle optionsVariation1 = new OptionsJoshBlochStyle.Builder().option1("firefox").option2(1).build(); OptionsJoshBlochStyle optionsVariation2 = new OptionsJoshBlochStyle.Builder().option1("chrome").option2(2).build(); } } Now my "improved" version: public class Options { // note that these are not final private String option1; private int option2; // ...other options here public String getOption1() { return option1; } public int getOption2() { return option2; } public static class Builder { private final Options options = new Options(); public Builder option1(String option1) { this.options.option1 = option1; return this; } public Builder option2(int option2) { this.options.option2 = option2; return this; } public Options build() { return options; } } private Options() { } public static void main(String[] args) { Options optionsVariation1 = new Options.Builder().option1("firefox").option2(1).build(); Options optionsVariation2 = new Options.Builder().option1("chrome").option2(2).build(); } } As you can see in my "improved version", there are 2 less places in which we need to add code about any addition properties (or options, in this case)! The only negative that I can see is that the instance variables of the outer class are not able to be final. But, the class is still immutable without this. Is there really any downside to this improvement in maintainability? There has to be a reason which he repeated the properties within the nested class that I'm not seeing?

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  • How to map IEnumerable<SelectListItem> to IList<> for ListBox

    - by Superhuman
    I have two classes. Class1 and Class2. public class Class1{ ... public virtual IList<Class2> Class2s{get;set;} ... } public class Class2{ ... public virtual IList<Class1> Class1s{get;set;} ... } The view contains <%=Html.ListBox("Class2s", ViewData.Model.Class2s.Select( x => new SelectListItem { Text = x.Name, Value = x.Id.ToString(), Selected = ViewData.Model.Class1.Class2s.Any(y => y.Id == x.Id) }) They have many to many mapping. I have a ListBox in Class1 view which displays Class2. How to map the output of the ListBox back to IList Class2s property of Class1? I am able to display the values in the ListBox but unable to map back the SelectListItem to IList.

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  • Builder Pattern: When to fail?

    - by skiwi
    When implementing the Builder Pattern, I often find myself confused with when to let building fail and I even manage to take different stands on the matter every few days. First some explanation: With failing early I mean that building an object should fail as soon as an invalid parameter is passed in. So inside the SomeObjectBuilder. With failing late I mean that building an object only can fail on the build() call that implicitely calls a constructor of the object to be built. Then some arguments: In favor of failing late: A builder class should be no more than a class that simply holds values. Moreover, it leads to less code duplication. In favor of failing early: A general approach in software programming is that you want to detect issues as early as possible and therefore the most logical place to check would be in the builder class' constructor, 'setters' and ultimately in the build method. What is the general concensus about this?

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  • NHibernate Query object collection issue

    - by Mahesh
    Hi, I am new to NHibernate and need some information regarding the internal working of the engine: I have a table called Student and the design is as follows: RollNo Name City Postcode and there are 5 more columns like this. I have School class and mappings associated with it. I am querying RollNo and Name using session as given below: IQuery query = session.CreateQuery("SELECT RollNo,Name FROM Student); Executing query.List resulting in error because the query is returning object[][]. Now, I changed the query as given below: IQuery query = session.CreateQuery("FROM Student); Executing query.List on this query yeilds the desired results. But, the results contain more data than I want. Could you please let me know the query to which I can get RollNo and Name from Student and castable as Student collection. Thanks, Mahesh

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  • What is the difference between JSON and Object Literal Notation?

    - by burak ozdogan
    Hi, Can someone tell me what is the main difference between a Javascript object defined by using "Object Literal Notation" and JSON object? According to a Javascript book it says this is an object defined by using Object Notation: var newObject = { prop1 : true, showMessage : function (msg) {alert(msg)} }; Why it is not a JSON object in this case? Just because it is not defined by using quotation marks? Thanks,

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  • wpf c# databinding on object

    - by Enriquev
    Hello, say I have this control: public partial class bloc999 : UserControl { bloc999Data mainBlock = new bloc999Data(); public bloc999() { InitializeComponent(); mainBlock.txtContents = "100"; base.DataContext = mainBlock; } } in the xaml: <TextBox Margin="74,116,106,0" Name="txtContents" Text="{Binding Path=txtContents, UpdateSourceTrigger=PropertyChanged,Mode = TwoWay}" /> <TextBox Margin="74,145,106,132" Name="txtContents2" Text="{Binding Path=txtContents2, UpdateSourceTrigger=PropertyChanged,Mode = TwoWay}" /> Then I have this class: public class bloc999Data : INotifyPropertyChanged { string _txtContents; string _txtContents2; public event PropertyChangedEventHandler PropertyChanged; void NotifyPropertyChanged(string propName) { if (this.PropertyChanged != null) this.PropertyChanged( this, new PropertyChangedEventArgs(propName)); } public string txtContents2 { get { return this._txtContents2; } set { if (int.Parse(value) > int.Parse(this._txtContents)) { this._txtContents2 = "000"; } else this._txtContents2 = value; NotifyPropertyChanged("txtContents2"); } } public string txtContents { get { return this._txtContents; } set { this._txtContents = value; NotifyPropertyChanged("txtContents"); } } } Ok now say I have A button on the form and I do this in the code: mainBlock.txtContents2 = "7777777"; It puts 000 in the textbox, but If i just type in manually, in the textbox (txtContents2, the setter code is called but for some reason the textboxes value does not change, the instance value does change. help?

