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• In java can i have more than one class/object in a file?

  - by David

  So the way i've been told to do things is you have your file and the file name is Classname.java and then the code is something like this: class ClassName { SOME METHODS main {} } and then thats all. I'd like to have two objects defined and used within the same .java file. (i don't want to have to put the other class in a difernt file just because i'd like to send this to someone and i want to avoid hasstle of atatching multiple files to an email [the lazy do make good programers though if you think about it]) is it possible to do this? do i have to do anything special and if so what? what are some mistakes i'm likely to make or that you have made in the past when doing this?

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• Appengine Model SelfReferenceProperty and parent child relationship

  - by GeekTantra

  I have a scenario in which I need a self reference property as follow: class Post(db.Model): creator = db.UserProperty() post_title = db.StringProperty(required=True) post_status = db.StringProperty(required=True, choices=['draft', 'published']) post_parent = db.SelfReferenceProperty() Now, I want ensure that an entity shouldn't be its own parent and a child of an entity cannot be its parent. How can I ensure this kind of a relationship in the PostForm model form and the Post model.

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• ModelName(django.contrib.auth.models.User) vs ModelName(models.Model)

  - by amr.negm

  I am developing a django project. I created some apps, some of those are related to User model, for instance, I have a feeds app that handles user feeds, and another app that deals with extra user data like age, contacts, and friends. for each of these, I created a table that should be connected to the User model, which I using for storing and authenticating users. I found two ways to deal with this issue. One, is through extending User model to be like this: ModelName(User): friends = models.ManyToMany('self') ..... Two, is through adding a foreign key to the new table like this: ModelName(models.Model): user = models.ForeignKey(User, unique=True) friends = friends = models.ManyToMany('self') ...... I can't decide which to use in which case. in other words, what are the core differences between both?

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• C# Dynamic Query Without A Database Model

  - by hitopp

  I have been searching the web for a solution to dynamic queries. I have found many different solutions (e.g. Linq to Sql, Dynamic Linq Expressions, Dynamic Query), but all of these solutions involve some sort of previous knowledge of the database (like a model in code). Maybe what I am asking is way off the deep end, but is there any possible way to dynamically query a database without a model? For example, a database has a Customers table with the following columns: CustomerID Name FavoriteColor I want to create a query as SELECT Name FROM Customers WHERE @0 = @1, where the two placeholders are populated dynamically. The resulting data does not tie to a model class and I would prefer to use some sort of framework to build the queries, not simple string concatenation. The System.Linq.Dynamic namespace came really close to fulfilling this request, but it uses a database model. I realize this is crazy, but I was just curious.

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• What is the use of Method Overloading in Java when it is achieved by changing the sequence of parameters in the argument list?

  - by MediumOne

  I was reading a Java training manual and it said that Method Overloading in Java can be achieved by having a different argument list. It also said that the argument list could differ in (i). Number of parameters (ii). Datatype of parameters (iii). Sequence of parameters My concern is about (iii). What is the use of trying to overload a method just by changing the sequence of parameters? I am unable to think of any benefits by this way.

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• Is there a Java unit-test framework that auto-tests getters and setters?

  - by Michael Easter

  There is a well-known debate in Java (and other communities, I'm sure) whether or not trivial getter/setter methods should be tested. Usually, this is with respect to code coverage. Let's agree that this is an open debate, and not try to answer it here. There have been several blog posts on using Java reflection to auto-test such methods. Does any framework (e.g. jUnit) provide such a feature? e.g. An annotation that says "this test T should auto-test all the getters/setters on class C, because I assert that they are standard". It seems to me that it would add value, and if it were configurable, the 'debate' would be left as an option to the user.

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• Django updating a single model

  - by Hellnar

  Hello How can I use the update() method on a single model which I retrieved via Queryset.get() ? It seems like model. Model doesn't have an update() method yet I cannot invoke .save() as I have a pre-save signals which messes things up. EDIT: An idea would be passing some parameter to the save method and catching it at the pre_save signal, so that I can understand the purpose, how can this be done ? Thanks

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• Best approach to creating a database driven Java website?

  - by Craig Whitley

  I'm fairly new to programming and new to java, but I'd like to jump in the deep end with a little database driven website project. I've read quite a lot about requirements in the 'real world' requesting experience with Spring and Hibernate, so I have those installed on netbeans and a project created (if I hit run I get the default spring page). Now I just need a little guidance as to where to start designing my app (please tell me if I'm getting in a bit too over my head for a beginner!). Should I start off with my classes? - create all my classes as they map to my database tables and decide which attributes and methods each will require? Can anyone suggest any good books for maybe.. making a java based website from scratch (i.e. from design right through to deployment) that might be useful for a beginner? Any help appreciated thanks.

