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  • Comparable and Comparator contract with regards to null

    - by polygenelubricants
    Comparable contract specifies that e.compareTo(null) must throw NullPointerException. From the API: Note that null is not an instance of any class, and e.compareTo(null) should throw a NullPointerException even though e.equals(null) returns false. On the other hand, Comparator API mentions nothing about what needs to happen when comparing null. Consider the following attempt of a generic method that takes a Comparable, and return a Comparator for it that puts null as the minimum element. static <T extends Comparable<? super T>> Comparator<T> nullComparableComparator() { return new Comparator<T>() { @Override public int compare(T el1, T el2) { return el1 == null ? -1 : el2 == null ? +1 : el1.compareTo(el2); } }; } This allows us to do the following: List<Integer> numbers = new ArrayList<Integer>( Arrays.asList(3, 2, 1, null, null, 0) ); Comparator<Integer> numbersComp = nullComparableComparator(); Collections.sort(numbers, numbersComp); System.out.println(numbers); // "[null, null, 0, 1, 2, 3]" List<String> names = new ArrayList<String>( Arrays.asList("Bob", null, "Alice", "Carol") ); Comparator<String> namesComp = nullComparableComparator(); Collections.sort(names, namesComp); System.out.println(names); // "[null, Alice, Bob, Carol]" So the questions are: Is this an acceptable use of a Comparator, or is it violating an unwritten rule regarding comparing null and throwing NullPointerException? Is it ever a good idea to even have to sort a List containing null elements, or is that a sure sign of a design error?

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  • Object Slicing, Is it advantage ?

    - by harigm
    Object slicing is some thing that object looses some of its attributes or functions when a child class is assigned to base class. Some thing like Class A{ } Class B extends A{ } Class SomeClass{ A a = new A(); B b = new B(); // Some where if might happen like this */ a = b; (Object slicing happens) } Do we say Object slicing is any beneficial in any ways? If yes, can any one please tell me how object slicing be a helpful in development and where it might be helpful?

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  • Highlight field in source code pane of Findbugs UI

    - by Ryan Fernandes
    I'm using a class that extends BytecodeScanningDetector to check for some problematic fields in a class. After detecting whether the field is problematic, I add it to the bug report like below: Once I run findbugs, it identifies the bug, lists it in the left pane, but does not highlight the corresponding source line. Any hints/help on this will be very appreciated. public void visit(Field f) { if (isProblematic(getXField())) { bugReporter.reportBug(new BugInstance(this, tBugType, HIGH_PRIORITY) .addClass(currentClass) //from visit(JavaClass) .addField(this)); } } public void visit(JavaClass someObj) { currentClass = someObj.getClassName(); } P.S. I tried posting this on the findbugs list but... no joy.

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  • Restlet/Jackson works differently when object implements Serializable

    - by ravyoli
    I am sending an object with some primitive fields using Restlet with Jackson converter. Up until now it worked great. But then I needed my object to implement Serializable, because I need to store it in memcache of GAE. For some reason - when the class implements Serializable, things stop working. Restlet sends a different string representation from before, and I can't even print that string in the server. I tried printing its byte value, char-by-char and the first numbers are: 0xfffd 0xfffd 0x0000 0x0005 0x0073 0x0072 Thanks a lot!

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  • Obfuscating Struts2 web application ..

    - by Xinus
    I want to obfuscate J2EE application which uses Struts2 framework, I tried using Proguard but its changing package and class names which does not get reflected stuts.xml file, Is it impossible to obfuscate struts2 web application ? Or any other way ?

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  • Counter that will remember it's value

    - by owca
    I have a task to operate on complex number. Each number consists of double r = real part, double i = imaginary part and String name. Name must be set within constructor, so I've created int counter, then I'm sending it's value to setNextName function and get name letter back. Unfortunately incrementing this 'counter' value works only within costructor and then it is once again set to 0. How to deal with that?Some constant value? And second problem is that I also need to provide setNextNames(char c) function that will change the counter current value. The code : public class Imaginary { private double re; private double im; private String real; private String imaginary; private String name; private int counter=0; public Imaginary(double r, double u){ re = r; im = u; name = this.setNextName(counter); counter++; } public static String setNextName(int c){ String nameTab[] = {"A","B","C","D","E","F","G","H","I","J","K","L","M","N", "O","P","Q","R","S","T","U","W","V","X","Y","Z"}; String setName = nameTab[c]; System.out.println("c: "+c); return setName; } public static String setNextName(char c){ // //don't know how to deal with this part // }

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  • Using progress bar in file search

    - by i2ijeya
    I am writing an application which will search for a particular file or files from the respective path. During searching i need to deploy a progress bar which must run according to the search. so how i can do that? and if possible please post the code?

