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  • How to initialize List<E> in empty class constructor?

    - by Nazgulled
    Hi, The following code obviously doesn't work because List<E> is abstract: public class MyList { private List<E> list; public MyList() { this.list = new List<E>(); } } How can I initialize MyList class with an empty constructor if I need the list variable to be a LinkedList or a ArrayList depending on my needs?

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  • a constructor as a delegate - is it possible in C#?

    - by akavel
    I have a class like below: class Foo { public Foo(int x) { ... } } and I need to pass to a certain method a delegate like this: delegate Foo FooGenerator(int x); Is it possible to pass the constructor directly as a FooGenerator value, without having to type: delegate(int x) { return new Foo(x); } ? EDIT: For my personal use, the question refers to .NET 2.0, but hints/responses for 3.0+ are welcome as well.

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  • Can't I send NULL as a parameter with a constructor?

    - by Jason94
    Lets say i have a Shape object that has a constructor like this: Shape( width, height, radius, depth ) Now, I just have a silly rect so i dont need redius and depth... is it okey to do Shape myRect(50, 50, NULL, NULL) ? I know its not the best idea and I should use inheritance and stuff but this is the mess im in so can i use NULL like this?

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  • How to add a constructor to a subclassed numeric type?

    - by abbot
    I want to subclass a numeric type (say, int) in python and give it a shiny complex constructor. Something like this: class NamedInteger(int): def __init__(self, value): super(NamedInteger, self).__init__(value) self.name = 'pony' def __str__(self): return self.name x = NamedInteger(5) print x + 3 print str(x) This works fine under Python 2.4, but Python 2.6 gives a deprecation warning. What is the best way to subclass a numeric type and to redefine constructors for builtin types in newer Python versions?

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  • C++, is it possible to call a constructor directly, without new?

    - by osgx
    Hello Can I call constructor explicitly, without using new, if I already have a memory for object? // class Object1{char *str;public:Object1(char*str):str(str){puts("ctor");puts(str);};~Object1(){puts("dtor");puts(str);}}; Object1 ooo[2] = {Object1("I'm the first object"), Object1("I'm the 2nd")}; do_smth_useful(ooo); ooo[0].~Object1(); // call destructor ooo[0].Object1("I'm the 3rd object in place of first"); // ???? - reuse memory

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  • How is the default constructor of System.Drawing.Graphics removed?

    - by Albert Iordache
    When I try to create an object of Graphics, why doesn't the following work? System.Drawing.Graphics graphicsObj = new System.Drawing.Graphics(); (I am aware that I could create a private System.Windows.Forms.Panel Obj; and then do CreateGraphics() if I wanted it to work) I tried to find a custom constructor for Graphics, but I couldn't find one. Where did Microsoft define it, or how did it block it?

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  • What does a static modifier on a constructor means?

    - by the_drow
    I saw this kind of code at work: class FooPlugin : IPlugin // IPlugin is a Microsoft CRM component, it has something special about it's execution { static FooPlugin() { SomeObject.StaticFunction(); // The guy who wrote it said it's meaningful to this question but he can't remember why. } } Any idea what does a static modifier on a constructor mean and why in this case it is required?

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  • JavaScript inheritance extend function

    - by Zach
    I'm having some trouble understanding the IF clause at the end of this function from Pro JavaScript Design Patterns: function extend(subClass, superClass) { var F = function() {}; F.prototype = superClass.prototype; subClass.prototype = new F(); subClass.prototype.constructor = subClass; subClass.superclass = superClass.prototype; if(superClass.prototype.constructor == Object.prototype.constructor) { superClass.prototype.constructor = superClass; } } The book explains that these lines ensure that the superclass's constructor attribute is correctly set, even if the superclass is the Object class itself. Yet, if I omit those three lines and do the following: function SubClass() {}; extend(SubClass, Object); alert(Object.prototype.constructor == Object); The alert says 'true', which means the superclass's constructor is set correctly even without those last three lines. Under what conditions, then, does this IF statement do something useful? Thanks.

