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• Is using the break statement bad practice?

  - by Lchi

  I've been told by professors and peers at my university that using the break statement is bad practice, but through my coursework haven't come up with a great reason why. Those who claim that it is bad say that it's a "get out of jail free card" and that you can always avoid using it. My guesses for why its considered bad would be that you could possibly skip some cleanup code after the break, or similarly exit some control structure in an inconsistent state. Is there any reason why using break is(n't) bad practice?

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• Is it valid for Hibernate list() to return duplicates?

  - by skaffman

  Is anyone aware of the validity of Hibernate's Criteria.list() and Query.list() methods returning multiple occurrences of the same entity? Occasionally I find when using the Criteria API, that changing the default fetch strategy in my class mapping definition (from "select" to "join") can sometimes affect how many references to the same entity can appear in the resulting output of list(), and I'm unsure whether to treat this as a bug or not. The javadoc does not define it, it simply says "The list of matched query results." (thanks guys). If this is expected and normal behaviour, then I can de-dup the list myself, that's not a problem, but if it's a bug, then I would prefer to avoid it, rather than de-dup the results and try to ignore it. Anyone got any experience of this?

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• How do I write to a file in eclipse?

  - by fastcodejava

  If I have handle to file how do I create a document and write to it? Right now, I am having to delete the file completely and recreate with new content as shown below : IFile file = getFile(); file.delete(); file.create(input, false, null);

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• jaxb entity print out as xml

  - by Cristian Boariu

  Hi, I have a class, let's say User adnotated with @XmlRootElement, with some properties (name, surname etc). I use this class for REST operations, as application/xml. The client will POST User class so i want to keep the values in the log. Is there any method in jax-ws to prints out this object as xml? For instance: log.info("Customers sent a USER"+user.whichMethod()); Customer sent a User <user> <name>cristi</name> <surname>kevin</surname> </user> Thanks.

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• Jpa subclass mapping

  - by Roy Chan

  I am making a POS like system. I wonder how to map subclass using JPA (this is for my DAO). Product class has product details and OrderProduct class has information about the Product and details about the order. @Entity @Table(name="products") public class Product implements Serializable{ @Id @Column(name="id") @GeneratedValue(strategy = GenerationType.AUTO public int getId(){ return id;} /** Other get/set methods */ } @Entity @Table(name="order_products") public class OrderProduct extends Product{ @Id @Column(name="id") @GeneratedValue(strategy = GenerationType.AUTO) public int getId(){ return id;} /** Other get/set methods */ } I got complain about duplicate @Id. But OrderProduct class really need another id than the product one. How should I map this? DB is something like this Table products id int name varchar(32) Table order_product id int quantity int productid int fk referencing product table Would @IdClass or @AttributeOverride help?

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• Properly removing an Integer from a List<Integer>

  - by Yuval A

  Here's a nice pitfall I just encountered. Consider a list of integers: List<Integer> list = new ArrayList<Integer>(); list.add(5); list.add(6); list.add(7); list.add(1); Any educated guess on what happens when you execute list.remove(1)? What about list.remove(new Integer(1))? This can cause some nasty bugs. What is the proper way to differentiate between remove(int index), which removes an element from given index and remove(Object o), which removes an element by reference, when dealing with lists of integers? The main point to consider here is the one @Nikita mentioned - exact parameter matching takes precedence over auto-boxing.

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• What can cause my code to run slower when the server JIT is activated?