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  • Spring validation errors not displayed

    - by Art Vandelay
    I have the following situation. I have a validator to validate my command object and set the errors on a Errors object to be displayed in my form. The validator is invoked as expected and works okay, but the errors i set on the Errors objects are not displayed, when i am sent back to my form because of the validation errors. Validator: public void validate(Object obj, Errors err) { MyCommand myCommand = (MyCommand) obj; int index = 0; for (Field field : myCommand.getFields()) { if (field.isChecked()) { if ((field.getValue() == null) || (field.getValue().equals(""))) { err.rejectValue("fields[" + index + "].value", "errors.missing"); } } index++; } if (myCommand.getLimit() < 0) { err.rejectValue("limit", "errors.invalid"); } } Command: public class MyCommand { private List<Field> fields; private int limit; //getters and setters } public class Field { private boolean checked; private String name; private String value; //getters and setters } Form: <form:form id="myForm" method="POST" action="${url}" commandName="myCommand"> <c:forEach items="${myCommand.fields}" var="field" varStatus="status"> <form:checkbox path="fields[${status.index}].checked" value="${field.checked}" /> <c:out value="${field.name}" /> <form:input path="fields[${status.index}].value" /> <form:errors path="fields[${status.index}].value" cssClass="error" /></td> <form:hidden path="fields[${status.index}].name" /> </c:forEach> <fmt:message key="label.limit" /> <form:input path="limit" /> <form:errors path="limit" cssClass="error" /> </form:form> Controller: @RequestMapping(value = REQ_MAPPING, method = RequestMethod.POST) public String onSubmit(Model model, MyCommand myCommand, BindingResult result) { // validate myCommandValidator.validate(myCommand, result); if (result.hasErrors()) { model.addAttribute("myCommand", myCommand); return VIEW; } // form is okay, do stuff and redirect } Could it be that the paths i give in the validator and tag are not correct? The validator validates a command object containing a list of objects, so that's why i give a index on the list in the command object when registering an error message (for example: "fields["+index+"]".value). Or is it that the Errors object containing the errors is not available to my view? Any help is welcome and appreciated, it might give me a hint or point me in right direction.

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  • With the introduction of the HTML5 <canvas> element, could Swing be implemented in GWT?

    - by knorv
    With the introduction of the HTML5 <canvas> element, could Swing theoretically be implemented in Google Web Toolkit (GWT) by using the <canvas> tag for drawing? I'm aware of efforts to port source code from using Swing calls to GWT calls, but what I'm after is a pure behind the scenes port where a Swing application would compile under GWT without any source code modifications. Is that theoretically possible? Why? Why not?

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  • How to prevent "Local transaction already has 1 non-XA Resource" exception?

    - by Zeratul
    Hi, I'm using 2 PU in stateless EJB and each of them is invoked on one method: @PersistenceContext(unitName="PU") private EntityManager em; @PersistenceContext(unitName="PU2") private EntityManager em2; @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW ) public void getCandidates(final Integer eventId) throws ControllerException { ElectionEvent electionEvent = em.find(ElectionEvent.class, eventId); ... Person person = getPerson(candidate.getLogin()); ... } @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW ) private Person getPerson(String login) throws ControllerException { Person person = em2.find(Person.class, login); return person; } Those methods are annotated with REQUIRES_NEW transcaction to avoid this exception. When I was calling these method from javaFX applet, all worked as expected. Now I'm trying to call them from JAX-RS webservice (I don't see any logical difference as in both cases ejb was looked up in initial context) and I keep getting this exception. When I set up XADatasource in glassfish 2.1 connection pools, I got nullpointer exception on em2. Any ideas what to try next? Regards

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  • JPA - Performance with using multiple entity manager

