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  • C#/.NET Little Wonders &ndash; Cross Calling Constructors

    - by James Michael Hare
    Just a small post today, it’s the final iteration before our release and things are crazy here!  This is another little tidbit that I love using, and it should be fairly common knowledge, yet I’ve noticed many times that less experienced developers tend to have redundant constructor code when they overload their constructors. The Problem – repetitive code is less maintainable Let’s say you were designing a messaging system, and so you want to create a class to represent the properties for a Receiver, so perhaps you design a ReceiverProperties class to represent this collection of properties. Perhaps, you decide to make ReceiverProperties immutable, and so you have several constructors that you can use for alternative construction: 1: // Constructs a set of receiver properties. 2: public ReceiverProperties(ReceiverType receiverType, string source, bool isDurable, bool isBuffered) 3: { 4: ReceiverType = receiverType; 5: Source = source; 6: IsDurable = isDurable; 7: IsBuffered = isBuffered; 8: } 9: 10: // Constructs a set of receiver properties with buffering on by default. 11: public ReceiverProperties(ReceiverType receiverType, string source, bool isDurable) 12: { 13: ReceiverType = receiverType; 14: Source = source; 15: IsDurable = isDurable; 16: IsBuffered = true; 17: } 18:  19: // Constructs a set of receiver properties with buffering on and durability off. 20: public ReceiverProperties(ReceiverType receiverType, string source) 21: { 22: ReceiverType = receiverType; 23: Source = source; 24: IsDurable = false; 25: IsBuffered = true; 26: } Note: keep in mind this is just a simple example for illustration, and in same cases default parameters can also help clean this up, but they have issues of their own. While strictly speaking, there is nothing wrong with this code, logically, it suffers from maintainability flaws.  Consider what happens if you add a new property to the class?  You have to remember to guarantee that it is set appropriately in every constructor call. This can cause subtle bugs and becomes even uglier when the constructors do more complex logic, error handling, or there are numerous potential overloads (especially if you can’t easily see them all on one screen’s height). The Solution – cross-calling constructors I’d wager nearly everyone knows how to call your base class’s constructor, but you can also cross-call to one of the constructors in the same class by using the this keyword in the same way you use base to call a base constructor. 1: // Constructs a set of receiver properties. 2: public ReceiverProperties(ReceiverType receiverType, string source, bool isDurable, bool isBuffered) 3: { 4: ReceiverType = receiverType; 5: Source = source; 6: IsDurable = isDurable; 7: IsBuffered = isBuffered; 8: } 9: 10: // Constructs a set of receiver properties with buffering on by default. 11: public ReceiverProperties(ReceiverType receiverType, string source, bool isDurable) 12: : this(receiverType, source, isDurable, true) 13: { 14: } 15:  16: // Constructs a set of receiver properties with buffering on and durability off. 17: public ReceiverProperties(ReceiverType receiverType, string source) 18: : this(receiverType, source, false, true) 19: { 20: } Notice, there is much less code.  In addition, the code you have has no repetitive logic.  You can define the main constructor that takes all arguments, and the remaining constructors with defaults simply cross-call the main constructor, passing in the defaults. Yes, in some cases default parameters can ease some of this for you, but default parameters only work for compile-time constants (null, string and number literals).  For example, if you were creating a TradingDataAdapter that relied on an implementation of ITradingDao which is the data access object to retreive records from the database, you might want two constructors: one that takes an ITradingDao reference, and a default constructor which constructs a specific ITradingDao for ease of use: 1: public TradingDataAdapter(ITradingDao dao) 2: { 3: _tradingDao = dao; 4:  5: // other constructor logic 6: } 7:  8: public TradingDataAdapter() 9: { 10: _tradingDao = new SqlTradingDao(); 11:  12: // same constructor logic as above 13: }   As you can see, this isn’t something we can solve with a default parameter, but we could with cross-calling constructors: 1: public TradingDataAdapter(ITradingDao dao) 2: { 3: _tradingDao = dao; 4:  5: // other constructor logic 6: } 7:  8: public TradingDataAdapter() 9: : this(new SqlTradingDao()) 10: { 11: }   So in cases like this where you have constructors with non compiler-time constant defaults, default parameters can’t help you and cross-calling constructors is one of your best options. Summary When you have just one constructor doing the job of initializing the class, you can consolidate all your logic and error-handling in one place, thus ensuring that your behavior will be consistent across the constructor calls. This makes the code more maintainable and even easier to read.  There will be some cases where cross-calling constructors may be sub-optimal or not possible (if, for example, the overloaded constructors take completely different types and are not just “defaulting” behaviors). You can also use default parameters, of course, but default parameter behavior in a class hierarchy can be problematic (default values are not inherited and in fact can differ) so sometimes multiple constructors are actually preferable. Regardless of why you may need to have multiple constructors, consider cross-calling where you can to reduce redundant logic and clean up the code.   Technorati Tags: C#,.NET,Little Wonders