  - by durandai

  I am doing some optimizations on an MPEG decoder. To ensure my optimizations aren't breaking anything I have a test suite that benchmarks the entire codebase (both optimized and original) as well as verifying that they both produce identical results (basically just feeding a couple of different streams through the decoder and crc32 the outputs). When using the "-server" option with the Sun 1.6.0_18, the test suite runs about 12% slower on the optimized version after warmup (in comparison to the default "-client" setting), while the original codebase gains a good boost running about twice as fast as in client mode. While at first this seemed to be simply a warmup issue to me, I added a loop to repeat the entire test suite multiple times. Then execution times become constant for each pass starting at the 3rd iteration of the test, still the optimized version stays 12% slower than in the client mode. I am also pretty sure its not a garbage collection issue, since the code involves absolutely no object allocations after startup. The code consists mainly of some bit manipulation operations (stream decoding) and lots of basic floating math (generating PCM audio). The only JDK classes involved are ByteArrayInputStream (feeds the stream to the test and excluding disk IO from the tests) and CRC32 (to verify the result). I also observed the same behaviour with Sun JDK 1.7.0_b98 (only that ist 15% instead of 12% there). Oh, and the tests were all done on the same machine (single core) with no other applications running (WinXP). While there is some inevitable variation on the measured execution times (using System.nanoTime btw), the variation between different test runs with the same settings never exceeded 2%, usually less than 1% (after warmup), so I conclude the effect is real and not purely induced by the measuring mechanism/machine. Are there any known coding patterns that perform worse on the server JIT? Failing that, what options are available to "peek" under the hood and observe what the JIT is doing there?

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• Deploying Multiple Environments in Spring-MVC

  - by jboyd

  Currently all web apps are deployed using seperate config files: <!-- <import bean.... production/> --> <import bean... development/> This has disadvantages, even if you only need to swap out one config file, that I'm sure everyone is familiar with (wondering what just deployed without searching through XML is one of them) I want to add Logging to my application that basically says 'RUNNING IN PRODUCTION MODE', with a description of the services deployed and what mode they are working in. RUNNING IN PRODUCTION MODE Client Service - Production Messaging Service - Local and so on... Is this possible in Spring using a conventional deployment (putting a war on a server)? What other things do people do to manage deployments and software configurations? If not, what other ways could you achieve something similar?

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• How can I make a family of singletons?

  - by Jay

  I want to create a set of classes that share a lot of common behavior. Of course in OOP when you think that you automatically think "abstract class with subclasses". But among the things I want these classes to do is to each have a static list of instances of the class. The list should function as sort of a singleton within the class. I mean each of the sub-classes has a singleton, not that they share one. "Singleton" to that subclass, not a true singleton. But if it's a static, how can I inherit it? Of course code like this won't work: public abstract A { static List<A> myList; public static List getList() { if (myList==null) myList=new ArrayList<A>(10); return myList; } public static A getSomethingFromList() { List listInstance=getList(); ... do stuff with list ... } public int getSomethingFromA() { ... regular code acting against current instance ... } } public class A1 extends A { ... } public class A2 extends A { ... } A1 somethingfromA1List=(A1) A1.getSomethingFromList(); A2 somethingfromA2List=(A2) A2.getSomethingFromList(); The contents of the list for each subclass would be different, but all the code to work on the lists would be the same. The problem with the above code is that I'd only have one list for all the subclasses, and I want one for each. Yes, I could replicate the code to declare the static list in each of the subclasses, but then I'd also have to replicate all the code that adds to the lists and searches the list, etc, which rather defeats the purpose of subclassing. Any ideas on how to do this without replicating code?

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• Hibernate: Querying objects by attributes of inherited classes

  - by MichaelD

  Hi all, I ran into a problem with Hibernate concerning queries on classes which use inheritance. Basically I've the following class hierarchy: @Entity @Table( name = "recording" ) class Recording { ClassA attributeSet; ... } @Entity @Inheritance( strategy = InheritanceType.JOINED ) @Table( name = "classA" ) public class ClassA { String Id; ... } @Entity @Table( name = "ClassB1" ) @PrimaryKeyJoinColumn( name = "Id" ) public class ClassB1 extends ClassA { private Double P1300; private Double P2000; } @Entity @Table( name = "ClassB2" ) @PrimaryKeyJoinColumn( name = "Id" ) public class ClassB2 extends ClassA { private Double P1300; private Double P3000; } The hierarchy is already given like this and I cannot change it easily. As you can see ClassB1 and ClassB2 inherit from ClassA. Both classes contain a set of attributes which sometimes even have the same names (but I can't move them to ClassA since there are possible more sub-classes which do not use them). The Recording class references one instance of one of this classes. Now my question: What I want to do is selecting all Recording objects in my database which refer to an instance of either ClassB1 or ClassB2 with e.g. the field P1300 == 15.5 (so this could be ClassB1 or ClassB2 instances since the P1300 attribute is declared in both classes). What I tried is something like this: Criteria criteria = session.createCriteria(Recording.class); criteria.add( Restrictions.eq( "attributeSet.P1300", new Double(15.5) ) ); criteria.list(); But since P1300 is not an attribute of ClassA hibernate throws an exception telling me: could not resolve property: P1300 of: ClassA How can I tell hibernate that it should search in all subclasses to find the attribute I want to filter? Thanks MichaelD

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• Entities equals(), hashCode() and toString(). How to correctly implement them?

