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  • Generics in return types of static methods and inheritance

    - by Axel
    Generics in return types of static methods do not seem to get along well with inheritance. Please take a look at the following code: class ClassInfo<C> { public ClassInfo(Class<C> clazz) { this(clazz,null); } public ClassInfo(Class<C> clazz, ClassInfo<? super C> superClassInfo) { } } class A { public static ClassInfo<A> getClassInfo() { return new ClassInfo<A>(A.class); } } class B extends A { // Error: The return type is incompatible with A.getClassInfo() public static ClassInfo<B> getClassInfo() { return new ClassInfo<B>(B.class, A.getClassInfo()); } } I tried to circumvent this by changing the return type for A.getClassInfo(), and now the error pops up at another location: class ClassInfo<C> { public ClassInfo(Class<C> clazz) { this(clazz,null); } public ClassInfo(Class<C> clazz, ClassInfo<? super C> superClassInfo) { } } class A { public static ClassInfo<? extends A> getClassInfo() { return new ClassInfo<A>(A.class); } } class B extends A { public static ClassInfo<? extends B> getClassInfo() { // Error: The constructor ClassInfo<B>(Class<B>, ClassInfo<capture#1-of ? extends A>) is undefined return new ClassInfo<B>(B.class, A.getClassInfo()); } } What is the reason for this strict checking on static methods? And how can I get along? Changing the method name seems awkward.

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  • can't understand the url function used in the google taskque api documentation

    - by Bunny Rabbit
    import com.google.appengine.api.labs.taskqueue.Queue; import com.google.appengine.api.labs.taskqueue.QueueFactory; import static com.google.appengine.api.labs.taskqueue.TaskOptions.Builder.*; // ... Queue queue = QueueFactory.getDefaultQueue(); queue.add(url("/worker").param("key", key)) in the code example given on the google task queue documentation page i can't understand the url("/worker") function they are calling in the queues.add() invocation .

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  • Two collections manyToOne to same primary key

    - by Ethiel
    Hi, guys, I'm coding a web page in Hibernate-JPA and Oracle. I need the following: I have two classes: Place and Home. I need two collections of type Place in every Home: I do the following: Home: @ManyToOne @JoinColumn(name="ID_PLACES") private List<Places>places1; @ManyToOne @JoinColumn(name="ID_PLACES") private List<Places>Places2; However, hibernate got an exception (repeated column) and forces to me to mapping with insert and update to false. How Can I get Two ManyToOne relationship to same primary key with insert a true?.

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  • Generate URL for File

    - by Don
    The default output of File.toURL() is file:/c:/foo/bar These don't appear to work on windows, and need to be changed to file:///c:/foo/bar Does the format file:/c:/foo/bar work correctly on Unix (I don't have a Unix machine to test on)? Is there a library that can take care of generating a URL from a File that is in the correct format for the current environment?

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  • Mapping enum to a table with hibernate annotation

    - by Thierry-Dimitri Roy
    I have a table DEAL and a table DEAL_TYPE. I would like to map this code: public class Deal { DealType type; } public enum DealType { BASE("Base"), EXTRA("Extra"); } The problem is that the data already exist in the database. And I'm having a hard time mapping the classes to the database. The database looks something like that: TABLE DEAL { Long id; Long typeId; } TABLE DEAL_TYPE { Long id; String text; } I know I could use a simple @OneToMany relationship from deal to deal type, but I would prefer to use an enum. Is this possible? I almost got it working by using a EnumType.ORDINAL type. But unfortunately, my IDs in my deal type table are not sequential, and do not start at 1. Any suggestions?

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  • Create a new log file every time my program is run

    - by Bernhard V
    Hi, I am using the Apache commons logging library and log4j to generate my log files. Now I want to create a new file every time I run my program. The current count should be appended to the log file's name. For example: program_1.log program_2.log program_3.log Do you know how I could achieve this?

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  • Auto injecting logger with guice

    - by koss
    With reference to Guice's custom injections article, its TypeListener performs a check for InjectLogger.class annotation - which can be optional. Removing that check will inject to all Logger.class types. class Log4JTypeListener implements TypeListener { public <T> void hear(TypeLiteral<T> typeLiteral, TypeEncounter<T> typeEncounter) { for (Field field : typeLiteral.getRawType().getDeclaredFields()) { if (field.getType() == Logger.class && field.isAnnotationPresent(InjectLogger.class)) { typeEncounter.register(new Log4JMembersInjector<T>(field)); } } } } I'm tempted to remove "&& field.isAnnotationPresent(InjectLogger.class)" from the listener. If we're using Guice to inject all instances of our Logger, is there any reason not to do it automatically (without need to annotate)?

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  • Help need for openfast implementation

    - by ganuke
    Our stock exchange going to implement FAST messaging in their system in order to reduced the bandwidth usage. We have already implement the FIX based application to trade with Stock exchange. In future we need implement FIX FAST in our application to communicate with them. I found that OPEN FAST is FAST based library. But I do not have any idea how to start with it. I went through OpenFast web site but could not find much support on how to use templates and dictionaries. Can some one guide me or provide some resources to start with? Thanks in advance.

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  • Generating different randoms valid for a day on different independent devices?