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  • JGoodies HashMap

    - by JohnMcClane
    Hi, I'm trying to build a chart program using presentation model. Using JGoodies for data binding was relatively easy for simple types like strings or numbers. But I can't figure out how to use it on a hashmap. I'll try to explain how the chart works and what my problem is: A chart consists of DataSeries, a DataSeries consists of DataPoints. I want to have a data model and to be able to use different views on the same model (e.g. bar chart, pie chart,...). Each of them consists of three classes. For example: DataPointModel: holds the data model (value, label, category) DataPointViewModel: extends JGoodies PresentationModel. wraps around DataPointModel and holds view properties like font and color. DataPoint: abstract class, extends JComponent. Different Views must subclass and implement their own ui. Binding and creating the data model was easy, but i don't know how to bind my data series model. package at.onscreen.chart; import java.beans.PropertyChangeListener; import java.beans.PropertyChangeSupport; import java.beans.PropertyVetoException; import java.util.Collection; import java.util.HashMap; import java.util.Iterator; public class DataSeriesModel { public static String PROPERTY_DATAPOINT = "dataPoint"; public static String PROPERTY_DATAPOINTS = "dataPoints"; public static String PROPERTY_LABEL = "label"; public static String PROPERTY_MAXVALUE = "maxValue"; /** * holds the data points */ private HashMap dataPoints; /** * the label for the data series */ private String label; /** * the maximum data point value */ private Double maxValue; /** * the model supports property change notification */ private PropertyChangeSupport propertyChangeSupport; /** * default constructor */ public DataSeriesModel() { this.maxValue = Double.valueOf(0); this.dataPoints = new HashMap(); this.propertyChangeSupport = new PropertyChangeSupport(this); } /** * constructor * @param label - the series label */ public DataSeriesModel(String label) { this.dataPoints = new HashMap(); this.maxValue = Double.valueOf(0); this.label = label; this.propertyChangeSupport = new PropertyChangeSupport(this); } /** * full constructor * @param label - the series label * @param dataPoints - an array of data points */ public DataSeriesModel(String label, DataPoint[] dataPoints) { this.dataPoints = new HashMap(); this.propertyChangeSupport = new PropertyChangeSupport(this); this.maxValue = Double.valueOf(0); this.label = label; for (int i = 0; i < dataPoints.length; i++) { this.addDataPoint(dataPoints[i]); } } /** * full constructor * @param label - the series label * @param dataPoints - a collection of data points */ public DataSeriesModel(String label, Collection dataPoints) { this.dataPoints = new HashMap(); this.propertyChangeSupport = new PropertyChangeSupport(this); this.maxValue = Double.valueOf(0); this.label = label; for (Iterator it = dataPoints.iterator(); it.hasNext();) { this.addDataPoint(it.next()); } } /** * adds a new data point to the series. if the series contains a data point with same id, it will be replaced by the new one. * @param dataPoint - the data point */ public void addDataPoint(DataPoint dataPoint) { String category = dataPoint.getCategory(); DataPoint oldDataPoint = this.getDataPoint(category); this.dataPoints.put(category, dataPoint); this.setMaxValue(Math.max(this.maxValue, dataPoint.getValue())); this.propertyChangeSupport.firePropertyChange(PROPERTY_DATAPOINT, oldDataPoint, dataPoint); } /** * returns the data point with given id or null if not found * @param uid - the id of the data point * @return the data point or null if there is no such point in the table */ public DataPoint getDataPoint(String category) { return this.dataPoints.get(category); } /** * removes the data point with given id from the series, if present * @param category - the data point to remove */ public void removeDataPoint(String category) { DataPoint dataPoint = this.getDataPoint(category); this.dataPoints.remove(category); if (dataPoint != null) { if (dataPoint.getValue() == this.getMaxValue()) { Double maxValue = Double.valueOf(0); for (Iterator it = this.iterator(); it.hasNext();) { DataPoint itDataPoint = it.next(); maxValue = Math.max(itDataPoint.getValue(), maxValue); } this.setMaxValue(maxValue); } } this.propertyChangeSupport.firePropertyChange(PROPERTY_DATAPOINT, dataPoint, null); } /** * removes all data points from the series * @throws PropertyVetoException */ public void removeAll() { this.setMaxValue(Double.valueOf(0)); this.dataPoints.clear(); this.propertyChangeSupport.firePropertyChange(PROPERTY_DATAPOINTS, this.getDataPoints(), null); } /** * returns the maximum of all data point values * @return the maximum of all data points */ public Double getMaxValue() { return this.maxValue; } /** * sets the max value * @param maxValue - the max value */ protected void setMaxValue(Double maxValue) { Double oldMaxValue = this.getMaxValue(); this.maxValue = maxValue; this.propertyChangeSupport.firePropertyChange(PROPERTY_MAXVALUE, oldMaxValue, maxValue); } /** * returns true if there is a data point with given category * @param category - the data point category * @return true if there is a data point with given category, otherwise false */ public boolean contains(String category) { return this.dataPoints.containsKey(category); } /** * returns the label for the series * @return the label for the series */ public String getLabel() { return