  - by spike07

  I'm implementing equals(), hashCode() and toString() of my entities using all the available fields in the bean. I'm getting some Lazy init Exception on the frontend when I try to compare the equality or when I print the obj state. That's because some list in the entity can be lazy initialized. I'm wondering what's the correct way to for implementing equals() and toString() on an entity object.

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• Android Content Provider database leak issue

  - by MattC

  I am writing a content provider for this application and in my content provider I am opening a database connection, running a query and returning the cursor of results to the calling program. If I close this database connection in the provider, the cursor has no results. If I leave it open, I get "leak found" errors in my DDMS log. What am I missing here? What's the clean, proper way to return a cursor of database results?

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• translating specifications into query predicates

  - by Jeroen

  I'm trying to find a nice and elegant way to query database content based on DDD "specifications". In domain driven design, a specification is used to check if some object, also known as the candidate, is compliant to a (domain specific) requirement. For example, the specification 'IsTaskDone' goes like: class IsTaskDone extends Specification<Task> { boolean isSatisfiedBy(Task candidate) { return candidate.isDone(); } } The above specification can be used for many purposes, e.g. it can be used to validate if a task has been completed, or to filter all completed tasks from a collection. However, I want to re-use this, nice, domain related specification to query on the database. Of course, the easiest solution would be to retrieve all entities of our desired type from the database, and filter that list in-memory by looping and removing non-matching entities. But clearly that would not be optimal for performance, especially when the entity count in our db increases. Proposal So my idea is to create a 'ConversionManager' that translates my specification into a persistence technique specific criteria, think of the JPA predicate class. The services looks as follows: public interface JpaSpecificationConversionManager { <T> Predicate getPredicateFor(Specification<T> specification, Root<T> root, CriteriaQuery<?> cq, CriteriaBuilder cb); JpaSpecificationConversionManager registerConverter(JpaSpecificationConverter<?, ?> converter); } By using our manager, the users can register their own conversion logic, isolating the domain related specification from persistence specific logic. To minimize the configuration of our manager, I want to use annotations on my converter classes, allowing the manager to automatically register those converters. JPA repository implementations could then use my manager, via dependency injection, to offer a find by specification method. Providing a find by specification should drastically reduce the number of methods on our repository interface. In theory, this all sounds decent, but I feel like I'm missing something critical. What do you guys think of my proposal, does it comply to the DDD way of thinking? Or is there already a framework that does something identical to what I just described?

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• JSF: Avoid nested update calls

  - by dhroove

  I don't know if I am on right track or not still asking this question. I my JSF project I have this tree structure: <p:tree id="resourcesTree" value="#{someBean.root}" var="node" selectionMode="single" styleClass="no-border" selection="#{someBean.selectedNode}" dynamic="true"> <p:ajax listener="#{someBean.onNodeSelect}" update=":centerPanel :tableForm :tabForm" event="select" onstart="statusDialog.show();" oncomplete="statusDialog.hide();" /> <p:treeNode id="resourcesTreeNode" > <h:outputText value="#{node}" id="lblNode" /> </p:treeNode> </p:tree> I have to update this tree after I added something or delete something.. But whenever I update this still its nested update also call I mean to say it also call to update these components ":centerPanel :tableForm :tabForm"... This give me error that :tableForm not found in view because this forms load in my central panel and this tree is in my right panel.. So when I am doing some operation on tree is it not always that :tableForm is in my central panel.. (I mean design is something like this only) So now my question is that can I put some condition or there is any way so that I can specify when to update nested components also and when not.... In nut shell is there any way to update only :resoucesTree is such a way that nested updates are not called so that I can avoid error... Thanks in advance.

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• How to use LocalValueBean in jsp page.