    - by Pentium10
    Let me describe the system. There are several mobile devices, each independent from each other, and they are generating content for the same record id. I want to avoid generating the same content for the same record on different devices, for this I though I would use a random and make it so too cluster the content pool based on these randoms. Suppose you have choices from 1 to 100. Day 1 Device#1 will choose for the record#33 between 1-10 Device#2 will choose for the record#33 between 40-50 Device#3 will choose for the record#33 between 50-60 Device#1 will choose for the record#55 between 40-50 Device#2 will choose for the record#55 between 1-10 Device#3 will choose for the record#55 between 10-20 Device#1 will choose for the record#11 between 1-10 Device#2 will choose for the record#22 between 1-10 Device#3 will choose for the record#99 between 1-10 Day 2 Device#1 will choose for the record#33 between 90-100 Device#2 will choose for the record#33 between 1-10 Device#3 will choose for the record#33 between 50-60 They don't have access to a central server. Data available for each of them: IMEI (unique per mobile) Date of today (same on all devices) Record id (same on all devices) What do you think, how is it possible? ps. tags can be edited

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  • Why I cannot see an image if I do not use the full name of an image?

    - by Roman
    I try to add an image to JPanel. It works if I specify the full name of the image (including name of all folders). But I want my software to be machine independent (another machine does not have the same folder structure as my machine has). So, I put my image to the same place where the source is and in my code I use just name of the image (no folders' names). It does not work. I put my image into the folder where my executables are. It does not work again. So, why it does not work and what can I do with that?

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  • user enter data to different arrays

    - by user2900469
    This is fragment of my code (arrays as you can see): double[] Price; String[] names; int[] Quantity; Price = new double[5]; names = new String[5]; Quantity = new int[5]; Price[1] = 3.10; Price[2] = 7.80; Price[3] = 0.20; names[1] = "Ballpen"; names[2] = "Notebook"; names[3] = "Envelope"; Quantity[1] = 20; Quantity[2] = 5; Quantity[3] = 140; I enter data to arrays by myself in this case. Now i want to change my code so that my program asks user for names, price and quantity (using the Scanner class). After user enter data, program keep this in three different arrays. I dont know how to transfer data from user to arrays. I would be grateful for some example code or any help.

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  • How to trigger code on two different servers in a WAS cluster?

    - by Dean J
    I have an administrative page in a web application that resets the cache, but it only resets the cache on the current JVM. The web application is deployed as a cluster to two WAS servers. Any way that I can elegantly have the "clear cache" button on each server trigger the method on both JVMs? Edit: The original developer just wrote a singleton holding a HashMap to be the cache in question. Lightweight and (previously) worked just fine for the requirements. It caches content pulled from six or seven web services for specified amounts of time. Edit: The entire application in question is three pages, so the elegant solution might well be the lightest solution.

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  • Can fields of the class and arguments of the method interfere?

    - by Roman
    I have a class with a fields called "a". In the class I have a method and in the list of arguments of this method I also have "a". So, which "a" I will see inside of the method? Will it be the field or it will be the argument of the method? public class myClass { private String a; // Method which sets the value of the field "a". public void setA(String a) { a = a; } } By the way, there is a similar situation. A method has some local (for method) variables whose names coincide with the names of the fields. What will the "see" the method if I refer to such a method-local variable inside the method (the field or the local variable)?

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  • How to use Boolean variable in c:if

    - by Patriks
    I am using this code in jsf <c:if test="#{sV.done.booleanValue()}"> <option value="#{sV.id}" selected="selected">#{sV.text}</option> </c:if> <c:if test="#{not sV.done.booleanValue()}"> <option value="#{sV.id}">#{sV.text}</option> </c:if> sv is my class containing data (pojo), done is an Boolean variable, I want to display option tag with selected attribute if sV.done is true. But I couldn't make it. Don't know where I am wrong. Otherwise there can be something worong with c? because c:forEach was not working before some time in my case in same page. it can be the reason? Where I am wrong?

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  • How to test unescaped &nbsps; as a whitespace

    - by gleery
    I use apache common lang to unescape a block of html text which contains &nbsp;, I want to filter out blocks that contains only whitespaces. But I can't test the   as a whitespace. It's not in the normal whitespace list(http://en.wikipedia.org/wiki/Whitespace_character), and I try to print its Hex form by calling Character.getNumericValue which return -1. &nbsp should be a whitespace,isn't? But How can I test it?

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  • Detect main class

    - by Daniel
    Hoe can I detect the main class of my application? The one, which is either given on the command line or loaded from the jar given at the command line? If this is not possible, why not?

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  • Is it a good idea to close and open hibernate sessions frequently?

    - by Gaurav
    Hi, I'm developing an application which requires that state of entities be read from a database at frequent intervals or triggers. However, once hibernate reads the state, it doesn't re-read it unless I explicitly close the session and read the entity in a new session. Is it a good idea to open a session everytime I want to read the entity and then close it afterwards? How much of an overhead does this put on the application and the database (we use a c3p0 connection pool also)? Will it be enough to simply evict the entity from the session before reading it again?

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  • Compare class objects

    - by reto
    I have to compare a class object against a list of pre defined classes. Is it safe to use == or should I use equals()? if (klass == KlassA.class) { } else if (klass == KlassB.class) { } else if (klass == KlassC.class) { } else { } Note: I cannot use instanceof, I don't have an object, I just have the class object. I (mis)use it like an enum in this situation! Thanks!

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  • How often should we write unit tests?

    - by Midnight Blue
    Hi, I am recently introduced to the test-driven approach to development by my mentor at work, and he encourages me to write an unit-test whenenver "it makes sense." I understand some benefits of having a throughout unit-test suite for both regression testing and refractoring, but I do wonder how often and how throughout we should write unit-test. My mentor/development lead asks me to write a new unit test-case for a newly written control flow in a method that is already being tested by the exsisting test class, and I think it is an overkill. How often do you write your unit tests, and how detailed do you think your unit tests should be? Thanks!

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