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• WCF: Per-Call and Per-Session services...need convincing that Per-Call is worthwhile

  - by mrlane

  Hello all. We are currently doing a review of our WCF service design and one thing that is bothering me is the decision between Per-Call and Per-Session services. I believe I understand the concept behind both, but I am not really seeing the advantage of Per-Call services. I understand that the motivation for using Per-Call services is that a WCF services only holds a servier object for the life of a call thereby restricting the time that an expensive resource is held by the service instance, but to me its much simpler to use the more OO like Per-Session model where your proxy object instance always corrisponds to the same server object instance and just handle any expensive resources manually. For example, say I have a CRUD Service with Add, Update, Delete, Select methods on it. This could be done as a Per-Call service with database connection (the "expensive resource") instanciated in the server object constructor. Alternately it could be a Per-Session service with a database connection instanciated and closed within each CRUD method exposed. To me it is no different resource wise and it makes the programming model simpler as the client can be assured that they always have the same server object for their proxies: any in-expensive state that there may be between calls is maintained and no extra parameters are needed on methods to identify what state data must be retrieved by the service when it is instanciating a new server object again (as in the case of Per-Call). Its just like using classes and objects, where the same resource management issues apply, but we dont create new object instances for each method call we have on an object! So what am I missing with the Per-Call model? Thanks

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• WPF designer gives exception when databinding a label to a checkbox

  - by John

  I'm sure it's something stupid, but I'm playing around with databinding. I have a checkbox and a label on a form. What I'm trying to do is simply bind the Content of the label to the checkbox's IsChecked value. What I've done runs fine (no compilation errors and acts as expected), but if I touch the label in the XAML, the designer trows an exception: System.NullReferenceException Object reference not set to an instance of an object. at MS.Internal.Designer.PropertyEditing.Editors.MarkupExtensionInlineEditorControl.BuildBindingString(Boolean modeSupported, PropertyEntry propertyEntry) at <Window x:Class="UnitTestHelper.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:FileSysCtls="clr-namespace:WPFFileSystemUserControls;assembly=WPFFileSystemUserControls" xmlns:HelperClasses="clr-namespace:UnitTestHelper" Title="MainWindow" Height="406" Width="531"> <Window.Resources> <HelperClasses:ThreestateToBinary x:Key="CheckConverter" /> </Window.Resources> <Grid Height="367" Width="509"> <CheckBox Content="Step into subfolders" Height="16" HorizontalAlignment="Left" Margin="17,254,0,0" Name="chkSubfolders" VerticalAlignment="Top" Width="130" IsThreeState="False" /> <Label Height="28" HorizontalAlignment="Left" Margin="376,254,0,0" Name="lblStepResult" VerticalAlignment="Top" Width="120" IsEnabled="True" Content="{Binding IsChecked, ElementName=chkSubfolders, Mode=OneWay, UpdateSourceTrigger=PropertyChanged, Converter={StaticResource CheckConverter}}" /> </Grid> The ThreeStateToBinary class is as follows: class ThreestateToBinary : IValueConverter { #region IValueConverter Members public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) { if ((bool)value) return "Checked"; else return "Not checked"; //throw new NotImplementedException(); } public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) { return ((string)value == "Checked"); //throw new NotImplementedException(); } #endregion } Quite honestly, I'm playing around with it at this point. It was originally simpler (not using the ValueConverter) but was displaying similar behavior when I simply had the content set to: Content="{Binding IsChecked, ElementName=chkSubfolders, UpdateSourceTrigger=PropertyChanged}" Any ideas? Thanks, John

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• Inconsistency in passing objects from VBA to .NET via COM

  - by Akash

  I have the following interface defined to expose a .NET class to COM: [InterfaceType(ComInterfaceType.InterfaceIsDual)] [Guid("6A983BCC-5C83-4b30-8400-690763939659")] [ComVisible(true)] public interface IComClass { object Value { get; set; } object GetValue(); void SetValue(object value); } The implementation of this interface is trivial: [ClassInterface(ClassInterfaceType.None)] [Guid("66D0490F-718A-4722-8425-606A6C999B82")] [ComVisible(true)] public class ComClass : IComClass { private object _value = 123.456; public object Value { get { return this._value; } set { this._value = value; } } public object GetValue() { return this._value; } public void SetValue(object value) { this._value = value; } } I have then registered this using RegAsm, and tried to call it from Excel via the following code: Public Sub ComInterop() Dim cc As ComClass Set cc = New ComClass cc.SetValue (555.555) valueByGetter = cc.GetValue valueByProperty = cc.Value cc.Value = 555.555 End Sub When I step throught this code, valueByGetter = 555.5555 and valueByProperty = 555.555 as expected. However, I get an "Object required" runtime error on the final line. Why does setting the value via the setter method work but setting via the property fail? What do I have to change to get the property to work as expected?

