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  • Using inheritance and polymorphism to solve a common game problem

    - by Barry Brown
    I have two classes; let's call them Ogre and Wizard. (All fields are public to make the example easier to type in.) public class Ogre { int weight; int height; int axeLength; } public class Wizard { int age; int IQ; int height; } In each class I can create a method called, say, battle() that will determine who will win if an Ogre meets and Ogre or a Wizard meets a Wizard. Here's an example. If an Ogre meets an Ogre, the heavier one wins. But if the weight is the same, the one with the longer axe wins. public Ogre battle(Ogre o) { if (this.height > o.height) return this; else if (this.height < o.height) return o; else if (this.axeLength > o.axeLength) return this; else if (this.axeLength < o.axeLength) return o; else return this; // default case } We can make a similar method for Wizards. But what if a Wizard meets an Ogre? We could of course make a method for that, comparing, say, just the heights. public Wizard battle(Ogre o) { if (this.height > o.height) return this; else if (this.height < o.height) return o; else return this; } And we'd make a similar one for Ogres that meet Wizard. But things get out of hand if we have to add more character types to the program. This is where I get stuck. One obvious solution is to create a Character class with the common traits. Ogre and Wizard inherit from the Character and extend it to include the other traits that define each one. public class Character { int height; public Character battle(Character c) { if (this.height > c.height) return this; else if (this.height < c.height) return c; else return this; } } Is there a better way to organize the classes? I've looked at the strategy pattern and the mediator pattern, but I'm not sure how either of them (if any) could help here. My goal is to reach some kind of common battle method, so that if an Ogre meets an Ogre it uses the Ogre-vs-Ogre battle, but if an Ogre meets a Wizard, it uses a more generic one. Further, what if the characters that meet share no common traits? How can we decide who wins a battle?

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  • Change spring bean properties at configuration time

    - by Nick Gerakines
    In a spring servlet xml file, I'm using org.springframework.scheduling.quartz.SchedulerFactoryBean to regularly fire a set of triggers. <bean class="org.springframework.scheduling.quartz.SchedulerFactoryBean"> <property name="triggers"> <list> <ref local="AwesomeTrigger" /> <ref local="GreatTrigger" /> <ref local="FantasticTrigger"/> </list> </property> </bean> The issue is that in different environments, I don't want certain triggers firing. Is there a way to include some sort of configuration or variable defined either in my build.properties for the environment or in a spring custom context properties file that assists the bean xml to determine which triggers should be included in the list? That way, for example, AwesomeTrigger would be called in development but not qa.

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  • How to avoid repetition when working with primitive types?

    - by I82Much
    I have the need to perform algorithms on various primitive types; the algorithm is essentially the same with the exception of which type the variables are. So for instance, /** * Determine if <code>value</code> is the bitwise OR of elements of <code>validValues</code> array. * For instance, our valid choices are 0001, 0010, and 1000. * We are given a value of 1001. This is valid because it can be made from * ORing together 0001 and 1000. * On the other hand, if we are given a value of 1111, this is invalid because * you cannot turn on the second bit from left by ORing together those 3 * valid values. */ public static boolean isValid(long value, long[] validValues) { for (long validOption : validValues) { value &= ~validOption; } return value != 0; } public static boolean isValid(int value, int[] validValues) { for (int validOption : validValues) { value &= ~validOption; } return value != 0; } How can I avoid this repetition? I know there's no way to genericize primitive arrays, so my hands seem tied. I have instances of primitive arrays and not boxed arrays of say Number objects, so I do not want to go that route either. I know there are a lot of questions about primitives with respect to arrays, autoboxing, etc., but I haven't seen it formulated in quite this way, and I haven't seen a decisive answer on how to interact with these arrays. I suppose I could do something like: public static<E extends Number> boolean isValid(E value, List<E> numbers) { long theValue = value.longValue(); for (Number validOption : numbers) { theValue &= ~validOption.longValue(); } return theValue != 0; } and then public static boolean isValid(long value, long[] validValues) { return isValid(value, Arrays.asList(ArrayUtils.toObject(validValues))); } public static boolean isValid(int value, int[] validValues) { return isValid(value, Arrays.asList(ArrayUtils.toObject(validValues))); } Is that really much better though? Any thoughts in this matter would be appreciated.

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  • Antlr MismatchedSetException During Interpretation