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• Why do Java and C# not have implicit conversions to boolean?

  - by Shaun

  Since I started Java it's been very aggravating for me that it doesn't support implicit conversions from numeric types to booleans, so you can't do things like: if (flags & 0x80) { ... } instead you have to go through this lunacy: if ((flags & 0x80) != 0) { ... } It's the same with null and objects. Every other C-like language I know including JavaScript allows it, so I thought Java was just moronic, but I've just discovered that C# is the same (at least for numbers, don't know about null/objects): http://msdn.microsoft.com/en-us/library/c8f5xwh7(VS.71).aspx Microsoft changed it on purpose from C++, so why? Clearly I'm missing something. Why change (what I thought was) the most natural thing in the world to make it longer to type? What on Earth is wrong with it?

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• codeigniter - pass all form values to model

  - by Patrick

  I have a registration form that collects several parameters. i need to pass all these AND a confirmation code (generated by the controller) to the model for inserting in the DB. How can I do that? is there a way to pass the whole post to the model, eg like $this->model->insert($this->input->form(), $confirmation_code)?

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• Which low level tasks can be accomplished on the JVM, but not expressed in java?

  - by mike g

  Which useful (for performance or otherwise) constructions are valid bytecode, but not expressable in Java?

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• In Java, how do I set a return type if an exception occurs?

  - by beagleguy

  hey all, I'm new to Java and was wondering if I define a method to return a database object like import java.sql.*; public class DbConn { public Connection getConn() { Connection conn; try { Class.forName("com.mysql.jdbc.Driver").newInstance(); if(System.getenv("MY_ENVIRONMENT") == "development") { String hostname = "localhost"; String username = "root"; String password = "root"; } conn = DriverManager.getConnection("jdbc:mysql:///mydb", username, password); return conn; } catch(Exception e) { throw new Exception(e.getMessage()); } } } if the connection fails when I try to create it what should I return? eclipse is telling me I have to return a Connection object but if it fails I'm not sure what to do. thanks!

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• How can I disable a model field in a django form

  - by jammon

  I have a model like this: class MyModel(models.Model): REGULAR = 1 PREMIUM = 2 STATUS_CHOICES = ((REGULAR, "regular"), (PREMIUM, "premium")) name = models.CharField(max_length=30) status = models.IntegerField(choices = STATUS_CHOICES, default = REGULAR) class MyForm(forms.ModelForm): class Meta: model = models.MyModel In a view I initialize one field and try to make it non-editable: myform = MyForm(initial = {'status': requested_status}) myform.fields['status'].editable = False But the user can still change that field. What's the real way to accomplish what I'm after?

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• What is the most efficient algorithm for reversing a String in Java?

  - by Hultner

  I am wondering which way to reverse a string in Java that is most efficient. Should I use some sort of xor method? The easy way would be to put all the chars in a stack and put them back into a string again but I doubt that's a very efficient way to do it. And please do not tell me to use some built in function in Java. I am interested in learning how to do it not to use an efficient function but not knowing why it's efficient or how it's built up.

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• Convert a string representation of a hex dump to a byte array using Java?

  - by ravigad

  I am looking for a way to convert a long string (from a dump), that represents hex values into a byte array. I couldn't have phrased it better than the person that posted the same question here: http://www.experts-exchange.com/Programming/Programming_Languages/Java/Q_21062554.html But to keep it original, I'll phrase it my own way: suppose I have a string "00A0BF" that I would like interpreted as the byte[] {0x00,0xA0,0xBf} what should I do? I am a Java novice and ended up using BigInteger and watching out for leading hex zeros. But I think it is ugly and I am sure I am missing something simple...

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• What's the best way to replace the first letter of a string in Java?

  - by froadie

  I'm trying to convert the first letter of a string to lowercase. I know there's a capitalize method, but I want to accomplish the opposite. This is the code I used: value.substring(0,1).toLowerCase() + value.substring(1) Effective, but feels a bit manual. Are there any other ways to do it? Any better ways? Any Java string functions that do it for you? I was thinking of using something like a replace function, but Java's replace doesn't accept an index as a parameter. You have to pass the actual character/substring. Another way I can think of doing it is something like: value.replaceFirst(value.charAt(0), value.charAt(0).toLowerCase()) Except that replaceFirst expects 2 strings, so the value.charAt(0)s would probably need to be replaced with value.substring(0,1)s. Is this any better? Does it matter? Is there any standard way to do this?