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• TCL TDom: Looping through Objects

  - by pws5068

  Using TDom, I would like to cycle through a list of objects in the following format: <object> <type>Hardware</type> <name>System Name</name> <description>Basic Description of System.</description> <attributes> <vendor>Dell</vendor> <contract>MM/DD/YY</contract> <supportExpiration>MM/DD/YY</supportExpiration> <location>Building 123</location> <serial>xxx-xxx-xxxx</serial> <mac>some-mac-address</mac> </attributes> </object> <object> <type>Software</type> <name>Second Object</name> ... Then I use TDom to make a list of objects: set dom [dom parse $xml] set doc [$dom documentElement] set nodeList [$doc selectNodes /systems/object] So far I've done this to (theoretically) select every "Object" node from the list. How can I loop through them? Is it just: foreach node $nodeList { For each object, I need to retrieve the association of each attribute. From the example, I need to remember that the "name" is "System Name", "vendor" is "Dell", etc. I'm new to TCL but in other languages I would use an object or an associative list to store these. Is this possible? Can you show me an example of the syntax to select an attribute in this manner?

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• Moving to .net 4 results in System.Transactions Critical: 0

  - by john

  Hi I have fully working project in .net 3.5SP1, with EF 1 ORM. I tried to upgrade to .net 4. No issue while upgrading... Then i ran the project and got a NullExecptionError, with no stack trace... and no way to debug. Looking at the output windows i can read this: System.Transactions Critical: 0 : <TraceRecord xmlns="http://schemas.microsoft.com/2004/10/E2ETraceEvent/TraceRecord" Severity="Critical"><TraceIdentifier>http://msdn.microsoft.com/TraceCodes/System/ActivityTracing/2004/07/Reliability/Exception/Unhandled</TraceIdentifier><Description>Unhandled exception</Description><AppDomain>OTCSouscriptions.vshost.exe</AppDomain><Exception><ExceptionType>System.NullReferenceException, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</ExceptionType><Message>Object reference not set to an instance of an object.</Message><StackTrace> at System.Windows.StyleHelper.GetInstanceValue(UncommonField`1 dataField, DependencyObject container, FrameworkElement feChild, FrameworkContentElement fceChild, Int32 childIndex, DependencyProperty dp, Int32 i, EffectiveValueEntry&amp;amp; entry) at System.Windows.FrameworkTemplate.ReceivePropertySet(Object targetObject, XamlMember member, Object value, DependencyObject templatedParent) at System.Windows.FrameworkTemplate.&amp;lt;&amp;gt;c__DisplayClass6.&amp;lt;LoadOptimizedTemplateContent&amp;gt;b__4(Object sender, XamlSetValueEventArgs setArgs) at System.Xaml.XamlObjectWriter.OnSetValue(Object eventSender, XamlMember member, Object value) at System.Xaml.XamlObjectWriter.Logic_ApplyPropertyValue(ObjectWriterContext ctx, XamlMember prop, Object value, Boolean onParent) at System.Xaml.XamlObjectWriter.Logic_DoAssignmentToParentProperty(ObjectWriterContext ctx) at System.Xaml.XamlObjectWriter.Logic_AssignProvidedValue(ObjectWriterContext ctx) at System.Xaml.XamlObjectWriter.WriteEndObject() at System.Xaml.XamlWriter.WriteNode(XamlReader reader) at System.Windows.FrameworkTemplate.LoadTemplateXaml(XamlReader templateReader, XamlObjectWriter currentWriter) Any help appreciated... Thanks John

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• How do I copy or move an NSManagedObject from one context to another?