    - by user1646481
    I am new to Antlr and I have defined a basic grammar using Antlr 3. The grammar compiles and ANTLRWorks generates the Parser and Lexer code without any problems. The grammar can be seen below: grammar i; @header { package i; } module : 'Module1'| 'Module2'; object : 'I'; objectType : 'Name'; filters : EMPTY | 'WHERE' module; table : module object objectType; STRING : ('a'..'z'|'A'..'Z')+; EMPTY : ' '; The problem is that when I interpret the table Parser I get a MismatchedSetException. This is due to having the EMPTY. As soon as I remove EMPTY from the grammar, the interpretation works. I have looked on the Antlr website and some other examples and the Empty space is ' '. I am not sure what to do. I need this EMPTY. As soon as I change the EMPTY to be the following: EMPTY : ''; instead of: EMPTY : ' '; It actually interprets it. However, I am getting the following Exception: Interpreting... [10:57:23] problem matching token at 1:4 NoViableAltException(' '@[1:1: Tokens : ( T__4 | T__5 | T__6 | T__7 | T__8 | T__9 | T__10 | T__11 | T__12 | T__13 | T__14 | T__15 | T__16 );]) [10:57:23] problem matching token at 1:9 NoViableAltException(' '@[1:1: Tokens : ( T__4 | T__5 | T__6 | T__7 | T__8 | T__9 | T__10 | T__11 | T__12 | T__13 | T__14 | T__15 | T__16 );]) When I take out the EMPTY, there are no problems at all. I hope you can help.

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  • Is javac enough to build an OSGi bundle?

    - by Chatanga
    To produce a bundle from source using a tool such as javac, you need to provide it with a linear classpath. Unfortunately, it won't work in some situations still perfectly legal from an OSGi point of view: dependencies with embedded JAR in them; same packages contained by different dependencies. Since javac doesn't understand OSGi metadata, I won't be able to simply but the dependencies in a classpath. A finer package grained approach seems necessary. How this problem is addressed by people using OSGi in an automated process (continuous integration)? Strangely, there is a lot of resources on the web on how to create bundle JAR (creating the metadata, creating the JAR) provided you have the classes/inner JAR to put inside, but very few things on how actually get theses classes compiled.

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  • Grails , how do I get an object NOT to save

    - by user350325
    Hello I am new to grails and trying to create a form which allows a user to change the email address associated with his/her account for a site I am creating. It asks for the user for their current password and also for the new email address they want to use. If the user enters the wrong password or an invalid email address then it should reject them with an appropriate error message. Now the email validation can be done through constraints in grails, but the password change has to match their current password. I have implemented this check as a method on a service class. See code below: def saveEmail = { def client = ClientUser.get(session.clientUserID) client.email = params.email if(clientUserService.checkPassword(session.clientUserID , params.password) ==false) { flash.message = "Incorrect Password" client.discard() redirect(action:'changeEmail') } else if(!client.validate()) { flash.message = "Invalid Email Address" redirect(action:'changeEmail') } else { client.save(); session.clientUserID = null; flash.message = "Your email address has been changed, please login again" redirect(controller: 'clientLogin' , action:'index') } } Now what I noticed that was odd was that if I entered an invalid email then it would not save the changes (as expected) BUT if I entered the wrong password and a valid email then it would save the changes and even write them back into the database even though it would give the correct "invalid password" error message. I was puzzled so set break points in all the if/else if/else blocks and found that it was hitting the first if statement as expected and not hitting the others , so it would never come accross a call to the save() method, yet it was saved anyway. After a little research I came accross documentation for the discard() method which you can see used in the code above. So I added this but still no avail. I even tried using discard then reloading the client object from the DB again but still no dice. This is very frustrating and I would be grateful for any help, since I think that this should surely not be a complicated requirement!

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  • readObject() vs. readResolve() to restore transient fields

    - by Joonas Pulakka
    According to Serializable javadoc, readResolve() is intended for replacing an object read from the stream. But is it OK to use it for restoring transient fields, like so: private Object readResolve() { transientField = something; return this; } as opposed to using readObject(): private void readObject(ObjectInputStream s) { s.defaultReadObject(); transientField = something; } Is there any reason to choose one over other, when used to just restore transient fields?

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  • Reading Ontology with Jena, feeding it with RDF triples, and producing correct RDF string output.

    - by JonB
    Hi, I have an ontology, which I read in with Jena to help me scrape some RDFa triples from a website. I don't currently store these triples in a Jena model, but that is fairly straight forward to do, its on my to do next list. The area I am struggling with, though, is to get Jena to output correct RDF for the ontology I have. The ontology uses Owl and RDFS definitions, but when I pass some example triples into the model, they don't appear correctly. Almost as if it doesn't know anything about the ontology. The output is, however, still valid RDF, just it's not coming out in the form I was hoping for. Am I correct in thinking that Jena should be able to produce well written RDF (not just valid) about the triples I have collected, based on the ontology or does this out stretch what it is capable of? Many thanks for any input.

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  • dynamic behavior of factory class

    - by manu1001
    I have a factory class that serves out a bunch of properties. Now, the properties might come either from a database or from a properties file. This is what I've come up with. public class Factory { private static final INSTANCE = new Factory(source); private Factory(DbSource source) { // read from db, save properties } private Factory(FileSource source) { // read from file, save properties } // getInstance() and getProperties() here } What's a clean way of switching between these behaviors based on the environment. I want to avoid having to recompile the class each time.

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  • Getting the instance when Constructor#newInstance throws?