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  • readonly keyword

    - by nmarun
    This is something new that I learned about the readonly keyword. Have a look at the following class: 1: public class MyClass 2: { 3: public string Name { get; set; } 4: public int Age { get; set; } 5:  6: private readonly double Delta; 7:  8: public MyClass() 9: { 10: Initializer(); 11: } 12:  13: public MyClass(string name = "", int age = 0) 14: { 15: Name = name; 16: Age = age; 17: Initializer(); 18: } 19:  20: private void Initializer() 21: { 22: Delta = 0.2; 23: } 24: } I have a couple of public properties and a private readonly member. There are two constructors – one that doesn’t take any parameters and the other takes two parameters to initialize the public properties. I’m also calling the Initializer method in both constructors to initialize the readonly member. Now when I build this, the code breaks and the Error window says: “A readonly field cannot be assigned to (except in a constructor or a variable initializer)” Two things after I read this message: It’s such a negative statement. I’d prefer something like: “A readonly field can be assigned to (or initialized) only in a constructor or through a variable initializer” But in my defense, I AM assigning it in a constructor (only indirectly). All I’m doing is creating a method that does it and calling it in a constructor. Turns out, .net was not ‘frameworked’ this way. We need to have the member initialized directly in the constructor. If you have multiple constructors, you can just use the ‘this’ keyword on all except the default constructors to call the default constructor. This default constructor can then initialize your readonly members. This will ensure you’re not repeating the code in multiple places. A snippet of what I’m talking can be seen below: 1: public class Person 2: { 3: public int UniqueNumber { get; set; } 4: public string Name { get; set; } 5: public int Age { get; set; } 6: public DateTime DateOfBirth { get; set; } 7: public string InvoiceNumber { get; set; } 8:  9: private readonly string Alpha; 10: private readonly int Beta; 11: private readonly double Delta; 12: private readonly double Gamma; 13:  14: public Person() 15: { 16: Alpha = "FDSA"; 17: Beta = 2; 18: Delta = 3.0; 19: Gamma = 0.0989; 20: } 21:  22: public Person(int uniqueNumber) : this() 23: { 24: UniqueNumber = uniqueNumber; 25: } 26: } See the syntax in line 22 and you’ll know what I’m talking about. So the default constructor gets called before the one in line 22. These are known as constructor initializers and they allow one constructor to call another. The other ‘myth’ I had about readonly members is that you can set it’s value only once. This was busted as well (I recall Adam and Jamie’s show). Say you’ve initialized the readonly member through a variable initializer. You can over-write this value in any of the constructors any number of times. 1: public class Person 2: { 3: public int UniqueNumber { get; set; } 4: public string Name { get; set; } 5: public int Age { get; set; } 6: public DateTime DateOfBirth { get; set; } 7: public string InvoiceNumber { get; set; } 8:  9: private readonly string Alpha = "asdf"; 10: private readonly int Beta = 15; 11: private readonly double Delta = 0.077; 12: private readonly double Gamma = 1.0; 13:  14: public Person() 15: { 16: Alpha = "FDSA"; 17: Beta = 2; 18: Delta = 3.0; 19: Gamma = 0.0989; 20: } 21:  22: public Person(int uniqueNumber) : this() 23: { 24: UniqueNumber = uniqueNumber; 25: Beta = 3; 26: } 27:  28: public Person(string name, DateTime dob) : this() 29: { 30: Name = name; 31: DateOfBirth = dob; 32:  33: Alpha = ";LKJ"; 34: Gamma = 0.0898; 35: } 36:  37: public Person(int uniqueNumber, string name, int age, DateTime dob, string invoiceNumber) : this() 38: { 39: UniqueNumber = uniqueNumber; 40: Name = name; 41: Age = age; 42: DateOfBirth = dob; 43: InvoiceNumber = invoiceNumber; 44:  45: Alpha = "QWER"; 46: Beta = 5; 47: Delta = 1.0; 48: Gamma = 0.0; 49: } 50: } In the above example, every constructor over-writes the values for the readonly members. This is perfectly valid. There is a possibility that based on the way the object is instantiated, the readonly member will have a different value. Well, that’s all I have for today and read this as it’s on a related topic.