  - by Himanshu

  I have set certain bean label and bean value in one of my dao class.. I have created a list of LocalValueBean objects and passed it as a list to jsp.. now here at jsp i need to print the label seperately and on hover to the label i need to show the value.. i need to exttract or to say get those values in jsp directly... i have also imported the org.apache.struts.util.LabelValueBean in my jsp but still its not working.. please let me know if you any ideas...

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• How do we achieve "substring-match" under O(n) time?

  - by Pacerier

  I have an assignment that requires reading a huge file of random inputs, for example: Adana Izmir Adnan Menderes Apt Addis Ababa Aden ADIYAMAN ALDAN Amman Marka Intl Airport Adak Island Adelaide Airport ANURADHAPURA Kodiak Apt DALLAS/ADDISON Ardabil ANDREWS AFB etc.. If I specify a search term, the program is supposed to find the lines whereby a substring occurs. For example, if the search term is "uradha", the program is supposed to show ANURADHAPURA. If the search term is "airport", the program is supposed to show Amman Marka Intl Airport, Adelaide Airport A quote from the assignment specs: "You are to program this application taking efficiency into account as though large amounts of data and processing is involved.." I could easily achieve this functionality using a loop but the performance would be O(n). I was thinking of using a trie but it seems to only work if the substring starts from index 0. I was wondering what solutions are there which gives a performance better than O(n)?

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• HibernateFilter.doFilter ServletException?

  - by Austin R

  I have pretty much zero experience setting up servers, but currently my job is to set one up (don't ask why). It's an an apache-tomcat6 server. I followed some instructions step by step, and when it came time to test that everything was working, here's what I got: I know this is a bit of a shot in the dark, but does anyone know what I can do to fix this? Please let me know if there's any further information I can provide to help!

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• Get enum by it's inner field

  - by zeroed

  Hi! Have enum with inner fields, kind of map. Now I need to get enum by it's inner field. Wrote this: package test; /** * Test enum to test enum =) */ public enum TestEnum { ONE(1), TWO(2), THREE(3); private int number; TestEnum(int number) { this.number = number; } public TestEnum findByKey(int i) { TestEnum[] testEnums = TestEnum.values(); for (TestEnum testEnum : testEnums) { if (testEnum.number == i) { return testEnum; } } return null; } } But it's not very efficient to look up through all enums each time I need to find appropriate instance. Is there any other way to do the same?

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• Are multiply-thrown Exceptions checked or runtime?

  - by froadie

  I have an Exception chain in which method1 throws an Exception to method2 which throws the Exception on to main. For some reason, the compiler forces me to deal with the error in method2 and marks it as an error if I don't, indicating that it's a checked Exception. But when the same Exception is thrown further down the line to main, the compiler allows me to ignore it and doesn't display any errors. The original Exception in method1 is a ParseException, which is checked. But the method has a generic throws Exception clause in the header, and the same object is thrown to method2, which has an identical throws Exception clause. When and how does this Exception lose the status of being checked / caught by the compiler? Edited to clarify: public void method1() throws Exception{ // code that may generate ParseException } public void method2() throws Exception{ method1(); //compiler error } public static void main(String[] args){ method2(); //ignored by compiler }

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• JTextField that has inner fields or preformated format, something like the ip field in windows

  - by dimitar

  Hello guys, i want to create a text field that will be for date and will have dd.mm.YYYY format. Now what i want to do is the user to type only the numbers, not the dots to. So the field would be like: _ _. _ _ . _ _ _ _ So when the user wants to type the date: 15.05.2010 for example, he will only type the numbers in the sequence 15052010. Also i would like, when he preses on left or right arrow, the cursor to go from one field(not JTextField, but field in the JTextField). So lets say i have JTextField with text in it: 15.05.2010, so if user is on the beginning and he preses right arrow, the cursor to go to the .05 field. I hope you understand me 'cos right now i don't any idea how to make this, or at least how to look for it on google. Thank you.