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• How to run Jersey with the built in web server from Java SE 6?

  - by Mike Petterson

  I don't want to use Tomcat, Jetty or an Java EE 6 container to offer REST services but the built in web server.

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• Why learn Perl, Python, Ruby if the company is using C++, C# or Java as the application language?

  - by szabgab

  I wonder why would a C++, C#, Java developer want to learn a dynamic language? Assuming the company won't switch its main development language from C++/C#/Java to a dynamic one what use is there for a dynamic language? What helper tasks can be done by the dynamic languages faster or better after only a few days of learning than with the static language that you have been using for several years? Update After seeing the first few responses it is clear that there two issues. My main interest would be something that is justifiable to the employer as an expense. That is, I am looking for justifications for the employer to finance the learning of a dynamic language. Aside from the obvious that the employee will have broader view, the employers are usually looking for some "real" benefit.

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• Which Java library lets me initialize an object's properties from a properties file?

  - by Kjetil Ødegaard

  Is there a Java library that lets you "deserialize" a properties file directly into an object instance? Example: say you have a file called init.properties: username=fisk password=frosk and a Java class with some properties: class Connection { private String username; private String password; public void setUsername(String username) { this.username = username; } public void setPassword(String password) { this.password = password; } } I want to do this: Connection c = MagicConfigurator.configure("init.properties", new Connection()) and have MagicConfigurator apply all the values from the properties file to the Connection instance. Is there a library with a class like this?

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• NSData means what? how to implements its characterstics in java?

  - by androidbase

  NSData means what? how to implements its characterstics in java?

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• Java program runs smoothly in Netbeans but slowly in Eclipse and as an executed jar. WTF?

  - by comp sci balla

  A java program that does frequent swing/awt painting animation (but nothing more advanced than g.fillOval(...)) runs at a consistent 60fps in Netbeans, and at about 6fps when ran in Eclipse or executed as a jar file from a unix terminal. The program was developed in Netbeans and is run-of-the-mill desktop application (not webstart or japplet or ...). This is occurring in Ubuntu 10 with java 1.6. How is this possible? The universe no longer makes sense to me.

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• Problems using the Razor model when creating my knockout ViewModel

  - by Emil Kantis

  I'm having problems with using the Model in a javascript call when setting up my knockout VM.. @model List<AdminGui.Models.Domain> <script src="http://ajax.aspnetcdn.com/ajax/knockout/knockout-2.2.1.js" type="text/javascript"></script> <script type="text/javascript"> function ViewModel() { var self = this; self.domains = ko.observableArray( ko.utils.arrayMap(@Model, function(item) { return new Domain(item.guid, item.description, item.namespaces); })); } I get a syntax error on @Model in the ko.utils.arrayMap call. I suspect it might be my Razor-fu that is lacking... :)

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• OpenGL "out of memory" on glReadPixels()

  - by spurserh

  Hello, I am running into an "out of memory" error from OpenGL on glReadPixels() under low-memory conditions. I am writing a plug-in to a program that has a robust heap mechanism for such situations, but I have no idea whether or how OpenGL could be made to use it for application memory management. The notion that this is even possible came to my attention through this [albeit dated] thread on a similar issue under Mac OS X: http://lists.apple.com/archives/Mac-opengl/2001/Sep/msg00042.html I am using Windows XP, and have seen it on multiple NVidia cards. I am also interested in any work-arounds I might be able to relay to users (the thread mentions "increasing virtual memory"). Thanks, Sean

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• Why Use java.lang.reflect.Array For Anything Other Than Array Creation?

  - by dimo414

  Java Class java.lang.reflect.Array provides a set of tools for creating an array dynamically. However in addition to that it has a whole set of methods for accessing (get, set, and length) an array. I don't understand the point of this, since you can (and presumably would) cast your dynamically generated array as an array upon creation, which means you can use the normal array access (bracket notation) functionality. In fact, looking at the source code you can see that is all the class does, cast the array, and throw an exception if the cast fails. So what's the point / usefulness of all of these extra methods?

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• Getting a random number between 0 and 0.06 in Java?

  - by podunk

  How do you get random Double values between 0.0 and 0.06 in Java?

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