public fields - Page 425

Custom business object comparer

- by gruber

Hello, I need to implement mechanism that compares two business objects and return the list of differences (past value, new value, isDifferenceBetter). Because not all fields of class has to be compared and one fields need to be compared with different function then the other (sometimes < is better sometimes is better ... ) I figured out that I need to implelemnt custom attribute and give it to each field that has to be compared in this object. This attribute must have: - name - delegate or sth to point to the function which would be applied for comparision (dont know how to do it so far) So could anyone suggest me if its a good idea? Maybe any other ideas. Using attributes I would be able to use refflection to iterate through each field with attribute and invoke needed delegate. thanks for help bye

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How do you override operator == when using interfaces instead of actual types?

- by RickL

I have some code like this: How should I implement the operator == so that it will be called when the variables are of interface IMyClass? public class MyClass : IMyClass { public static bool operator ==(MyClass a, MyClass b) { if (ReferenceEquals(a, b)) return true; if ((Object)a == null || (Object)b == null) return false; return false; } public static bool operator !=(MyClass a, MyClass b) { return !(a == b); } } class Program { static void Main(string[] args) { IMyClass m1 = new MyClass(); IMyClass m2 = new MyClass(); MyClass m3 = new MyClass(); MyClass m4 = new MyClass(); Console.WriteLine(m1 == m2); // does not go into custom == function. why not? Console.WriteLine(m3 == m4); // DOES go into custom == function } }

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Pattern for database-wrapper in java

- by Space_C0wb0y

I am currently writing a java-class that wraps an SQLite database. This class has two ways to be instantiated: Open an existing database. Create a new database. This is what I cam up with: public class SQLiteDatabaseWrapper { public static SQLiteDatabaseWrapper openExisting(File PathToDB) { return new SQLiteDatabaseWrapper(PathToDB); } public static SQLiteDatabaseWrapper createNew(File PathToDB) { CreateAndInitializeNewDatabase(PathToDB); return new SQLiteDatabaseWrapper(PathToDB); } private SQLiteDatabaseWrapper(File PathToDB) { // Open connection and setup wrapper } } Is this the way to go in Java, or is there any other best practice for this situation?

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Java Thread - Synchronization issue

- by Yatendra Goel

From Sun's tutorial: Synchronized methods enable a simple strategy for preventing thread interference and memory consistency errors: if an object is visible to more than one thread, all reads or writes to that object's variables are done through synchronized methods. (An important exception: final fields, which cannot be modified after the object is constructed, can be safely read through non-synchronized methods, once the object is constructed) This strategy is effective, but can present problems with liveness, as we'll see later in this lesson. Q1. Is the above statements mean that if an object of a class is going to be shared among multiple threads, then all instance methods of that class (except getters of final fields) should be made synchronized, since instance methods process instance variables?

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Time diff calculations where date and time are in seperate columns

- by pedalpete

I've got a query where I'm trying to get the hours in duration (eg 6.5 hours) between two different times. In my database, time and date are held in different fields so I can efficiently query on just a startDate, or endDate as I never query specifically on time. My query looks like this SELECT COUNT(*), IFNULL(SUM(TIMEDIFF(endTime,startTime)),0) FROM events WHERE user=18 Sometimes an event will go overnight, so the difference between times needs to take into account the differences between the dates as well. I've been trying SELECT COUNT(*), IFNULL(SUM(TIMEDIFF(CONCAT(endDate,' ',endTime),CONCAT(startDate,' ',startTime))),0) FROM events WHERE user=18 Unfortunately I only get errors when I do this, and I can't seem to combine the two fields into a single timestamp.

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Why wasn't C# designed with 'const' for variables and methods?

- by spoulson

I suspect const was simplified for the C# spec for general language simplicity. Was there a specific reason we can't declare variable references or methods as const like we can with C++? e.g.: const MyObject o = new MyObject(); // Want const cast referenece of MyObject o.SomeMethod(); // Theoretically legal because SomeMethod is const o.ChangeStuff(); // Theoretically illegal because ChangeStuff is not const class MyObject { public int val = 0; public void SomeMethod() const { // Do stuff, but can't mutate due to const declaration. } public void ChangeStuff() { // Code mutates this instance. Can't call with const reference. val++; } }

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How can I redirect the stdout of ironpython in C#?

