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  • To "null" or not to "null" my class's attributes

    - by Helper Method
    When I write a class in Java, I like to initialize the attributes which are set to a default value directly and attributes which are set by the caller in the constructor, something like this: public class Stack<E> { private List<E> list; private size = 0; public Stack(int initialCapacity) { list = new ArrayList<E>(initialCapacity); } // remainder omitted } Now suppose I have a Tree class: public class Tree<E> { private Node<E> root = null; // no constructor needed, remainder omitted } Shall I set the root attribute to null, to mark that it is set to null by default, or omit the null value?

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  • Retrieve a static variable using its name dynamically using reflection

    - by user2538438
    How to retrieve a static variable using its name dynamically using Java reflection? If I have class containing some variables: public class myClass { string [][] cfg1= {{"01"},{"02"},{"81"},{"82"}}; string [][]cfg2= {{"c01"},{"c02"},{"c81"},{"c82"}}; string [][] cfg3= {{"d01"},{"d02"},{"d81"}{"d82"}}; int cfg11 = 5; int cfg22 = 10; int cfg33 = 15; } And in another class I want variable name is input from user: class test { Scanner in = new Scanner(System.in); String userInput = in.nextLine(); // get variable from class myClass that has the same name as userInput System.out.println("variable name " + // correct variable from class) } Using reflection. Any help please?

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  • Generating Ant build file for a project in eclipse

    - by Negai
    Hi everyone. I have a project written in Java using eclipse and I would like to generate an Ant build file for it. How can it be done? I constantly need to keep it synchronized with the source code, so that I could promote it along with the code to the common repository when with the project structure is modified. I'm sorry for a stupid question like this. I've browsed across the forums, but still no luck. Thanks in advance.

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  • How to change the image by click keyboard arrows?

    - by Nitz
    Hey Guys, I have made one project in java. Now in this particular module, i am showing the user , so i am showing them a stock inventory. Now for doing this. As you will see in the screen shot [ i have put screenshot so you can understand well ]. To show the images , i have made one table and i have put labels in that and then i am setting the icon at the label. Now as soon as user click on the any image, then that image i put on big label. But this works perfect on mouse click but client want that , if user navigate the by keyboard arrow keys then in same should be happen. Means : User navigate by key board then it should reflect on that table [user should know that which is currently seleted ] and then as soon as the user navigate by key board arrow events and then click enter then that image should reflect on big label. Here is the Link for that screenshot.

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  • How can I leverage String constants in an XML file?

    - by jayshao
    I'd like to enforce standardized keys by storing them as static final String variables on a Java class, and either referencing or statically importing them, to use them as values in either XML, Strings, Methods, Annotations, etc. Does anyone know a good way to have Maven insert (like filtering) values like StringKeys.SOME_KEY into an XML file? e.g. something like <element value="${StringKeys.SOME_KEY}"/> or similar - the main idea is to enforce commonality and prevent key mis-alignment. Or an alternative solution to accomplish the same - with some semantic that if a non-existant String is referenced, that it fails during build? Bonus points if it works in C# as well.

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  • Should I use threeten instead of joda-time

    - by Yan Cheng CHEOK
    Hello all, I came across http://www.jroller.com/scolebourne/entry/why_jsr_310_isn_t. 1) I am currently migrating Java Calendar to joda-time. I was wondering, should I use threeten instead of joda-time? Is threeten production ready? 2) Can threeten library and joda-time libraries exist together in a same application? As I am using some 3rd parties libraries, which is using joda-time library too. 3) Will joda-time become an abandon project since there is threeten? Thanks.

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  • Multimap Space Issue: Guava

    - by Arpssss
    In my Java code, I am using Guavas Multimap (com.google.common.collect.Multimap) by using this: Multimap< Integer, Integer Index = HashMultimap.create() Here, Multimap key is some portion of URL and value is another portion of URL (converted into integer). Now, I assign my JVM 2560 Mb (2.5 GB) heap space (by using Xmx and Xms). However, it can only store 9 millions of such (key,value) pairs of integers (approx 10 million). But, theoretically (according to memory occupied by int) it should store more. Can anybody help me, 1) Why is this happening (means Multimap is taking lots of space) ? I checked my code with out inserting pairs in Multimap, it takes only 1/2 MB space. 2) Is there any other way or home-baked solution to solve this space issue ? More clearly, how to solve this memory issue ? Thanks in advance and any idea is perfectly OK for me.

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  • filter log file by defining regexes

    - by fmpdmb
    I have some HUGE log files (50Mb; ~500K lines) I need to start filtering some of the crap out of. The log files are being produced using log4j and have the basic pattern of: [log-level] date-time class etc, etc log-message I'm looking for a way that I can identify a regex start and regex end (or something similar) that will filter out the matching entries from the file so I can more easily wade through these massive files. I'm sure I could write a java program to accomplish this task, but I thought I'd ask the community before going down that path. Thanks in advance.

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  • Stopping the manipulation of variables used for data collection?

    - by Ruinous
    I am working on a project in java and I was hoping to be able to collect statistics from the client and a possible problem that I fear will occur is the manipulation of the variables used for collection which will lead to illegitimate statistics. Is it in any way possible to prevent the manipulation of variables or is it always possible? For example: I want to log the actions made per hour from the client. The variable acting as a counter for the amount of actions performed is manipulated and a much larger amount is added to the counter. This data is then uploaded to the server (Of course using a multi-tier architecture to prevent even more possible problems) and considered 'legit.' Is there any way to prevent this?