this.label; } /** * returns an iterator over the data points * @return an iterator over the data points */ public Iterator iterator() { return this.dataPoints.values().iterator(); } /** * returns a collection of the data points. the collection supports removal, but does not support adding of data points. * @return a collection of data points */ public Collection getDataPoints() { return this.dataPoints.values(); } /** * returns the number of data points in the series * @return the number of data points */ public int getSize() { return this.dataPoints.size(); } /** * adds a PropertyChangeListener * @param listener - the listener */ public void addPropertyChangeListener(PropertyChangeListener listener) { this.propertyChangeSupport.addPropertyChangeListener(listener); } /** * removes a PropertyChangeListener * @param listener - the listener */ public void removePropertyChangeListener(PropertyChangeListener listener) { this.propertyChangeSupport.removePropertyChangeListener(listener); } } package at.onscreen.chart; import java.beans.PropertyVetoException; import java.util.Collection; import java.util.Iterator; import com.jgoodies.binding.PresentationModel; public class DataSeriesViewModel extends PresentationModel { /** * default constructor */ public DataSeriesViewModel() { super(new DataSeriesModel()); } /** * constructor * @param label - the series label */ public DataSeriesViewModel(String label) { super(new DataSeriesModel(label)); } /** * full constructor * @param label - the series label * @param dataPoints - an array of data points */ public DataSeriesViewModel(String label, DataPoint[] dataPoints) { super(new DataSeriesModel(label, dataPoints)); } /** * full constructor * @param label - the series label * @param dataPoints - a collection of data points */ public DataSeriesViewModel(String label, Collection dataPoints) { super(new DataSeriesModel(label, dataPoints)); } /** * full constructor * @param model - the data series model */ public DataSeriesViewModel(DataSeriesModel model) { super(model); } /** * adds a data point to the series * @param dataPoint - the data point */ public void addDataPoint(DataPoint dataPoint) { this.getBean().addDataPoint(dataPoint); } /** * returns true if there is a data point with given category * @param category - the data point category * @return true if there is a data point with given category, otherwise false */ public boolean contains(String category) { return this.getBean().contains(category); } /** * returns the data point with given id or null if not found * @param uid - the id of the data point * @return the data point or null if there is no such point in the table */ public DataPoint getDataPoint(String category) { return this.getBean().getDataPoint(category); } /** * returns a collection of the data points. the collection supports removal, but does not support adding of data points. * @return a collection of data points */ public Collection getDataPoints() { return this.getBean().getDataPoints(); } /** * returns the label for the series * @return the label for the series */ public String getLabel() { return this.getBean().getLabel(); } /** * sets the max value * @param maxValue - the max value */ public Double getMaxValue() { return this.getBean().getMaxValue(); } /** * returns the number of data points in the series * @return the number of data points */ public int getSize() { return this.getBean().getSize(); } /** * returns an iterator over the data points * @return an iterator over the data points */ public Iterator iterator() { return this.getBean().iterator(); } /** * removes all data points from the series * @throws PropertyVetoException */ public void removeAll() { this.getBean().removeAll(); } /** * removes the data point with given id from the series, if present * @param category - the data point to remove */ public void removeDataPoint(String category) { this.getBean().removeDataPoint(category); } } package at.onscreen.chart; import java.beans.PropertyChangeEvent; import java.beans.PropertyChangeListener; import java.beans.PropertyVetoException; import java.util.Collection; import java.util.Iterator; import javax.swing.JComponent; public abstract class DataSeries extends JComponent implements PropertyChangeListener { /** * the model */ private DataSeriesViewModel model; /** * default constructor */ public DataSeries() { this.model = new DataSeriesViewModel(); this.model.addPropertyChangeListener(this); this.createComponents(); } /** * constructor * @param label - the series label */ public DataSeries(String label) { this.model = new DataSeriesViewModel(label); this.model.addPropertyChangeListener(this); this.createComponents(); } /** * full constructor * @param label - the series label * @param dataPoints - an array of data points */ public DataSeries(String label, DataPoint[] dataPoints) { this.model = new DataSeriesViewModel(label, dataPoints); this.model.addPropertyChangeListener(this); this.createComponents(); } /** * full constructor * @param label - the series label * @param dataPoints - a collection of data points */ public DataSeries(String label, Collection dataPoints) { this.model = new DataSeriesViewModel(label, dataPoints); this.model.addPropertyChangeListener(this); this.createComponents(); } /** * full constructor * @param model - the model */ public DataSeries(DataSeriesViewModel model) { this.model = model; this.model.addPropertyChangeListener(this); this.createComponents(); } /** * creates, binds and configures UI components. * data point properties can