    - by Nguyen Tuan Linh
    My situation is: The code is not mine I have two kinds of database: one is Dad, one is Son. In Dad, I have a table to store JNDI name. I will look up Dad using JNDI, create entity manager, and retrieve this table. From these retrieved JNDI names, I will create multiple entity managers using multiple Son databases. The problem is: Son have thousands of entities. It takes each Son database around 10 minutes to load all entities. If there is 4 Son databases, it will be 40 minutes. My question: Is there any way to load all entities and use them for all entity manager? Please look at the code below For each Son JNDI: Map<String, String> puSonProperties = new HashMap<String, String>(); puSonProperties.put("javax.persistence.jtaDataSource", sonJndi); EntityManagerFactory emf = Persistence.createEntityManagerFactory("PUSon", puSonProperties); PUSon - All of them use the same persistence unit log.info("Verify entity manager for son: {0} - {1}", sonCode, emSon.find(Son_configuration.class, 0) != null ? "ok" : "failed!"); This is the actual code where the loading of all entities begins. 10 mins.

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  • Adding an HTTP Header to the request in a servlet filter

    - by Mason
    I'm integrating with an existing servlet that pulls some properties out of the HTTP header. Basically, I'm implementing an interface that doesn't have access to the actual request, it just has access to a map of k-v for the HTTP headers. I need to pass in a request parameter. The plan is to use a servlet filter to go from parameter to header value but of course the HttpServletRequest object doesn't have an addHeader() method. Any ideas?

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  • How to avoid serializing zero values with Simple Xml

    - by Bram Vandenbussche
    I'm trying to serialise an object using simple xml (http://simple.sourceforge.net/). The object setup is pretty simple: @Root(name = "order_history") public class OrderHistory { @Element(name = "id", required = false) public int ID; @Element(name = "id_order_state") public int StateID; @Element(name = "id_order") public int OrderID; } The problem is when I create a new instance of this class without an ID: OrderHistory newhistory = new OrderHistory(); newhistory.OrderID = _orderid; newhistory.StateID = _stateid; and I serialize it via simple xml: StringWriter xml = new StringWriter(); Serializer serializer = new Persister(); serializer.write(newhistory, xml); it still reads 0 in the resulting xml: <?xml version='1.0' encoding='UTF-8'?> <order_history> <id>0</id> <id_order>2</id_order> <id_order_state>8</id_order_state> </order_history> I'm guessing the reason for this is that the ID property is not null, since integers can't be null. But I really need to get rid of this node, and I'd rather not remove it manually. Any clues anyone?

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  • how can I handle user defined exceptions and after handling them resume the flow of program. here is

    - by fari
    /** * An exception thrown when an illegal side pit was * specified (i.e. not in the range 1-6) for a move */ public class IllegalSidePitNumException extends RuntimeException { /** * Exception constructor. * @param sidePitNum the illegal side pit that was selected. */ public IllegalSidePitNumException(int sidePitNum) { super("No such side pit number: "+sidePitNum); } } how do i use this ina program and then resume for there. I do not want the program to end but want to handle the exception and continue.

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  • unable to start .bat file from JSP

    - by Stardust
    I have a batch file runthis.bat If I double click on this a text file is being created with name dir.txt Now I have to run this batch file using JSP. <% Runtime run =Runtime.getRuntime(); run.exec("C:/Program Files/Apache Software Foundation/Tomcat 5.5/webapps/try/runthis.bat"); out.println("SUCCESS"); %> I'm getting the output SUCCESS on a webpage but this batch file is not running. Whats might be the problem?

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  • Try all available WSDL IPs with JAX-WS

    - by Asaf
    I'm using JAX-WS to open a service port. When the DNS exposes two IPs for the DNS entry (of the WSDL), the Service tries to use only the first - resulting in a "Failed to access the WSDL at: http://some.url.com/someDocument?wsdl. It failed with: Connection refused: connect" exception. I've found an issue filed against JAX-WS, but with no resolution. this is the comment that describes my problem best. The code is just a one-liner: Service service = Service.create("http://some.url.com/someDocument?wsdl", engineQName); the smarts is exposing those two A records on http://some.url.com/ at the DNS. Can anyone help? 10x,

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  • JavaFX: Update of ListView if an element of ObservableList changes

    - by user1828169
    I would like to display a list of persons (coded in POJOS, and containing a name and surname property) using a JavaFX ListView control. I created the ListView and added the list of persons as an ObservableList. Everything works fine if I delete or add a new person to the ObservableList, but changes in the POJO do not trigger an update of the ListView. I have to remove and add the modified POJO from the ObservableList to trigger the update of the ListView. Is there any possibility to display changes in POJOS without the workaround described above?