  - by Aeonaut

  I have what I assume is a fairly standard setup, with one scratchpad MOC which is never saved (containing a bunch of objects downloaded from the web) and another permanent MOC which persists objects. When the user selects an object from scratchMOC to add to her library, I want to either 1) remove the object from scratchMOC and insert into permanentMOC, or 2) copy the object into permanentMOC. The Core Data FAQ says I can copy an object like this: NSManagedObjectID *objectID = [managedObject objectID]; NSManagedObject *copy = [context2 objectWithID:objectID]; (In this case, context2 would be permanentMOC.) However, when I do this, the copied object is faulted; the data is initially unresolved. When it does get resolved, later, all of the values are nil; none of the data (attributes or relationships) from the original managedObject are actually copied or referenced. Therefore I can't see any difference between using this objectWithID: method and just inserting an entirely new object into permanentMOC using insertNewObjectForEntityForName:. I realize I can create a new object in permanentMOC and manually copy each key-value pair from the old object, but I'm not very happy with that solution. (I have a number of different managed objects for which I have this problem, so I don't want to have to write and update copy: methods for all of them as I continue developing.) Is there a better way?

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• Javascript: prototypal inheritance and the prototype property

  - by JanD

  Hi, I have a simple code fragment in JS working with prototype inheritance. function object(o) { function F() {} F.prototype = o; return new F(); } //the following code block has a alternate version var mammal = { color: "brown", getColor: function() { return this.color; } } var myCat = object(mammal); myCat.meow = function(){return "meow";} that worked fine but adding this: mammal.prototype.kindOf = "predator"; does not. ("mammal.prototype is undefined") Since I guessed that object maybe have no prototype I rewrote it, replacing the var mammal={... block with: function mammal() { this.color = "brown"; this.getColor = function() { return this.color; } } which gave me a bunch of other errors: "Function.prototype.toString called on incompatible object" and if I try to call _myCat.getColor() "myCat.getColor is not a function" Now I am totally confused. After reading Crockford, and Flanagan I did not get the solution for the errors. So it would be great if somebody knows... - why is the prototype undefined in the first example (which is foremost concern; I thought the prototype of explicitly set in the object() function) - why get I these strange errors trying to use the mammal function as prototype object in the object() function? Edit by the Creator of the Question: These two links helped a lot too: Prototypes_in_JavaScript on the spheredev wiki explains the way the prototype property works relativily simple. What it lacks is some try-out code examples. Some good examples are provided by Morris John's Article. I personally find the explanations are not that easy as in the first link, but still very good. The most difficult part even after I actually got it is really not to confuse the .prototype propery with the internal [[Prototype]] of an object.

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• Business Objects - Containers or functional?

  - by Walter

  Where I work, we've gone back and forth on this subject a number of times and are looking for a sanity check. Here's the question: Should Business Objects be data containers (more like DTOs) or should they also contain logic that can perform some functionality on that object. Example - Take a customer object, it probably contains some common properties (Name, Id, etc), should that customer object also include functions (Save, Calc, etc.)? One line of reasoning says separate the object from the functionality (single responsibility principal) and put the functionality in a Business Logic layer or object. The other line of reasoning says, no, if I have a customer object I just want to call Customer.Save and be done with it. Why do I need to know about how to save a customer if I'm consuming the object? Our last two projects have had the objects separated from the functionality, but the debate has been raised again on a new project. Which makes more sense? EDIT These results are very similar to our debates. One vote to one side or another completely changes the direction. Does anyone else want to add their 2 cents? EDIT Eventhough the answer sampling is small, it appears that the majority believe that functionality in a business object is acceptable as long as it is simple but persistence is best placed in a separate class/layer. We'll give this a try. Thanks for everyone's input...

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• Java: Is clone() really ever used? What about defensive copying in getters/setters?

  - by GreenieMeanie

  Do people practically ever use defensive getters/setters? To me, 99% of the time you intend for the object you set in another object to be a copy of the same object reference, and you intend for changes you make to it to also be made in the object it was set in. If you setDate(Date dt) and modify dt later, who cares? Unless I want some basic immutable data bean that just has primitives and maybe something simple like a Date, I never use it. As far as clone, there are issues as to how deep or shallow the copy is, so it seems kind of "dangerous" to know what is going to come out when you clone an Object. I think I have only used clone() once or twice, and that was to copy the current state of the object because another thread (ie another HTTP request accessing the same object in Session) could be modifying it. Edit - A comment I made below is more the question: But then again, you DID change the Date, so it's kind of your own fault, hence whole discussion of term "defensive". If it is all application code under your own control among a small to medium group of developers, will just documenting your classes suffice as an alternative to making object copies? Or is this not necessary, since you should always assume something ISN'T copied when calling a setter/getter?