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  • How to create a simple adf dashboard application with EJB 3.0

    - by Rodrigues, Raphael
    In this month's Oracle Magazine, Frank Nimphius wrote a very good article about an Oracle ADF Faces dashboard application to support persistent user personalization. You can read this entire article clicking here. The idea in this article is to extend the dashboard application. My idea here is to create a similar dashboard application, but instead ADF BC model layer, I'm intending to use EJB3.0. There are just a one small trick here and I'll show you. I'm using the HR usual oracle schema. The steps are: 1. Create a ADF Fusion Application with EJB as a layer model 2. Generate the entities from table (I'm using Department and Employees only) 3. Create a new Session Bean. I called it: HRSessionEJB 4. Create a new method like that: public List getAllDepartmentsHavingEmployees(){ JpaEntityManager jpaEntityManager = (JpaEntityManager)em.getDelegate(); Query query = jpaEntityManager.createNamedQuery("Departments.allDepartmentsHavingEmployees"); JavaBeanResult.setQueryResultClass(query, AggregatedDepartment.class); return query.getResultList(); } 5. In the Departments entity, create a new native query annotation: @Entity @NamedQueries( { @NamedQuery(name = "Departments.findAll", query = "select o from Departments o") }) @NamedNativeQueries({ @NamedNativeQuery(name="Departments.allDepartmentsHavingEmployees", query = "select e.department_id, d.department_name , sum(e.salary), avg(e.salary) , max(e.salary), min(e.salary) from departments d , employees e where d.department_id = e.department_id group by e.department_id, d.department_name")}) public class Departments implements Serializable {...} 6. Create a new POJO called AggregatedDepartment: package oramag.sample.dashboard.model; import java.io.Serializable; import java.math.BigDecimal; public class AggregatedDepartment implements Serializable{ @SuppressWarnings("compatibility:5167698678781240729") private static final long serialVersionUID = 1L; private BigDecimal departmentId; private String departmentName; private BigDecimal sum; private BigDecimal avg; private BigDecimal max; private BigDecimal min; public AggregatedDepartment() { super(); } public AggregatedDepartment(BigDecimal departmentId, String departmentName, BigDecimal sum, BigDecimal avg, BigDecimal max, BigDecimal min) { super(); this.departmentId = departmentId; this.departmentName = departmentName; this.sum = sum; this.avg = avg; this.max = max; this.min = min; } public void setDepartmentId(BigDecimal departmentId) { this.departmentId = departmentId; } public BigDecimal getDepartmentId() { return departmentId; } public void setDepartmentName(String departmentName) { this.departmentName = departmentName; } public String getDepartmentName() { return departmentName; } public void setSum(BigDecimal sum) { this.sum = sum; } public BigDecimal getSum() { return sum; } public void setAvg(BigDecimal avg) { this.avg = avg; } public BigDecimal getAvg() { return avg; } public void setMax(BigDecimal max) { this.max = max; } public BigDecimal getMax() { return max; } public void setMin(BigDecimal min) { this.min = min; } public BigDecimal getMin() { return min; } } 7. Create the util java class called JavaBeanResult. The function of this class is to configure a native SQL query to return POJOs in a single line of code using the utility class. Credits: http://onpersistence.blogspot.com.br/2010/07/eclipselink-jpa-native-constructor.html package oramag.sample.dashboard.model.util; /******************************************************************************* * Copyright (c) 2010 Oracle. All rights reserved. * This program and the accompanying materials are made available under the * terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0 * which accompanies this distribution. * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html * and the Eclipse Distribution License is available at * http://www.eclipse.org/org/documents/edl-v10.php. * * @author shsmith ******************************************************************************/ import java.lang.reflect.Constructor; import java.lang.reflect.InvocationTargetException; import java.util.ArrayList; import java.util.List; import javax.persistence.Query; import org.eclipse.persistence.exceptions.ConversionException; import org.eclipse.persistence.internal.helper.ConversionManager; import org.eclipse.persistence.internal.sessions.AbstractRecord; import