- by Begtostudy

public partial class Form1 : Form { public Form1() { InitializeComponent(); } private void button3_Click(object sender, EventArgs e) { try { var strExpression = @" import sys sys.stdout=my.write print 'ABC' "; var engine = Python.CreateEngine(); var scope = engine.CreateScope(); var sourceCode = engine.CreateScriptSourceFromString(strExpression); scope.SetVariable("my", this); var actual = sourceCode.Execute(scope); textBox1.Text += actual; } catch (System.Exception ex) { MessageBox.Show(ex.ToString()); } } public void write(string s) { textBox1.Text += s; } }<code> But Exception says there is not write. Where is wrong? Thanks!

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Dynamically add annotation to an existing class

- by ng

I have the following class public class Person { ... } I would like to create another class that would look like this. @SomeAnnotation public class Person { ... } Via a simple method like so. public static Class addAnnotation(Class originalType, Class<? extends Annotation> annotation) { // what goes here? } Is there an easy way to do this via ASM for example? What dependencies would I need. I have tried to Google this however the examples I have found are either incomplete or are doing something else. Other frameworks such as javassist would be just as good.

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I'm new to Java most basic question about arrays!

- by ambidextorous

Hey I have not been able to find a proper answer on any forums about this but how exactly do I pass an array to a class? public class TestArray { String name; String[] array; public TestArray(String name, String[] anArray){ this.name = name; int len = anArray.length; this.array = new String[len]; for (int i = 0; i < len; i++){ this.array[i] = new String(anArray[i]); } } } public static void main(String[] args){ String[] anArray = new String[2]; anArray[0] = new String("Test"); anArray[1] = new String("Test2"); TestArray work = new TestArray("Jordan", anArray?); } }

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Java Enum Newbie Question

- by ikurtz

i have a situation where i need the Checker enum below used in multiple classes: package Sartre.Connect4; public enum Checker { EMPTY, RED, YELLOW } so i put the Checker in a Checker.java file and then from the classes that need it i simply do the following: example: public Cell(){ currentCell = Checker.EMPTY; } example: public Cell(Checker checker){ currentCell = checker; } and the code compiles fine and runs fine also. so what is my question? well being new to Java i am just wondering if the way i use Checker without encapsulating it in a class is a sound implementation? it may be because of The enum declaration defines a class (called an enum type). as noted in Java docs enum tutorial page. thank you for your insight into this matter.

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Check if a class is subclass of another class in Java

- by craesh

Hi! I'm playing around with Java's reflection API and trying to handle some fields. Now I'm stuck with identifying the type of my fields. Strings are easy, just do myField.getType().equals(String.class). The same applies for other non-derived classes. But how do I check derived classes? E.g. LinkedList as subclass of List. I can't find any isSubclassOf(...) or extends(...) method. Do I need to walk through all getSuperClass() and find my supeclass by my own? Thanks! craesh

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Unit Testing: hard dependency MessageBox.Show()

- by Sean B

What ways can the SampleConfirmationDialog be unit tested? The SampleConfirmationDialog would be exercised via acceptance tests, however how could we unit test it, seeing as MessageBox is not abstract and no matching interface? public interface IConfirmationDialog { /// <summary> /// Confirms the dialog with the user /// </summary> /// <returns>True if confirmed, false if not, null if cancelled</returns> bool? Confirm(); } /// <summary> /// Implementation of a confirmation dialog /// </summary> public class SampleConfirmationDialog : IConfirmationDialog { /// <summary> /// Confirms the dialog with the user /// </summary> /// <returns>True if confirmed, false if not, null if cancelled</returns> public bool? Confirm() { return MessageBox.Show("do operation x?", "title", MessageBoxButton.YesNo, MessageBoxImage.Question) == MessageBoxResult.Yes; } }

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How can I get around MySQL Errcode 13 with SELECT INTO OUTFILE?