be created here as components or be painted in paintComponent. */ protected abstract void createComponents(); @Override public void propertyChange(PropertyChangeEvent evt) { this.repaint(); } /** * adds a data point to the series * @param dataPoint - the data point */ public void addDataPoint(DataPoint dataPoint) { this.model.addDataPoint(dataPoint); } /** * returns true if there is a data point with given category * @param category - the data point category * @return true if there is a data point with given category, otherwise false */ public boolean contains(String category) { return this.model.contains(category); } /** * returns the data point with given id or null if not found * @param uid - the id of the data point * @return the data point or null if there is no such point in the table */ public DataPoint getDataPoint(String category) { return this.model.getDataPoint(category); } /** * returns a collection of the data points. the collection supports removal, but does not support adding of data points. * @return a collection of data points */ public Collection getDataPoints() { return this.model.getDataPoints(); } /** * returns the label for the series * @return the label for the series */ public String getLabel() { return this.model.getLabel(); } /** * sets the max value * @param maxValue - the max value */ public Double getMaxValue() { return this.model.getMaxValue(); } /** * returns the number of data points in the series * @return the number of data points */ public int getDataPointCount() { return this.model.getSize(); } /** * returns an iterator over the data points * @return an iterator over the data points */ public Iterator iterator() { return this.model.iterator(); } /** * removes all data points from the series * @throws PropertyVetoException */ public void removeAll() { this.model.removeAll(); } /** * removes the data point with given id from the series, if present * @param category - the data point to remove */ public void removeDataPoint(String category) { this.model.removeDataPoint(category); } /** * returns the data series view model * @return - the data series view model */ public DataSeriesViewModel getViewModel() { return this.model; } /** * returns the data series model * @return - the data series model */ public DataSeriesModel getModel() { return this.model.getBean(); } } package at.onscreen.chart.builder; import java.util.Collection; import net.miginfocom.swing.MigLayout; import at.onscreen.chart.DataPoint; import at.onscreen.chart.DataSeries; import at.onscreen.chart.DataSeriesViewModel; public class BuilderDataSeries extends DataSeries { /** * default constructor */ public BuilderDataSeries() { super(); } /** * constructor * @param label - the series label */ public BuilderDataSeries(String label) { super(label); } /** * full constructor * @param label - the series label * @param dataPoints - an array of data points */ public BuilderDataSeries(String label, DataPoint[] dataPoints) { super(label, dataPoints); } /** * full constructor * @param label - the series label * @param dataPoints - a collection of data points */ public BuilderDataSeries(String label, Collection dataPoints) { super(label, dataPoints); } /** * full constructor * @param model - the model */ public BuilderDataSeries(DataSeriesViewModel model) { super(model); } @Override protected void createComponents() { this.setLayout(new MigLayout()); /* * * I want to add a new BuilderDataPoint for each data point in the model. * I want the BuilderDataPoints to be synchronized with the model. * e.g. when a data point is removed from the model, the BuilderDataPoint shall be removed * from the BuilderDataSeries * */ } } package at.onscreen.chart.builder; import javax.swing.JFormattedTextField; import javax.swing.JTextField; import at.onscreen.chart.DataPoint; import at.onscreen.chart.DataPointModel; import at.onscreen.chart.DataPointViewModel; import at.onscreen.chart.ValueFormat; import com.jgoodies.binding.adapter.BasicComponentFactory; import com.jgoodies.binding.beans.BeanAdapter; public class BuilderDataPoint extends DataPoint { /** * default constructor */ public BuilderDataPoint() { super(); } /** * constructor * @param category - the category */ public BuilderDataPoint(String category) { super(category); } /** * constructor * @param value - the value * @param label - the label * @param category - the category */ public BuilderDataPoint(Double value, String label, String category) { super(value, label, category); } /** * full constructor * @param model - the model */ public BuilderDataPoint(DataPointViewModel model) { super(model); } @Override protected void createComponents() { BeanAdapter beanAdapter = new BeanAdapter(this.getModel(), true); ValueFormat format = new ValueFormat(); JFormattedTextField value = BasicComponentFactory.createFormattedTextField(beanAdapter.getValueModel(DataPointModel.PROPERTY_VALUE), format); this.add(value, "w 80, growx, wrap"); JTextField label = BasicComponentFactory.createTextField(beanAdapter.getValueModel(DataPointModel.PROPERTY_LABEL)); this.add(label, "growx, wrap"); JTextField category = BasicComponentFactory.createTextField(beanAdapter.getValueModel(DataPointModel.PROPERTY_CATEGORY)); this.add(category, "growx, wrap"); } } To sum it up: I need to know how to bind a hash map property to JComponent.components property. JGoodies is in my opinion not very well documented, I spent a long time searching through the internet, but I did not find any solution to my problem. Hope you can help me.