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• How to sort a key of a map

  - by Tsuna Sawada

  How to sort (any kind of sorting) a key of a map(treemap or hashmap) i have a problem and it goes like this. i have a map that has a key of 27527-683, 27525-1179, 27525-1571, 27525-1813, 27525-4911, 27526-1303, 27526-3641, 27525-3989, 27525-4083, 27525-4670, 27526-4102, 27526-558, 27527-2411, 27527-4342 this is the list of keys and the value for each of the key is a list. now, how can i sort this key in ascending order by number. ex. if i want to sort : 1,2,11,20,31,3,10 i want to have as output is : 1,2,3,10,11,20,31 but when i use the autosort of treemap the output goes : 1,10,11,2,20,3,31 how can i sort it in ascending order by numeric? please help me. i can't think of anymore ways because this is my first time handling map and list

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• Using Comparable to compare objects and sorting them in a TreeMap

  - by arjacsoh

  II cannot understand how should the natural ordering of class be "consistent with equals" when implementing the Comparable interface. I deteted a flaw in my program and therefore I deteced that in the documentantion of the interface Comparable. My problem is that although two Objects are considered as distinct on the base of equals method, the TreeMap structure treats them as equal and consequently does not accept the second insert. The sample code is: public class Car implements Comparable<Car> { int weight; String name; public Car(int w, String n) { weight=w; name=n; } public boolean equals(Object o){ if(o instanceof Car){ Car d = (Car)o; return ((d.name.equals(name)) && (d.weight==weight)); } return false; } public int hashCode(){ return weight/2 + 17; } public String toString(){ return "I am " +name+ " !!!"; } public int compareTo(Car d){ if(this.weight>d.weight) return 1; else if(this.weight<d.weight) return -1; else return 0; } /*public int compareTo(Car d){ return this.name.compareTo(d.name); }*/ } public static void main(String[] args) { Car d1 = new Car(100, "a"); Car d2 = new Car(110, "b"); Car d3 = new Car(110, "c"); Car d4 = new Car(100, "a"); Map<Car, Integer> m = new HashMap<Car, Integer>(); m.put(d1, 1); m.put(d2, 2); m.put(d3, 3); m.put(d4, 16); for(Map.Entry<Car, Integer> me : m.entrySet()) System.out.println(me.getKey().toString() + " " +me.getValue()); TreeMap<Car, Integer> tm = new TreeMap<Car, Integer>(m); System.out.println("After Sorting: "); for(Map.Entry<Car, Integer> me : tm.entrySet()) System.out.println(me.getKey().toString() + " " +me.getValue()); } The output is : I am a !!! 16 I am c !!! 3 I am b !!! 2 After Sorting: I am a !!! 16 I am c !!! 2 That is, that the object c has replaced (somewhat) object b. If I comment the original equals method and uncomment the second equals method, which compares the objects according name, the output is the expected: I am a !!! 16 I am c !!! 3 I am b !!! 2 After Sorting: I am a !!! 16 I am b !!! 2 I am c !!! 3 Why does it come around in this way and what should I alter in order to insert and sort different objects with some attributes of equal value in a TreeMap?

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• Children in Enumeration

  - by marionmaiden

  Hello I have a enumeration for elements in a JTree When I find some specific element in this JTree, I want to check it's children. Do the method children() in a Enumeration check it's grandcildren too? For example, let's supose this JTree, considering the identation as new levels of the tree: Fruits apple grape orange peach pineapple strawberry banana If I get the children of grape, will I have just orange and peach or will I get peach children (pineaple) too?

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• javascript server issue

  - by sarah

  Onchage of selection i am calling a javascript to make a server call using struts1.2 but its not making a call.Please let me know where i am going wrong,below is the code <html:form action="/populate"> <html:select property="tName" onchange="test()">"> <html:option value="">SELECT</html:option> <html:options name="tList" /> </html:select> </html:form> and stuts-config has <action path="/populate" name="tForm" type="com.testAction" validate="false" parameter="method" scope="request" > <forward name="success" path="/failure.jsp" /> </action> and javascript is function test(){ var selObj = document.getElementById("tName"); var selIndex = selObj.selectedIndex; if (selIndex != 0) { document.form[0].selIndex.action="/populate.do?method=execute&testing="+selIndex; document.form[0].submit(); } }

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• Add 'expand' button to JTree node that has no children?

  - by thedude19

  I'd like to add the 'expand' button to my JTree's nodes to indicate that they are expandable. The catch is that they have no children until the user clicks on them (due to processing that happens in the background). Is there any way I can set a node as a parent or having children without it actually having children? Thanks

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