org.eclipse.persistence.internal.sessions.AbstractSession; import org.eclipse.persistence.jpa.JpaHelper; import org.eclipse.persistence.queries.DatabaseQuery; import org.eclipse.persistence.queries.QueryRedirector; import org.eclipse.persistence.sessions.Record; import org.eclipse.persistence.sessions.Session; /*** * This class is a simple query redirector that intercepts the result of a * native query and builds an instance of the specified JavaBean class from each * result row. The order of the selected columns musts match the JavaBean class * constructor arguments order. * * To configure a JavaBeanResult on a native SQL query use: * JavaBeanResult.setQueryResultClass(query, SomeBeanClass.class); * where query is either a JPA SQL Query or native EclipseLink DatabaseQuery. * * @author shsmith * */ public final class JavaBeanResult implements QueryRedirector { private static final long serialVersionUID = 3025874987115503731L; protected Class resultClass; public static void setQueryResultClass(Query query, Class resultClass) { JavaBeanResult javaBeanResult = new JavaBeanResult(resultClass); DatabaseQuery databaseQuery = JpaHelper.getDatabaseQuery(query); databaseQuery.setRedirector(javaBeanResult); } public static void setQueryResultClass(DatabaseQuery query, Class resultClass) { JavaBeanResult javaBeanResult = new JavaBeanResult(resultClass); query.setRedirector(javaBeanResult); } protected JavaBeanResult(Class resultClass) { this.resultClass = resultClass; } @SuppressWarnings("unchecked") public Object invokeQuery(DatabaseQuery query, Record arguments, Session session) { List results = new ArrayList(); try { Constructor[] constructors = resultClass.getDeclaredConstructors(); Constructor javaBeanClassConstructor = null; // (Constructor) resultClass.getDeclaredConstructors()[0]; Class[] constructorParameterTypes = null; // javaBeanClassConstructor.getParameterTypes(); List rows = (List) query.execute( (AbstractSession) session, (AbstractRecord) arguments); for (Object[] columns : rows) { boolean found = false; for (Constructor constructor : constructors) { javaBeanClassConstructor = constructor; constructorParameterTypes = javaBeanClassConstructor.getParameterTypes(); if (columns.length == constructorParameterTypes.length) { found = true; break; } // if (columns.length != constructorParameterTypes.length) { // throw new ColumnParameterNumberMismatchException( // resultClass); // } } if (!found) throw new ColumnParameterNumberMismatchException( resultClass); Object[] constructorArgs = new Object[constructorParameterTypes.length]; for (int j = 0; j < columns.length; j++) { Object columnValue = columns[j]; Class parameterType = constructorParameterTypes[j]; // convert the column value to the correct type--if possible constructorArgs[j] = ConversionManager.getDefaultManager() .convertObject(columnValue, parameterType); } results.add(javaBeanClassConstructor.newInstance(constructorArgs)); } } catch (ConversionException e) { throw new ColumnParameterMismatchException(e); } catch (IllegalArgumentException e) { throw new ColumnParameterMismatchException(e); } catch (InstantiationException e) { throw new ColumnParameterMismatchException(e); } catch (IllegalAccessException e) { throw new ColumnParameterMismatchException(e); } catch (InvocationTargetException e) { throw new ColumnParameterMismatchException(e); } return results; } public final class ColumnParameterMismatchException extends RuntimeException { private static final long serialVersionUID = 4752000720859502868L; public ColumnParameterMismatchException(Throwable t) { super( "Exception while processing query results-ensure column order matches constructor parameter order", t); } } public final class ColumnParameterNumberMismatchException extends RuntimeException { private static final long serialVersionUID = 1776794744797667755L; public ColumnParameterNumberMismatchException(Class clazz) { super( "Number of selected columns does not match number of constructor arguments for: " + clazz.getName()); } } } 8. Create the DataControl and a jsf or jspx page 9. Drag allDepartmentsHavingEmployees from DataControl and drop in your page 10. Choose Graph > Type: Bar (Normal) > any layout 11. In the wizard screen, Bars label, adds: sum, avg, max, min. In the X Axis label, adds: departmentName, and click in OK button 12. Run the page, the result is showed below: You can download the workspace here . It was using the latest jdeveloper version 11.1.2.2.