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  • Scala: is it possible to override default case class constructor?

    - by adam77
    Just wondering if this is possible. What I would actually like to do is check and possibly modify one of the arguments before it is stored as a val. Alternatively, I could use an overload and make the default constructor private. In which case I would also like to make private the default factory constructor in the companion object, how would I do that? Many thanks. Adam

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  • Why does JPA require a no-arg constructor for domain objects ?

    - by Jacques René Mesrine
    Why does JPA require a no-arg constructor for domain objects ? I am using eclipselink and just got this exception during deployment. Exception [EclipseLink-63] (Eclipse Persistence Services-1.1.0.r3639-SNAPSHOT): org.eclipse.persistence.exceptions.DescriptorException Exception Description: The instance creation method [com.me.model.UserVO.<Default Constructor>], with no parameters, does not exist, or is not accessible. Internal Exception: java.lang.NoSuchMethodException: com.me.model.UserVO.<init>() Descriptor: RelationalDescriptor(com.me.model.UserVO --> [DatabaseTable(user)])

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  • In this example where is the C++ assignment operator used rather than the copy constructor ?

    - by Bill Forster
    As part of an ongoing process of trying to upgrade my C++ skills, I am trying to break some old habits. My old school C programmer inclination is to write this; void func( Widget &ref ) { Widget w; // default constructor int i; for( i=0; i<10; i++ ) { w = ref; // assignment operator // do stuff that modifies w } } This works well. But I think the following is closer to best practice; void func( Widget &ref ) { for( int i=0; i<10; i++ ) { Widget w = ref; // ?? // do stuff that modifies w } } With my Widget class at least, this works fine. But I don't fully understand why. I have two theories; 1) The copy constructor runs 10 times. 2) The copy constructor runs once then the assignment operator runs 9 times. Both of these trouble me a little. 2) in particular seems artificial and wrong. Is there a third possibility that I am missing ?

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  • Why default constructor does not appear for value types?

    - by Arun
    The below snippet gives me a list of constructors and methods of a type. static void ReflectOnType(Type type) { Console.WriteLine(type.FullName); Console.WriteLine("------------"); List<ConstructorInfo> constructors = type.GetConstructors(BindingFlags.Public | BindingFlags.Static | BindingFlags.NonPublic |BindingFlags.Instance | BindingFlags.Default).ToList(); List<MethodInfo> methods = type.GetMethods().ToList(); Type baseType = type.BaseType; while (baseType != null) { constructors.AddRange(baseType.GetConstructors(BindingFlags.Public | BindingFlags.Static | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Default)); methods.AddRange(baseType.GetMethods()); baseType = baseType.BaseType; } Console.WriteLine("Reflection on {0} type", type.Name); for (int i = 0; i < constructors.Count; i++) { Console.Write("Constructor: {0}.{1}", constructors[i].DeclaringType.Name, constructors[i].Name); Console.Write("("); ParameterInfo[] parameterInfos = constructors[i].GetParameters(); if (parameterInfos.Length > 0) { for (int j = 0; j < parameterInfos.Length; j++) { if (j > 0) { Console.Write(", "); } Console.Write("{0} {1}", parameterInfos[j].ParameterType, parameterInfos[j].Name); } } Console.Write(")"); if (constructors[i].IsSpecialName) { Console.Write(" has 'SpecialName' attribute"); } Console.WriteLine(); } Console.WriteLine(); for (int i = 0; i < methods.Count; i++) { Console.Write("Method: {0}.{1}", methods[i].DeclaringType.Name, methods[i].Name); // Determine whether or not each field is a special name. if (methods[i].IsSpecialName) { Console.Write(" has 'SpecialName' attribute"); } Console.WriteLine(); } } But when I pass an ‘int’ type to this method, why don’t I see the implicit constructor in the output? Or, how do I modify the above code to list the default constructor as well (in case I’m missing something in my code).

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  • Invoke an Overloaded Constructor through this keyword (What's the Different between this two Sample code?)

    - by Alireza Dehqani
    using System; namespace ConsoleApplication1 { class Program { static void Main() { // Sample Sample ob = new Sample(); // line1 // Output for line1 /* * Sample(int i) * Sample() / // Sample2 Sample2 ob2 = new Sample2(); // line2 // Output for line2 / * Sample2() */ } } class Sample { // Fields private int a; // Constructors public Sample(int i) // Main Constructor { Console.WriteLine(" Sample(int i)"); a = i; } // Default Constructor public Sample() : this(0) { Console.WriteLine(" Sample()"); } } class Sample2 { // fields private int a; // Constructors public Sample2(int i) { Console.WriteLine("Sample2(int i)"); a = i; } public Sample2() { Console.WriteLine("Sample2()"); a = 0; } } }

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  • How to access controller dynamic properties within a base controller's constructor in Grails?