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  • Get children count via HQL

    - by Thomas Lötzer
    Hi, I have a one-to-many mapping between a parent entity and child entities. Now I need to find the number of children associated with each parent for a list of parents. I am trying to do this with HQL but I am not sure how I can get the list of parents in there. Also, I don't know how I can return the entity itself and not just its ID. My current HQL query is: select new map(parent.id as parentId, count(*) as childCount) from Parent parent left join parent.children children group by parent.id but this only returns the ID and does not filter on specific parents. EDIT Based on Pascal's answer I have modified the query to select new map(parent as parent, count(elements(parent.children)) as childCount) from Parent parent group by parent That does work, but is prohibitively slow: 30 seconds instead of 400 ms on the same database.

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  • controlling threads flow

    - by owca
    I had a task to write simple game simulating two players picking up 1-3 matches one after another until the pile is gone. I managed to do it for computer choosing random value of matches but now I'd like to go further and allow humans to play the game. Here's what I already have : http://paste.pocoo.org/show/201761/ Class Player is a computer player, and PlayerMan should be human being. Problem is, that thread of PlayerMan should wait until proper value of matches is given but I cannot make it work this way. Logic is as follows: thread runs until matches equals to zero. If player number is correct at the moment function pickMatches() is called. After decreasing number of matches on table, thread should wait and another thread should be notified. I know I must use wait() and notify() but I can't place them right. Class Shared keeps the value of current player, and also amount of matches. public void suspendThread() { suspended = true; } public void resumeThread() { suspended = false; } @Override public void run(){ int matches=1; int which = 0; int tmp=0; Shared data = this.selectData(); String name = this.returnName(); int number = this.getNumber(); while(data.getMatches() != 0){ while(!suspended){ try{ which = data.getCurrent(); if(number == which){ matches = pickMatches(); tmp = data.getMatches() - matches; data.setMatches(tmp, number); if(data.getMatches() == 0){ System.out.println(" "+ name+" takes "+matches+" matches."); System.out.println("Winner is player: "+name); stop(); } System.out.println(" "+ name+" takes "+matches+" matches."); if(number != 0){ data.setCurrent(0); } else{ data.setCurrent(1); } } this.suspendThread(); notifyAll(); wait(); }catch(InterruptedException exc) {} } } } @Override synchronized public int pickMatches(){ Scanner scanner = new Scanner(System.in); int n = 0; Shared data = this.selectData(); System.out.println("Choose amount of matches (from 1 to 3): "); if(data.getMatches() == 1){ System.out.println("There's only 1 match left !"); while(n != 1){ n = scanner.nextInt(); } } else{ do{ n = scanner.nextInt(); } while(n <= 1 && n >= 3); } return n; } }

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  • Invert linear linked list

    - by ArtWorkAD
    Hi, a linear linked list is a set of nodes. This is how a node is defined (to keep it easy we do not distinguish between node an list): class Node{ Object data; Node link; public Node(Object pData, Node pLink){ this.data = pData; this.link = pLink; } public String toString(){ if(this.link != null){ return this.data.toString() + this.link.toString(); }else{ return this.data.toString() ; } } public void inc(){ this.data = new Integer((Integer)this.data + 1); } public void lappend(Node list){ Node child = this.link; while(child != null){ child = child.link; } child.link = list; } public Node copy(){ if(this.link != null){ return new Node(new Integer((Integer)this.data), this.link.copy()); }else{ return new Node(new Integer((Integer)this.data), null); } } public Node invert(){ Node child = this.link; while(child != null){ child = child.link; } child.link = this;.... } } I am able to make a deep copy of the list. Now I want to invert the list so that the first node is the last and the last the first. The inverted list has to be a deep copy. I started developing the invert function but I am not sure. Any Ideas? Update: Maybe there is a recursive way since the linear linked list is a recursive data structure. I would take the first element, iterate through the list until I get to a node that has no child and append the first element, I would repeat this for the second, third....

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  • Difference between null==object and object==null

    - by priyank.mp
    Hi I would like to know diff between the above comparisons? I am getting null pointer exception when I check object.getItems() == null. But if I change it to null == object.getItems(), it workes fine. I did look into this http://stackoverflow.com/questions/2938476/what-is-the-difference-between-null-object-and-objectnull-closed But I didnt get satisfactory answer.

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