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• Button Visibility Converter

  - by developer

  Hi All, I have a requirement wherein I need to display on a User form, a Create Button if that user has doesnt have a profile and a Edit Button if he does have a profile. I am using a converter to change the visibility of the button. Below is my code, <StackPanel Orientation="Horizontal"> <Button Content="Create Profile" Visibility="{Binding Profile,Converter={StaticResource ButtonVisibilityConverter}, ConverterParameter='Create'}" Command="local:LaunchEditor" CommandParameter="{Binding}"/> <Button Content="Edit Profile" Visibility="{Binding Profile,Converter={StaticResource ButtonVisibilityConverter}, ConverterParameter='Edit'}" Command="local:LaunchEditor" CommandParameter="{Binding}"/> </StackPanel> Below is my converter code public class ButtonVisibilityConverter : IValueConverter { public object Convert(object value, Type targetType, object parameter, CultureInfo culture) { string btName = null; btName = (string)parameter; if ((value==null)&&(btName=="Create")) { return Visibility.Visible; } else if ((value != null) && (btName=="Edit")) { return Visibility.Visible; } else { return Visibility.Collapsed; } } public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) { throw new NotImplementedException(); } } Everything works fine initially, but the moment I click on the Create Profile window, and it is the constructor that loads the profile window, after that even if I close that window without doing anything, the Create button turns to edit. My guess is that, it is because the constructor would have create the profile object and so even though the object is empty it shows me edit button instead of create. Is there any other way I could display button visibility??

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• JPA2 Criteria API creates invalid SQL when using groupBy

  - by Stephan

  JPA2 with the Criteria API seems to generate invalid SQL for PostgreSQL. For this code: Root<DBObjectAccessCounter> from = query.from(DBObjectAccessCounter.class); Path<DBObject> object = from.get(DBObjectAccessCounter_.object); Expression<Long> sum = builder.sumAsLong(from.get(DBObjectAccessCounter_.count)); query.multiselect(object, sum).groupBy(object); I get the following exception: ERROR: column "dbobject1_.id" must appear in the GROUP BY clause or be used in an aggregate function The generated SQL is: select dbobjectac0_.object_id as col_0_0_, sum(dbobjectac0_.count) as col_1_0_, dbobject1_.id as id1001_, dbobject1_.name as name1013_, dbobject1_.lastChanged as lastChan2_1013_, dbobject1_.type_id as type3_1013_ from DBObjectAccessCounter dbobjectac0_ inner join DBObject dbobject1_ on dbobjectac0_.object_id=dbobject1_.id group by dbobjectac0_.object_id Obviously, the first item of the select statement (dbobjectac0_.object_id) does not match the group by clause. Simplified example It does not even work for this simple example: Root<DBObjectAccessCounter> from = query.from(DBObjectAccessCounter.class); Path<DBObject> object = from.get(DBObjectAccessCounter_.object); query.select(object).groupBy(object); which returns select dbobject1_.id as id924_, dbobject1_.name as name933_, dbobject1_.lastChanged as lastChan2_933_, dbobject1_.type_id as type3_933_ from DBObjectAccessCounter dbobjectac0_ inner join DBObject dbobject1_ on dbobjectac0_.object_id=dbobject1_.id group by dbobjectac0_.object_id Does anyone know how to fix this?

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• Resolve php "deadlock"

  - by Matt

  Hey all, I'm currently running into a situation that I guess would be called deadlock. I'm implementing a message service that calls various object methods.. it's quite similar to observer pattern.. Here's whats going on: Dispatcher.php Dispatcher.php <? class Dispatcher { ... public function message($name, $method) { // Find the object based on the name $object = $this->findObjectByName($name); // Slight psuedocode.. for ease of example if($this->not_initialized($object)) $object = new $object(); // This is where it locks up. } return $object->$method(); ... } class A { function __construct() { $Dispatcher->message("B", "getName"); } public function getName() { return "Class A"; } } class B { function __construct() { // Assume $Dispatcher is the classes $Dispatcher->message("A", "getName"); } public function getName() { return "Class B"; } } ?> It locks up when neither object is initialized. It just goes back and forth from message each other and no one can be initialized. Any help would be immensely helpful.. Thanks! Matt Mueller