- by Ryan Olson

but I am trying to dump the contents of a table to a csv file using a MySQL SELECT INTO OUTFILE statement. If I do: SELECT column1, column2 INTO OUTFILE 'outfile.csv' FIELDS TERMINATED BY ',' FROM table_name; outfile.csv will be created on the server in the same directory this database's files are stored in. However, when I change my query to: SELECT column1, column2 INTO OUTFILE '/data/outfile.csv' FIELDS TERMINATED BY ',' FROM table_name; I get: ERROR 1 (HY000): Can't create/write to file '/data/outfile.csv' (Errcode: 13) Errcode 13 is a permissions error, even if I change ownership of /data to mysql:mysql and give it 777 permissions. MySQL is running as user "mysql". Strangely, I can create the file in /tmp, just not in any other directory I've tried, even with permissions set such that user mysql should be able to write to the directory. This is MySQL 5.0.75 running on Ubuntu.

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Can this be done with multiple inhertance?

- by Milo

Here is what I would like to do. Say I have Class Widget. I then create Button from Widget. I then create ModifiedWidget which re-implements certain functions of Widget. I then want Button to use ModifiedWidget rather than plain Widget. Is this possible to do some how? Thanks class Button : public Widget; class SuperButton : public Button, public ModifiedWidget; I'm just not sure if that would do what I want it to though.

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ASP.Net navigation tabs like windows tab control

- by devphil

I would like to have a webpage something like windows tab control. Each webpage does not lose the contents and data while moving between pages, postbacks, etc. Here is the website design and my idea: [Master Page] "Fruits" "Cars" "Animals" "Operators" clicking on "Fruits" will forwards to "Fruits" page, and the same for other links (tabs) The user works on "Fruits" page searching fruits, fill up some fields, etc. The user then moves to "Cars" page and then builds up his own car by filling some fields, etc and then the user goes back to "Fruits" page again - the user sees the same page where she/he left on "Fruits" page. Please suggest some good ways other than using javascript:history.go(-1). Is this possible to implement?

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Why has to be size of dynamically-allocated array a static field?

- by Ondrej Slinták

I have a dummy class where I am testing arrays. I've noticed that when I want to dynamically allocate size of array at runtime, fields that indicate this size have to be static. I know I should probably use collections for this kind of code, but I'm more interested why do these fields have to be static? Is there any particular reason behind this? class Foo { private static int x; private static int y; private int[,] bar = new int[ x, y ]; public Foo( int a, int b ) { x = a; y = b; } }

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Visual-C++ Linker Error

- by LordByron

I have a class called MODEL in which public static int theMaxFrames resides. The class is defined in its own header file. theMaxFrames is accessed by a class within the MODEL class and by one function, void set_up(), which is also in the MODEL class. The Render.cpp source file contains a function which calls a function in the Direct3D.cpp source file which in turn calls the set_up() function through a MODEL object. This is the only connection between these two source files and theMaxFrames. When I try to compile my code I get the following error messages: 1Direct3D.obj : error LNK2001: unresolved external symbol "public: static int MODEL::theMaxFrames" (?theMaxFrames@MODEL@@2HA) 1Render.obj : error LNK2001: unresolved external symbol "public: static int MODEL::theMaxFrames" (?theMaxFrames@MODEL@@2HA) 1C:\Users\Byron\Documents\Visual Studio 2008\Projects\xFileViewer\Debug\xFileViewer.exe : fatal error LNK1120: 1 unresolved externals

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Simple Question:Output of below Java program

- by Abhishek Jain

public class abc1 { private String s; public abc1(String s){this.s=s;} public static void main(String args[]) { HashSet<Object> hs=new HashSet<Object>(); abc1 a1= new abc1("abc"); abc1 a2= new abc1("abc"); String s1= new String("abc"); String s2= new String("abc"); hs.add(a1); hs.add(a2); hs.add(s1); hs.add(s2); System.out.println(hs.size()); } } Why above program output is 3?

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Cakephp beforeFind() - How do I add a JOIN condition AFTER the belongsTo association is added?