    - by 4h34d
    Basically, I want to be able to assign objects created within filters to members in a base controller from which every controller extends. Any possible way to do that? Here's how I tried, but haven't got to make it work. What I'm trying to achieve is to have all my controllers extend a base controller. The base controller's constructor would be used to assign values to its members, those values being pulled from the session map. Example below. File grails-app/controllers/HomeController.groovy: class HomeController extends BaseController { def index = { render username } } File grails-app/controllers/BaseController.groovy: abstract class BaseController { public String username public BaseController() { username = session.username } } When running the app, the output shown is: 2010-06-15 18:17:16,671 [main] ERROR [localhost].[/webapp] - Exception sending context initialized event to listener instance of class org.codehaus.groovy.grails.web.context.GrailsContextLoaderListener org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'pluginManager' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Invocation of init method failed; nested exception is java.lang.RuntimeException: Unable to locate constructor with Class parameter for class org.codehaus.groovy.grails.commons.DefaultGrailsControllerClass ... Caused by: java.lang.RuntimeException: Unable to locate constructor with Class parameter for class org.codehaus.groovy.grails.commons.DefaultGrailsControllerClass ... Caused by: java.lang.reflect.InvocationTargetException ... Caused by: org.codehaus.groovy.grails.exceptions.NewInstanceCreationException: Could not create a new instance of class [com.my.package.controller.HomeController]! ... Caused by: groovy.lang.MissingPropertyException: No such property: session for class: com.my.package.controller.HomeController at com.my.package.controller.BaseController.<init>(BaseController.groovy:16) at com.my.package.controller.HomeController.<init>(HomeController.groovy) ... 2010-06-15 18:17:16,687 [main] ERROR core.StandardContext - Error listenerStart 2010-06-15 18:17:16,687 [main] ERROR core.StandardContext - Context [/webapp] startup failed due to previous errors And the app won't run. This is just an example as in my case I wouldn't want to assign a username to a string value, but rather a few objects pulled from the session map. The objects pulled from the session map are being set within filters. The alternative I see is being able to access the controller's instance within the filter's execution. Is that possible? Please help! Thanks a bunch!

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  • Is wrapping new within the constructor good or bad?

    - by Timothy
    I watched John Resig's Best Practices in JavaScript Library Design presentation; one slide suggested "tweaking" the object constructor so it instantiates itself. function jQuery(str, con) { if (window === this) { return new jQuery(str, con); } // ... } With that, new jQuery("#foo") becomes jQuery("# foo"). I thought it was rather interesting, but I haven't written a constructor like that in my own code. A little later I read a post here on SO. (Sorry, I don't remember which or I'd supply a link. I will update the question if I can find it again.) One of the comments said it was bad practice to hide new from the programmer like that, but didn't go into details. My question is, it the above generally considered good, bad, or indifferent, and why?

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  • Solving a cyclical dependency in Ninject (Compact Framework)

    - by Alex
    I'm trying to use Ninject for dependency injection in my MVP application. However, I have a problem because I have two types that depend on each other, thus creating a cyclic dependency. At first, I understand that it was a problem, because I had both types require each other in their constructors. Therefore, I moved one of the dependencies to a property injection instead, but I'm still getting the error message. What am I doing wrong? This is the presenter: public class LoginPresenter : Presenter<ILoginView>, ILoginPresenter { public LoginPresenter( ILoginView view ) : base( view ) { } } and this is the view: public partial class LoginForm : Form, ILoginView { [Inject] public ILoginPresenter Presenter { private get; set; } public LoginForm() { InitializeComponent(); } } And here's the code that causes the exception: static class Program { /// <summary> /// The main entry point for the application. /// </summary> [MTAThread] static void Main() { // Show the login form Views.LoginForm loginForm = Kernel.Get<Views.Interfaces.ILoginView>() as Views.LoginForm; Application.Run( loginForm ); } } The exception happens on the line with the Kernel.Get<>() call. Here it is: Error activating ILoginPresenter using binding from ILoginPresenter to LoginPresenter A cyclical dependency was detected between the constructors of two services. Activation path: 4) Injection of dependency ILoginPresenter into property Presenter of type LoginForm 3) Injection of dependency ILoginView into parameter view of constructor of type LoginPresenter 2) Injection of dependency ILoginPresenter into property Presenter of type LoginForm 1) Request for ILoginView Suggestions: 1) Ensure that you have not declared a dependency for ILoginPresenter on any implementations of the service. 2) Consider combining the services into a single one to remove the cycle. 3) Use property injection instead of constructor injection, and implement IInitializable if you need initialization logic to be run after property values have been injected. Why doesn't Ninject understand that since one is constructor injection and the other is property injection, this can work just fine? I even read somewhere looking for the solution to this problem that Ninject supposedly gets this right as long as the cyclic dependency isn't both in the constructors. Apparently not, though. Any help resolving this would be much appreciated.