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  • how can i unmarshall in jaxb and enjoy the schema validation without using an explicit schema file

    - by ekeren
    I am using jaxb for my application configurations I feel like I am doing something really crooked and I am looking for a way to not need an actual file or this transaction. As you can see in code I: 1.create a schema into a file from my JaxbContext (from my class annotation actually) 2.set this schema file in order to allow true validation when I unmarshal JAXBContext context = JAXBContext.newInstance(clazz); Schema mySchema = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI).newSchema(schemaFile); jaxbContext.generateSchema(new MySchemaOutputResolver()); // ultimately creates schemaFile Unmarshaller u = m_context.createUnmarshaller(); u.setSchema(mySchema); u.unmarshal(...); do any of you know how I can validate jaxb without needing to create a schema file that sits in my computer? Do I need to create a schema for validation, it looks redundant when I get it by JaxbContect.generateSchema ? How do you do this?

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  • Why does this explicit call of a Scala method allow it to be implicitly resolved?

    - by Matt R
    Why does this code fail to compile, but compiles successfully when I uncomment the indicated line? (I'm using Scala 2.8 nightly). It seems that explicitly calling string2Wrapper allows it to be used implicitly from that point on. class A { import Implicits.string2Wrapper def foo() { //string2Wrapper("A") ==> "B" // <-- uncomment } def bar() { "A" ==> "B" "B" ==> "C" "C" ==> "D" } object Implicits { implicit def string2Wrapper(s: String) = new Wrapper(s) class Wrapper(s: String) { def ==>(s2: String) {} } } }

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  • Should you correct compiler warnings about type conversions using explicit typecasts?

    - by BastiBechtold
    In my current project, the compiler shows hundreds of warnings about type conversions. There is a lot of code like this iVar = fVar1*fVar2/fVar3; // or even iVar = fVar1*fVar2/fVar3+.5f; which intentionally assign float values to int. Of course, I could fix these warnings using iVar = int(...); but that looks kind of ugly. Would you rather live with the ugliness or live with the warnings? Or is there even a clean solution?

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  • Can I grant explicit Javascript methods to a different-host iframe?

    - by Matchu
    I'm thinking about a system in which I allow users to create Javascript-empowered widgets for other users to embed in their dashboard on my website. I'd like to limit these widgets fairly strictly, so each would exist as an iframe kept on its own unique hostname: the widget with ID #47 would be accessible at w47.widgets.example.com, for example. It would be helpful, for permission-granting dialogs and the like, to allow the widget to call very specific methods explicitly granted by the parent window, without authorizing the iframe to do whatever it likes with the parent frame on the user's behalf. Is it possible for a parent document to explicitly allow certain method calls to a child document on a different host?

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  • What if I made an explicit reference to 'this' for use inside an inner class?

    - by badp
    So far, I've used this approach to access this from the scope of an inner class: class FooManagementWindow extends JFrame { JButton rejectFoo; //... void getFooAcceptingPanel(){ //... final FooManagementWindow referenceToThis = this; rejectFoo = new JButton("Reject"); rejectFoo.addEventListener(new EventListener() { @Override public void actionPerformed(ActionEvent arg) { referenceToThis.setEnabled(false); //this requires a network call //... referenceToThis.setEnabled(true); //the user may resume his work } }); //... } } However, I just learned that instead of declaring referenceToThis, a direct reference is kept for me as: FooManagementWindow.this I have no reason to think my less standard approach may lead to errors or weird corner cases. Or are there?

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  • JavaScript Class Patterns Revisited: Endgame

    - by Liam McLennan
    I recently described some of the patterns used to simulate classes (types) in JavaScript. But I missed the best pattern of them all. I described a pattern I called constructor function with a prototype that looks like this: function Person(name, age) { this.name = name; this.age = age; } Person.prototype = { toString: function() { return this.name + " is " + this.age + " years old."; } }; var john = new Person("John Galt", 50); console.log(john.toString()); and I mentioned that the problem with this pattern is that it does not provide any encapsulation, that is, it does not allow private variables. Jan Van Ryswyck recently posted the solution, obvious in hindsight, of wrapping the constructor function in another function, thereby allowing private variables through closure. The above example becomes: 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()); Now we have prototypal inheritance and encapsulation. The important thing to understand is that the constructor, and the toString function both have access to the name and age private variables because they are in an outer scope and they become part of the closure.

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  • TypeError: Error #1007: Instantiation attempted on a non-constructor. on port to Flex 4

    - by Josh Handel
    I have been porting an app from Flex 3.4.x to 4.0.. I have successfully ported the app and its libraries to flex 4.0, I've also removed ALL the references to http://www.adobe.com/2006/flex/mx in any of my mxml files... In short I "think" I have moved everything over to the new mx framework (2009).. But I still get the following error (which never happend in 3.4 or 3.5 with this same app) when I try to run my flex app. TypeError: Error #1007: Instantiation attempted on a non-constructor. at mx.preloaders::Preloader/initialize()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\preloaders\Preloader.as:253] at mx.managers::SystemManager/http://www.adobe.com/2006/flex/mx/internal::initialize()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\SystemManager.as:1925] at mx.managers::SystemManager/initHandler()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\SystemManager.as:2419] At this point I am completely stumped.. anyone have any ideas? Thanks

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