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  • Design Pattern for Complex Data Modeling

    - by Aaron Hayman
    I'm developing a program that has a SQL database as a backing store. As a very broad description, the program itself allows a user to generate records in any number of user-defined tables and make connections between them. As for specs: Any record generated must be able to be connected to any other record in any other user table (excluding itself...the record, not the table). These "connections" are directional, and the list of connections a record has is user ordered. Moreover, a record must "know" of connections made from it to others as well as connections made to it from others. The connections are kind of the point of this program, so there is a strong possibility that the number of connections made is very high, especially if the user is using the software as intended. A record's field can also include aggregate information from it's connections (like obtaining average, sum, etc) that must be updated on change from another record it's connected to. To conserve memory, only relevant information must be loaded at any one time (can't load the entire database in memory at load and go from there). I cannot assume the backing store is local. Right now it is, but eventually this program will include syncing to a remote db. Neither the user tables, connections or records are known at design time as they are user generated. I've spent a lot of time trying to figure out how to design the backing store and the object model to best fit these specs. In my first design attempt on this, I had one object managing all a table's records and connections. I attempted this first because it kept the memory footprint smaller (records and connections were simple dicts), but maintaining aggregate and link information between tables became....onerous (ie...a huge spaghettified mess). Tracing dependencies using this method almost became impossible. Instead, I've settled on a distributed graph model where each record and connection is 'aware' of what's around it by managing it own data and connections to other records. Doing this increases my memory footprint but also let me create a faulting system so connections/records aren't loaded into memory until they're needed. It's also much easier to code: trace dependencies, eliminate cycling recursive updates, etc. My biggest problem is storing/loading the connections. I'm not happy with any of my current solutions/ideas so I wanted to ask and see if anybody else has any ideas of how this should be structured. Connections are fairly simple. They contain: fromRecordID, fromTableID, fromRecordOrder, toRecordID, toTableID, toRecordOrder. Here's what I've come up with so far: Store all the connections in one big table. If I do this, either I load all connections at once (one big db call) or make a call every time a user table is loaded. The big issue here: the size of the connections table has the potential to be huge, and I'm afraid it would slow things down. Store in separate tables all the outgoing connections for each user table. This is probably the worst idea I've had. Now my connections are 'spread out' over multiple tables (one for each user table), which means I have to make a separate DB called to each table (or make a huge join) just to find all the incoming connections for a particular user table. I've avoided making "one big ass table", but I'm not sure the cost is worth it. Store in separate tables all outgoing AND incoming connections for each user table (using a flag to distinguish between incoming vs outgoing). This is the idea I'm leaning towards, but it will essentially double the total DB storage for all the connections (as each connection will be stored in two tables). It also means I have to make sure connection information is kept in sync in both places. This is obviously not ideal but it does mean that when I load a user table, I only need to load one 'connection' table and have all the information I need. This also presents a separate problem, that of connection object creation. Since each user table has a list of all connections, there are two opportunities for a connection object to be made. However, connections objects (designed to facilitate communication between records) should only be created once. This means I'll have to devise a common caching/factory object to make sure only one connection object is made per connection. Does anybody have any ideas of a better way to do this? Once I've committed to a particular design pattern I'm pretty much stuck with it, so I want to make sure I've come up with the best one possible.

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  • Matching the superclass's constructor's parameter list, is treating a null default value as a non-null value within a constructor a violation of LSP?

    - by Panzercrisis
    I kind of ran into this when messing around with FlashPunk, and I'm going to use it as an example. Essentially the main sprite class is pretty much class Entity. Entity's constructor has four parameters, each with a default value. One of them is graphic, whose default value is null. Entity is designed to be inherited from, with many such subclasses providing their own graphic within their own internal workings. Normally these subclasses would not have graphic in their constructor's parameter lists, but would simply pick something internally and go with it. However I was looking into possibly still adhering to the Liskov Substitution Principal. Which led me to the following example: package com.blank.graphics { import net.flashpunk.*; import net.flashpunk.graphics.Image; public class SpaceGraphic extends Entity { [Embed(source = "../../../../../../assets/spaces/blank.png")] private const BLANK_SPACE:Class; public function SpaceGraphic(x:Number = 0, y:Number = 0, graphic:Graphic = null, mask:Mask = null) { super(x, y, graphic, mask); if (!graphic) { this.graphic = new Image(BLANK_SPACE); } } } } Alright, so now there's a parameter list in the constructor that perfectly matches the one in the super class's constructor. But if the default value for graphic is used, it'll exhibit two different behaviors, depending on whether you're using the subclass or the superclass. In the superclass, there won't be a graphic, but in the subclass, it'll choose the default graphic. Is this a violation of the Liskov Substitution Principal? Does the fact that subclasses are almost intended to use different parameter lists have any bearing on this? Would minimizing the parameter list violate it in a case like this? Thanks.

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  • Object tree navigation language in Java

    - by lewap
    In the system which I'm currently developing I often have to navigate an object tree and based on its state and values take actions. In normal Java this results in tedious for loops, if statements etc... Are there alternative ways to achieve tree navigation, similar to XPath for XML? I know there is JXPath and OGNL, but do you know any other libraries for such purpose? Do you know any libraries which generate bytecodes for specific tree navigation expressions to make the processing as fast as Java native fors and ifs?

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