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  • Use of private constructor to prevent instantiation of class?

    - by cringe
    Hi guys! Right now I'm thinking about adding a private constructor to a class that only holds some String constants. public class MyStrings { // I want to add this: private MyString() {} public static final String ONE = "something"; public static final String TWO = "another"; ... } Is there any performance or memory overhead if I add a private constructor to this class to prevent someone to instantiate it? Do you think it's necessary at all or that private constructors for this purpose are a waste of time and code clutter?

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  • Codeigniter - Is it ok to add functionality to the constructor in controllers?

    - by Irro
    I'm making a project where I want the user to search for shops in different cities and would like the url to be like this: domain/shop/city/name. So I created a controller in codeigniter called Shop. But I cant create a city function since the city part of the url changes dependent on city name. One easy way to do it would be to add a function called "search" and add the functionality there but then I get url's like: domain/shop/search/city/name which I really would like to avoid. So my question is if it's ok to add my functionality directly into the constructor to avoid that extra "search" part in the url? I'm afraid that there might be some performance tricks involved that potentially keeps the class in memory so the constructor will not be called every time.

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  • How does C++ free the memory when a constructor throws an exception and a custom new is used

    - by Joshua
    I see the following constructs: new X will free the memory if X constructor throws. operator new() can be overloaded. The canonical definition of an operator new overload is void *operator new(heap h) and the corrisponding operator delete. The most common operator new overload is pacement new, which is void *operator new(void *p) { return p; } You almost always cannot call delete on the pointer given to placement new. This leads to a single question. How is memory cleaned up when X constructor throws and an overloaded new is used?

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  • Why I am forced to write the (Data Constructor) name with first letter in small case?

    - by Optimight
    Why I am forced to write "liOfLi" in place of "LiOfLi"? Please guide. code in baby.hs LiOfLi = [ [1,3,4,5,6,8], [ 12, 13, 15, 16, 19, 20], [23, 24, 25, 45, 56] ] ghci response: ghci :l baby [1 of 1] Compiling Main ( baby.hs, interpreted ) Failed, modules loaded: none. ghci baby.hs:29:1: Not in scope: data constructor `LiOfLi' When changing the initial letter to smaller case code in baby.hs liOfLi = [ [1,3,4,5,6,8], [ 12, 13, 15, 16, 19, 20], [23, 24, 25, 45, 56] ] ghci response: ghci :l baby [1 of 1] Compiling Main ( baby.hs, interpreted ) Ok, modules loaded: Main. Following are the SO questions I refered but I failed to understand the rules/ logic and get the answer for (my) abovementioned question. Why does Haskell force data constructor's first letter to be upper case? the variable names need to be lowercase. The official documentation related to this is at haskell.org/onlinereport/intro.html#namespaces – (the SO comment by) Chris Kuklewicz

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  • JavaScript Class Patterns &ndash; In CoffeeScript

    - by Liam McLennan
    Recently I wrote about JavaScript class patterns, and in particular, my favourite class pattern that uses closure to provide encapsulation. A class to represent a person, with a name and an age, looks like this: var Person = (function() { // private variables go here var name,age; function constructor(n, a) { name = n; age = a; } constructor.prototype = { toString: function() { return name + " is " + age + " years old."; } }; return constructor; })(); var john = new Person("John Galt", 50); console.log(john.toString()); Today I have been experimenting with coding for node.js in CoffeeScript. One of the first things I wanted to do was to try and implement my class pattern in CoffeeScript and then see how it compared to CoffeeScript’s built-in class keyword. The above Person class, implemented in CoffeeScript, looks like this: # JavaScript style class using closure to provide private methods Person = (() -> [name,age] = [{},{}] constructor = (n, a) -> [name,age] = [n,a] null constructor.prototype = toString: () -> "name is #{name} age is #{age} years old" constructor )() I am satisfied with how this came out, but there are a few nasty bits. To declare the two private variables in javascript is as simple as var name,age; but in CoffeeScript I have to assign a value, hence [name,age] = [{},{}]. The other major issue occurred because of CoffeeScript’s implicit function returns. The last statement in any function is returned, so I had to add null to the end of the constructor to get it to work. The great thing about the technique just presented is that it provides encapsulation ie the name and age variables are not visible outside of the Person class. CoffeeScript classes do not provide encapsulation, but they do provide nicer syntax. The Person class using native CoffeeScript classes is: # CoffeeScript style class using the class keyword class CoffeePerson constructor: (@name, @age) -> toString: () -> "name is #{@name} age is #{@age} years old" felix = new CoffeePerson "Felix Hoenikker", 63 console.log felix.toString() So now I have a trade-off: nice syntax against encapsulation. I think I will experiment with both strategies in my project and see which works out better.

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  • Oracle Solaris 11 ?????????:?Oracle Solaris 11 ?????·????·??? ?2????