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• Resolve php endless recursion issue

  - by Matt

  Hey all, I'm currently running into an endless recursion situation. I'm implementing a message service that calls various object methods.. it's quite similar to observer pattern.. Here's whats going on: Dispatcher.php class Dispatcher { ... public function message($name, $method) { // Find the object based on the name $object = $this->findObjectByName($name); // Slight psuedocode.. for ease of example if($this->not_initialized($object)) $object = new $object(); // This is where it locks up. } return $object->$method(); ... } class A { function __construct() { $Dispatcher->message("B", "getName"); } public function getName() { return "Class A"; } } class B { function __construct() { // Assume $Dispatcher is the classes $Dispatcher->message("A", "getName"); } public function getName() { return "Class B"; } } It locks up when neither object is initialized. It just goes back and forth from message each other and no one can be initialized. I'm looking for some kind of queue implementation that will make messages wait for each other.. One where the return values still get set. I'm looking to have as little boilerplate code in class A and class B as possible Any help would be immensely helpful.. Thanks! Matt Mueller

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• Generic property- specify the type at runtime

  - by Lirik

  I was reading a question on making a generic property, but I'm a little confused at by the last example from the first answer (I've included the relevant code below): You have to know the type at compile time. If you don't know the type at compile time then you must be storing it in an object, in which case you can add the following property to the Foo class: public object ConvertedValue { get { return Convert.ChangeType(Value, Type); } } That's seems strange: it's converting the value to the specified type, but it's returning it as an object when the value was stored as an object. Doesn't the returned object still require un-boxing? If it does, then why bother with the conversion of the type? I'm also trying to make a generic property whose type will be determined at run time: public class Foo { object Value {get;set;} Type ValType{get;set;} Foo(object value, Type type) { Value = value; ValType = type; } // I need a property that is actually // returned as the specified value type... public object ConvertedValue { get { return Convert.ChangeType(Value, ValType); } } } Is it possible to make a generic property? Does the return property still require unboxing after it's accessed?

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• How to highlight the new created file in JTree

  - by newbie123

  I want to make it like when I click a button, it will create a new file. Then the jTree will highlight the new file. Below are my code. Currently I create new file, i will show the new file but no highlight the file. class FileTreeModel implements TreeModel { private FileNode root; public FileTreeModel(String directory) { root = new FileNode(directory); } public Object getRoot() { return root; } public Object getChild(Object parent, int index) { FileNode parentNode = (FileNode) parent; return new FileNode(parentNode, parentNode.listFiles()[index].getName()); } public int getChildCount(Object parent) { FileNode parentNode = (FileNode) parent; if (parent == null || !parentNode.isDirectory() || parentNode.listFiles() == null) { return 0; } return parentNode.listFiles().length; } public boolean isLeaf(Object node) { return (getChildCount(node) == 0); } public int getIndexOfChild(Object parent, Object child) { FileNode parentNode = (FileNode) parent; FileNode childNode = (FileNode) child; return Arrays.asList(parentNode.list()).indexOf(childNode.getName()); } public void valueForPathChanged(TreePath path, Object newValue) { } public void addTreeModelListener(TreeModelListener l) { } public void removeTreeModelListener(TreeModelListener l) { } } class FileNode extends java.io.File { public FileNode(String directory) { super(directory); } public FileNode(FileNode parent, String child) { super(parent, child); } @Override public String toString() { return getName(); } } jTree = new JTree(); jTree.setBounds(new Rectangle(164, 66, 180, 421)); jTree.setBackground(SystemColor.inactiveCaptionBorder); jTree.setBorder(BorderFactory.createTitledBorder(null, "", TitledBorder.LEADING, TitledBorder.TOP, new Font("Arial", Font.BOLD, 12), new Color(0, 0, 0))); FileTreeModel model = new FileTreeModel(root); jTree.setRootVisible(false); jTree.setModel(model); expandAll(jTree); public void expandAll(JTree tree) { int row = 0; while (row < tree.getRowCount()) { tree.expandRow(row); row++; } }

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• Wildcards vs. generic methods