    - by Shtééf
    I'm working on a simple plugin system, where third party plugins implement a Plugin interface. A directory of JARs is scanned, and the implementing classes are instantiated with Constructor#newInstance. The thing is, these plugins call back into register* methods of the plugin host. These registrations use the Plugin instance as a handle. My problem is how to clean up these registrations if the constructor decides to fail and throw halfway through. InvocationTargetException doesn't seem to have anything on it to get the instance. Is there a way to get at the instance of an exception throwing constructor? P.S.: It's typically strongly advised to users that the constructor not do anything, but in practice people are doing it any ways.

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  • How to add two label in one gridbox?

    - by Jessy
    Hello everyone, How can I add two label in the same grid box? e.g. in row 1, col 1 the will be 2 labels? The code below will add the label in two different grid. JPanel chckBox = new JPanel(new GridLayout(1,8,3,3)); JLabel label1 = new JLabel("A"); JLabel label2 = new JLabel("B"); ... chckBox.add(label1); chckBox.add(label2); ...

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  • Pageview implementation

    - by The Elite Gentleman
    Hi everyone I want to add a pageview feature on my current web application. This page view is based on the count of user viewing the page. It must be unique, i.e. I must not view a person's page 10000 times and record it as 10000 views, just record 1 view instead. My question is, should I base my pageview count on IP address? If not, what is/are the best approach in doing this? I know that if the person has logged in to my system, I can simply use the user id stored in the session and check on the record if the user has/hasn't viewed the page and update accordingly. But for "anonymous" viewers, what is the best approach? Thanks. PS How does Youtube does it?

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  • What tool/framework to use for technical documentation?

    - by Pangea
    We develop products and frameworks to be used with in our organization. I am looking for programmer friendly documentation tools. I have researched on few options sometime back but couldn't decide which one to use. I am looking for suggestions from the people who already used these tools. docbook: springframework and hibernate use this format and this looks good. but I believe they have customized the default xslt/stylesheet. Can I copy and use their xslt and css (ofcourse with colors and images changed). Can I integrate the doc generation using maven? wiki: this is not friendly to the technical document writers and the documentation doesn't look professional. versioning is also not possible I believe word docs: this is what we use currently but it is hard to link and reuse common documents. DITA?

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  • Using SiteMesh with RequestDispatcher's forward()

    - by Rob Hruska
    I'm attempting to integrate SiteMesh into a legacy application using Tomcat 5 as my a container. I have a main.jsp that I'm decorating with a simple decorator. In decorators.xml, I've just got one decorator defined: <decorators defaultdir="/decorators"> <decorator name="layout-main" page="layout-main.jsp"> <pattern>/jsp/main.jsp</pattern> </decorator> </decorators> This decorator works if I manually go to http://example.com/my-webapp/jsp/main.jsp. However, there are a few places where a servlet, instead of doing a redirect to a jsp, does a forward: getServletContext().getRequestDispatcher("/jsp/main.jsp").forward(request, response); This means that the URL remains at something like http://example.com/my-webapp/servlet/MyServlet instead of the jsp file and is therefore not being decorated, I presume since it doesn't match the pattern in decorators.xml. I can't do a <pattern>/*</pattern> because there are other jsps that do not need to be decorated by layout-main.jsp. I can't do a <pattern>/servlet/MyServlet*</pattern> because MyServlet may forward to main.jsp sometimes and perhaps error.jsp at other times. Is there a way to work around this without expansive changes to how the servlets work? Since it's a legacy app I don't have as much freedom to change things, so I'm hoping for something configuration-wise that will fix this. SiteMesh's documentation really isn't that great. I've been working mostly off the example application that comes with the distribution. I really like SiteMesh, and am hoping I can get it to work in this case.

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  • Using thread inter-communication to increase my server app's IO throughput; not sure how

    - by Howard Guo
    My server application creates a new thread for each incoming connection. Incoming requests are serialized in a BlockingQueue. There is one worker thread taking items from the queue, produce a response and send the response through socket. I have noticed a throughput issue: Currently, worker thread is responsible of sending the response message through socket, thus severely wasting processing power and throughput. I am considering: rather than sending the response itself, why not telling network IO threads to send the response? However, when I think about thread inter-communication, I cannot yet figure out how to approach it: Worker thread will produce a response, but how will it inform the response message to IO thread? Is there a standard/best practice? Thank you.

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  • Can I close and reopen a socket?

    - by Roman
    I learned an example of usage of sockets. In this example a client sends a request to a server to open a socket and then the server (listening to a specific port) opens a socket and everything is fine, socket is "opened" from both sides (client and server). But it is still not clear to me how flexible is this stuff. For example, is it possible for the client to close an opened (from both ends) socket and to reopen it again (under condition that the server keeps the socket opened). Is it possible for the server to "know" that a socket was closed on the client side? Is it possible for the client to know that a socket was closed on the server side?

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  • get string from outside run programm

    - by Alex Berd
    Hello I have jsp page with text field and button. Also i have jar of another project. When i click on the button the MAIN.class of the jar is called and program is running in independent window(JFrame). After user is finished with the program and exits, I need to get the String of program that is generated on exit and paste it into the textbox (The String is HTML code) Is anyone else having this problem and has a solution? Thanks Alex

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