- by michael

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non-scalar type requested

- by lego69

can somebody please help me with an error conversion from `A' to non-scalar type `B' requested I have class A and derived from it B, but I have problems with these rows: A a(1); A *pb = new B(a); B b = *pb; //here I have an error thanks in advance for any help class A { protected: int player; public: A(int initPlayer = 0); A(const A&); A& operator=(const A&); virtual ~A(){}; virtual void foo(); void foo() const; operator int(); }; class B: public A { public: B(int initPlayer): A(initPlayer){}; ~B(){}; virtual void foo(); };

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Get Item from Collection by unique ID

- by David Murdoch

I have a collection of Contacts that inherits from CollectionBase: public class ContactCollection : CollectionBase{ //... } each contact in the collection has a unique ID: public class Contact{ public int ContactID{ get; private set; } //... } I think what I would like to do is something like the following: // get the contact by their unique [Contact]ID Contact myPerson = Contact.GetContactById(15); // get all contacts for the customer ContactCollection contacts = customer.GetContacts(); // replaces the contact in the collection with the // myPerson contact with the same ContactID. contacts.ReplaceAt(myPerson); // saves the changes to the contacts and the customer // customer.Save(); There is probably a better way...if so, please suggest it.

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Clean way in GWT/Java to wait for multiple asynchronous events to finish

- by gerdemb

What is the best way to wait for multiple asynchronous callback functions to finish in Java before continuing. Specifically I'm using GWT with AsyncCallback, but I think this is a generic problem. Here's what I have now, but surely there is cleaner way... AjaxLoader.loadApi("books", "0", new Runnable(){ public void run() { bookAPIAvailable = true; ready(); }}, null); AjaxLoader.loadApi("search", "1", new Runnable(){ public void run() { searchAPIAvailable = true; ready(); }}, null); loginService.login(GWT.getHostPageBaseURL(), new AsyncCallback<LoginInfo>() { public void onSuccess(LoginInfo result) { appLoaded = true; ready(); } }); private void ready() { if(bookAPIAvailable && searchAPIAvailable && appLoaded) { // Everything loaded } }

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how can we call one class's method through another class's object in php

- by hello

I want to know that is there any method in PHP by which i can call one class's method from another class object. let me clear here is one class class A() { public function showData(){ //here is method of class A } } // here is another class class B(){ public function getData(){ //some method in class B } } //now i create two objects $objA= new class A(); $objB=new class B(); now i want to call this $objB->showData();<--- is that possible .. by any how method( using public, inheritence,child parent etc...) please help me

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One table for uploads for multiple resources in CakePHP

- by Mef

Hi, I have CakePHP app in which I'd like to attach gallery to multiple resources. Let's say I've got artists, each one has own gallery. I've got articles, every article has some images attached to it and so on. Now I set up tables like this: Artists hasMany Artistimages, fields in artistimages table are: id, artist_id, filename, filetype, filesize etc. Articles hasMany Articleimages, fields in articleimages table are: id, article_id, filename, filetype, filesize etc. ...but this is not how it should be, I think. Is there possibility to have one table called for example uploads which will contain all images with foreign key pointing to resource its reffering to? How to tell CakePHP which image is coming from which resource?

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Class declaration bug (NoClassDefFoundError caused by ClassNotFoundException)

- by aladine

Please advise me what's wrong with this class declaration: ExchEngine.java package engine; public class ExchEngine { public ExchEngine() { } public static void main(String[] args) { ExchEngine engine=new ExchEngine() ; } } When I compile this file, I always get exception: java.lang.NoClassDefFoundError: test_engine/ExchEngine Caused by: java.lang.ClassNotFoundException: test_engine.ExchEngine at java.net.URLClassLoader$1.run(URLClassLoader.java:202) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:190) at java.lang.ClassLoader.loadClass(ClassLoader.java:307) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) at java.lang.ClassLoader.loadClass(ClassLoader.java:248) Exception in thread "main" This seems very weird that ExchEngine.java is inside a package and it cannot run itself. Thanks for any help.

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