  - by FredOverflow

  Is there any practical difference between the following approaches to print all elements in a range? public static void printA(Iterable<?> range) { for (Object o : range) { System.out.println(o); } } public static <T> void printB(Iterable<T> range) { for (T x : range) { System.out.println(x); } } Apparently, printB involves an additional checked cast to Object (see line 16), which seems rather stupid to me -- isn't everything an Object anyway? public static void printA(java.lang.Iterable); Code: 0: aload_0 1: invokeinterface #18, 1; //InterfaceMethod java/lang/Iterable.iterator:()Ljava/util/Iterator; 6: astore_2 7: goto 24 10: aload_2 11: invokeinterface #24, 1; //InterfaceMethod java/util/Iterator.next:()Ljava/lang/Object; 16: astore_1 17: getstatic #30; //Field java/lang/System.out:Ljava/io/PrintStream; 20: aload_1 21: invokevirtual #36; //Method java/io/PrintStream.println:(Ljava/lang/Object;)V 24: aload_2 25: invokeinterface #42, 1; //InterfaceMethod java/util/Iterator.hasNext:()Z 30: ifne 10 33: return public static void printB(java.lang.Iterable); Code: 0: aload_0 1: invokeinterface #18, 1; //InterfaceMethod java/lang/Iterable.iterator:()Ljava/util/Iterator; 6: astore_2 7: goto 27 10: aload_2 11: invokeinterface #24, 1; //InterfaceMethod java/util/Iterator.next:()Ljava/lang/Object; 16: checkcast #3; //class java/lang/Object 19: astore_1 20: getstatic #30; //Field java/lang/System.out:Ljava/io/PrintStream; 23: aload_1 24: invokevirtual #36; //Method java/io/PrintStream.println:(Ljava/lang/Object;)V 27: aload_2 28: invokeinterface #42, 1; //InterfaceMethod java/util/Iterator.hasNext:()Z 33: ifne 10 36: return

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• Java Constructor Style (Check parameters aren't null)

  - by Peter

  What are the best practices if you have a class which accepts some parameters but none of them are allowed to be null? The following is obvious but the exception is a little unspecific: public class SomeClass { public SomeClass(Object one, Object two) { if (one == null || two == null) { throw new IllegalArgumentException("Parameters can't be null"); } //... } } Here the exceptions let you know which parameter is null, but the constructor is now pretty ugly: public class SomeClass { public SomeClass(Object one, Object two) { if (one == null) { throw new IllegalArgumentException("one can't be null"); } if (two == null) { throw new IllegalArgumentException("two can't be null"); } //... } Here the constructor is neater, but now the constructor code isn't really in the constructor: public class SomeClass { public SomeClass(Object one, Object two) { setOne(one); setTwo(two); } public void setOne(Object one) { if (one == null) { throw new IllegalArgumentException("one can't be null"); } //... } public void setTwo(Object two) { if (two == null) { throw new IllegalArgumentException("two can't be null"); } //... } } Which of these styles is best? Or is there an alternative which is more widely accepted? Cheers, Pete

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• C++ Namespaces & templates question

  - by Kotti

  Hi! I have some functions that can be grouped together, but don't belong to some object / entity and therefore can't be treated as methods. So, basically in this situation I would create a new namespace and put the definitions in a header file, the implementation in cpp file. Also (if needed) I would create an anonymous namespace in that cpp file and put all additional functions that don't have to be exposed / included to my namespace's interface there. See the code below (probably not the best example and could be done better with another program architecture, but I just can't think of a better sample...) Sample code (header) namespace algorithm { void HandleCollision(Object* object1, Object* object2); } Sample code (cpp) #include "header" // Anonymous namespace that wraps // routines that are used inside 'algorithm' methods // but don't have to be exposed namespace { void RefractObject(Object* object1) { // Do something with that object // (...) } } namespace algorithm { void HandleCollision(Object* object1, Object* object2) { if (...) RefractObject(object1); } } So far so good. I guess this is a good way to manage my code, but I don't know what should I do if I have some template-based functions and want to do basically the same. If I'm using templates, I have to put all my code in the header file. Ok, but how should I conceal some implementation details then? Like, I want to hide RefractObject function from my interface, but I can't simply remove it's declaration (just because I have all my code in a header file)... The only approach I came up with was something like: Sample code (header) namespace algorithm { // Is still exposed as a part of interface! namespace impl { template <typename T> void RefractObject(T* object1) { // Do something with that object // (...) } } template <typename T, typename Y> void HandleCollision(T* object1, Y* object2) { impl::RefractObject(object1); // Another stuff } } Any ideas how to make this better in terms of code designing?