    - by kazun
    2012?2?20???????????? ??13F????????????Oracle Solaris 11???????????Oracle Solaris 11 ?????·????·????????????????????????2??????????Automated Installer(AI)???Distribution Constructor??????????????????????????????50????????????????????????????????? Oracle Solaris 11 ????????? - ?????????????????? - ???????????????????????? - 2????????????????? ???? Oracle 11 ??????? ?Oracle Solaris 11 ??????????????·??????????(???????? ??????????? ????????????? ??? ??? ??:???)???Oracle Solaris 11????????????????????????? Oracle Solaris 11 ???Oracle Solaris 10 ??????????????????????????2?????????????????(????????GUI???)???????????????????????????????????????????????????????????????????????????????????????????????????????????? ?????????? ???????????????:Automated Installer ????????"hands-free"??????????? Automated Installer?(?? ???????????? ??????????? ?????????????? ??????????????:???)???Oracle Solaris 11 ???????Automated Installer (AI)????????? AI????????????????????Solaris Zones ???????????????????????????????????????????????????????????????????????????????????????Jumpstart ?????????????????? AI?Image Packaging System (IPS)????????????????????????????????????OS???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????AI??????(XML?????????????)?SC???????????????????????????????????????????????????????????????????????? ??????????????????????????????????AI ???????????DHCP ????????????????????????????? VirtualBox ??????????????? ?:Oracle Solaris Studio ??? AI??????????????????????? ?????????? ???????????????????:Distribution Constructor ?????????????????????????????????????????????? Distribution Constructor?(?? ???????????? ??????????? ????????????? ??????????????:???)???? ?????????Oracle Solaris 11 ????????????????????????????????????? "Distribution Constructor" ?????????????"Distribution Constructor" ???????????????????????????????????????????????????????????????????????????"Distribution Constructor"???LiveCD/USB???????????????ISO?????3???OS?????????????????????Distribution Constructor?????????????????????????????????????????????????????????????????????Distribution Constructor??Solaris ?ZFS???????????AI??????????????????????????XML??????????? ?????????3??????????????????????????????????????????????????????IPS??????????????custom-script????????????????????????????????????????????????????????????????????????? ???????????????????????????????? ?????????? Oracle Solaris ??????? ??????????Installer Disk(3??DVD)????????????????????????Oracle Solaris Live CD(x86)??1???Oracle Solaris 11 Interactive Text Installer??SPARC??x86?????1???????????Live CD??????????Solaris 11 ?????????????????????Interactive Text Installer ??????????????(???????????????????????????????)?Interactive Text Installer ???????????????????????????????????? ???Solaris 11 VM???? for Oracle VM VirtualBox ?????????????????????(?Solaris 11 VM ???? for Oracle VM VirtualBox ???????Oracle VM for x86 ????????)? Oracle VM VirtualBox??????? Solaris 11 VM???? for Oracle VM VirtualBox??????? Oracle Solaris 11?????????????????????????? ?????? Oracle Solaris 10 JumpStart ?? Oracle Solaris 11 ???????????? ???? Oracle Solaris 11 ????????????? Oracle Solaris 11 ???????????

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  • Spring: Using "Lookup method injection" for my ThreadFactory looks not scalable.

    - by Michael Bavin
    Hi, We're building a ThreadFactory so everytime a singleton controller needs a new thread, i get a new instance everytime. Looking at Lookup method injection looks good but what if we have multiple threads. like: public abstract class ThreadManager { public abstract Thread createThreadDoA(); public abstract Thread createThreadDoB(); } and config: <bean id="threadManager" class="bla.ThreadManager" singleton="true"> <lookup-method name="createThreadA" bean="threadA" /> <lookup-method name="createThreadB" bean="threadB"/> </bean> <bean id="threadA" class="bla.ThreadA"> <bean id="threadB" class="bla.ThreadB"> and usage: threadManager.createThreadA(); I don't want to create an abstract "create" method for every new threadclass. Is it possible to make this generich like: threadManager.createThread(ThreadA.class); Thank you

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  • C# and MySQL .NET Connector - Any way of preventing SQL Injection attacks in a generic class?

    - by John M
    My idea is to create some generic classes for Insert/Update/Select via a C# (3.5) Winforms app talking with a MySQL database via MySQL .NET Connector 6.2.2. For example: public void Insert(string strSQL) { if (this.OpenConnection() == true) { MySqlCommand cmd = new MySqlCommand(strSQL, connection); cmd.ExecuteNonQuery(); this.CloseConnection(); } } Then from anywhere in the program I can run a query with/without user input by just passing a SQL query string. Reading around on SO is starting to give me the indication that this may lead to SQL injection attacks (for any user-input values). Is there anyway of scrubbing the inputted strSQL or do I need to go and create individual parameterized queries in every method that needs to do a database function?

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