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• Can I have two names for the same variable?

  - by Roman

  The short version of the question: I do: x = y. Then I change x, and y is unchanged. What I want is to "bind" x and y in such a way that I change y whenever I change x. The extended version (with some details): I wrote a class ("first" class) which generates objects of another class ("second" class). In more details, every object of the second class has a name as a unique identifier. I call a static method of the first class with a name of the object from the second class. The first class checks if such an object was already generated (if it is present in the static HashMap of the first class). If it is already there, it is returned. If it is not yet there, it is created, added to the HashMap and returned. And then I have the following problem. At some stage of my program, I take an object with a specific name from the HashMap of the first class. I do something with this object (for example change values of some fields). But the object in the HashMap does not see these changes! So, in fact, I do not "take" an object from the HashMap, I "create a copy" of this object and this is what I would like to avoid.

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• Why does this code sample produce a memory leak?

  - by citronas

  In the university we were given the following code sample and we were being told, that there is a memory leak when running this code. The sample should demonstrate that this is a situation where the garbage collector can't work. As far as my object oriented programming goes, the only codeline able to create a memory leak would be items=Arrays.copyOf(items,2 * size+1); The documentation says, that the elements are copied. Does that mean the reference is copied (and therefore another entry on the heap is created) or the object itself is being copied? As far as I know, Object and therefore Object[] are implemented as a reference type. So assigning a new value to 'items' would allow the garbage collector to find that the old 'item' is no longer referenced and can therefore be collected. In my eyes, this the codesample does not produce a memory leak. Could somebody prove me wrong? =) import java.util.Arrays; public class Foo { private Object[] items; private int size=0; private static final int ISIZE=10; public Foo() { items= new Object[ISIZE]; } public void push(final Object o){ checkSize(); items[size++]=o; } public Object pop(){ if (size==0) throw new ///... return items[--size]; } private void checkSize(){ if (items.length==size){ items=Arrays.copyOf(items,2 * size+1); } } }

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• Can JMX operations take interfaces as parameters?

  - by Thor84no

  I'm having problems with an MBean that takes a Map<String, Object> as a parameter. If I try to execute it via JMX using a proxy object, I get an Exception: Caused by: javax.management.ReflectionException at org.jboss.mx.server.AbstractMBeanInvoker.invoke(AbstractMBeanInvoker.java:231) at org.jboss.mx.server.MBeanServerImpl.invoke(MBeanServerImpl.java:668) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) Caused by: java.lang.IllegalArgumentException: Unable to find operation updateProperties(java.util.HashMap) It appears that it attempts to use the actual implementation class rather than the interface, and doesn't check if this is a child of the required interface. The same thing happens for extended classes (for example declare HashMap, pass in LinkedHashMap). Does this mean it's impossible to use an interface for such methods? At the moment I'm getting around it by changing the method signature to accept a HashMap, but it seems odd that I wouldn't be able to use interfaces (or extended classes) in my MBeans. Edit: The proxy object is being created by an in-house utility class called JmxInvocationHandler. The (hopefully) relevant parts of it are as follows: public class JmxInvocationHandler implements InvocationHandler { ... public static <T> T createMBean(final Class<T> iface, SFSTestProperties properties, String mbean, int shHostID) { T newProxyInstance = (T) Proxy.newProxyInstance(iface.getClassLoader(), new Class[] { iface }, (InvocationHandler) new JmxInvocationHandler(properties, mbean, shHostID)); return newProxyInstance; } ... private JmxInvocationHandler(SFSTestProperties properties, String mbean, int shHostID) { this.mbeanName = mbean + MBEAN_SUFFIX + shHostID; msConfig = new MsConfiguration(properties.getHost(0), properties.getMSAdminPort(), properties.getMSUser(), properties.getMSPassword()); } ... public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { if (management == null) { management = ManagementClientStore.getInstance().getManagementClient(msConfig.getHost(), msConfig.getAdminPort(), msConfig.getUser(), msConfig.getPassword(), false); } final Object result = management.methodCall(mbeanName, method.getName(), args == null? new Object[] {} : args); return result; } }

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• Need help extrapolating Java code

  - by Berlioz

  If anyone familiar with Rebecca Wirfs-Brock, she has a piece of Java code found in her book titled, Object Design: Roles, Responsibilities, and Collaborations. Here is the quote Applying Double Dispatch to a Specific Problem To implement the game Rock, Paper, Scissors we need to write code that determines whether one object “beats” another. The game has nine possible outcomes based on the three kinds of objects. The number of interactions is the cross product of the kinds of objects. Case or switch statements are often governed by the type of data that is being operated on. The object-oriented language equivalent is to base its actions on the class of some other object. In Java, it looks like this Here is the piece of Java code on page 16 ' import java.util.*; import java.lang.*; public class Rock { public static void main(String args[]) { } public static boolean beats(GameObject object) { if (object.getClass.getName().equals("Rock")) { result = false; } else if (object.getClass.getName().equals("Paper")) { result = false; } else if(object.getClass.getName().equals("Scissors")) { result = true; } return result; } }' ===This is not a very good solution. First, the receiver needs to know too much about the argument. Second, there is one of these nested conditional statements in each of the three classes. If new kinds of objects could be added to the game, each of the three classes would have to be modified. Can anyone share with me how to get this "less than optimal" piece of code to work in order to see it 'working'. She proceeds to demonstrate a better way, but I will spare you. Thanks

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• Concept: Information Into Memory Location.

  - by Richeve S. Bebedor

  I am having troubles conceptualizing an algorithm to be used to transform any information or data into a specific appropriate and reasonable memory location in any data structure that I will be devising. To give you an idea, I have a JPanel object instance and I created another Container type object instance of any subtype (note this is in Java because I love this language), then I collected those instances into a data structure not specifically just for those instances but also applicable to any type of object. Now my procedure for fetching those data again is to extract the object specific features similar in category to all object in that data structure and transform it into a integer data memory location (specifically as much as possible) or any type of data that will pertain to this transformation. And I can already access that memory location without further sorting or applications of O(n) time complex algorithms (which I think preferable but I wanted to do my own way XD). The data structure is of any type either binary tree, linked list, arrays or sets (and the like XD). What is important is I don't need to have successive comparing and analysis of data just to locate information in big structures. To give you a technical idea, I have to an array DS that contains JLabel object instance with a specific name "HelloWorld". But array DS contains other types of object (in multitude). Now this JLabel object has a location in the array at index [124324] (which is if you do any type of searching algorithm just to arrive at that location is conceivably slow because added to it the data structure used was an array *note please disregard the efficiency of the data structure to be used I just want to explain to you my concept XD). Now I want to equate "HelloWorld" to 124324 by using a conceptually made function applicable to all data types. So that I can do a direct search by doing this DS[extractLocation("HelloWorld")] just to get that JLabel instance. I know this may sound crazy but I want to test my concept of non-sorting feature extracting search algorithm for any data structure wherein my main problem is how to transform information to be stored into memory location of where it was stored.

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• Create and define Vector

  - by zdmytriv

  I'm looking for method to create Vector and push some values without defining variable Vector. For example: I have function: public function bla(data:Vector.<Object>):void { ... } this function expects Vector as parameter. I can pass parameters this way var newVector:Vector.<Object> = new Vector.<Object>(); newVector.push("bla1"); newVector.push("bla2"); bla(newVector); Can I do it in one line in Flex? I'm looking for something like: bla(new Vector.<Object>().push("bla1").push("bla2")); I've also tried this: bla(function():Vector.<Object> { var result:Vector.<Object> = new Vector.<Object>(2, true); result.push("bla1"); result.push("bla2"); return result; }); But it complains: 1067: Implicit coercion of a value of type Function to an unrelated type __AS3__.vec:Vector.<Object>... Thanks

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• Strange behavior when overloading methods in Java

  - by Sep

  I came across this weird (in my opinion) behavior today. Take this simple Test class: public class Test { public static void main(String[] args) { Test t = new Test(); t.run(); } private void run() { List<Object> list = new ArrayList<Object>(); list.add(new Object()); list.add(new Object()); method(list); } public void method(Object o) { System.out.println("Object"); } public void method(List<Object> o) { System.out.println("List of Objects"); } } It behaves the way you expect, printing "List of Objects". But if you change the following three lines: List<String> list = new ArrayList<String>(); list.add(""); list.add(""); you will get "Object" instead. I tried this a few other ways and got the same result. Is this a bug or is it a normal behavior? And if it is normal, can someone explain why? Thanks.

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