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  • Live output from .jar executed by PHP

    - by user2926097
    I have a php-script which executes a .jar-file: <?php passthru("java -jar nlp-server.jar 9000"); ?> I want to display the output generated by this .jar-file on a website. The problematic part is the fact that the .jar-file doesnt finish executing because its a server-application. Thus navigating to the php-file wont help and I didnt manage to make AJAX work either. Is there a way to display the "live" output of the .jar-file on a website?

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  • Ideally How many connections I have to open ?

    - by ranjith-kumar-u
    Hi All, Recently I attended interview in java, the interviewer asked a question like below: I have a request which go throgh A,B,C modules and response go back throgh A , in module A I need to talk to database and again in module C I need to talk to database, so in this situation how many connections you will open and where do you close those connections? My Answer: I said that in module A I will open a connection and I will close it then and there, then control go to module B then module C, in module C again I will open one more connection and i will close it again. then he asked me again another question I want to open one connection per one request processing, how can i do this?

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  • Parsing String to TreeNode

    - by Krusu70
    Anyone have a good algorithm how to parse a String to TreeNode in Java? Let's say we have a string s which says how to build a TreeNode. A(B,C) means that A is the name (String) of TreeNode, B is child of A (Treenode), C is sibling of A (TreeNode). So if I call function with string A(B(D,E(F,G)),C) (just a example), then I get a TreeNode equals to: level A (String: name), B - Child (TreeNode), C - Sibling (TreeNode) level B (String: name), D - Child of B (TreeNode), E - Sibling of B (TreeNode) level E (String: name), F - Child of E (TreeNode), G - Sibling of E (TreeNode) The name may not be 1 letter, it could be like real name (many letters).

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  • Definition of variables/fields type within a constructor, how is it done?

    - by elementz
    I just had a look at Suns Java tutorial, and found something that totally confused me: Given the following example: public Bicycle(int startCadence, int startSpeed, int startGear) { gear = startGear; cadence = startCadence; speed = startSpeed; } Why is it, that the types of the variables (fields?) gear, cadence and speed do not need to be defined? I would have written it as follows: public Bicycle(int startCadence, int startSpeed, int startGear) { int gear = startGear; int cadence = startCadence; int speed = startSpeed; } What would be the actual differnce?

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  • Tomcat servlet-api.jar problem

    - by CitadelCSCadet
    I am running a web application using Tomcat and Java Servlets, JSP's, etc. I am aware that in order to use Servlets, it is dependent on the Servlet-api.jar file. Initially I placed this jar file in the WEB-INF/lib/ directory. This has worked fine for me for months during the developmental phase. When we put the application onto the server space we are using, we started seeing wierd problems showing up in the Catalina.out file telling us that there was dependency problems with the servlet-api.jar file. I am aware that tomcat has this jar file in its container, and that I should remove it from the WEB-INF/lib/ directory. I have tried this and it does not work. What do I have to do when I remove this jar file from the local files and allow it to depend on tomcats servlet-api.jar file.

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  • Forward web request for directory index ('/') to an index.htm page in JBoss 4.0.5

    - by The Pretender
    I am using JBoss 4.0.5.GA to run a set of java applications. One of them is a web frontend, using Spring 1.4. URL mappings are configured in a way that 'fake' pages from request URLs are mapped to controllers. That means that when someone requests /index.htm, there's no actual 'index.htm' on disk, and that request maps to a specific conroller which then renders a jsp view. So the problem is as follows: I need to tell JBoss to somehow forward all requests for directory indices to corresponding 'index.htm' URLs like so: / ? /index.htm; /news/ ? /news/index.htm; /foo/bar/baz/ ? /foo/bar/baz/index.htm and so on. I can't use Tomcat's welcome-file-list feature because it looks for those files on disk, while all 'index.htm's are fake and don't actually exist on disk.

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  • Basic Hibernate question using and sql query

    - by Aerosteak
    Hello Sorry if this is basic but I cannot find the solution anywhere. I have an java Object ‘Person’ with 3 properties firstname,lastname and username. I have an Oracle Store procedure returning a Resultset with the 3 column. All works fine for that. Now I have another StoreProcedure that will only return firstname and lastname but not username. I get the following error : « could not read column value from result set username. » Hibernate tries to fetch the username property from the resultset. If I remove the property username, then it works. Do I have to Create a Special Pojo for Each type of resultset or can I tell Hibernate what to map for each result set? Please help.

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  • Some issue with bufferedReader

    - by thetna
    I have a java function as follows: public HashMap<String, ArrayList<Double>> embedWords(BufferedReader buffR1 { ArrayList<String > arrayList = new ArrayList<String>(); arrayList = getWords(buffR1); System.out.println("Word size:"+ arrayList.size()); ArrayList<ArrayList<Double>> arrList = getWordFeature(buffR1); System.out.println("Size of arrList:embedWords:"+arrList.size()); } Here , the problem is , the both of the function getWords and getWordFeatures can't give the size value. When i comment function getWords the function getWordFeature returns non-zero value .But when uncommented , the output is as follows: Word size:15055 Size of arrList:embedWords: 0

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  • Is it a good idea to use only a key to encrypt an entire (small) filesystem?

    - by Fernando Miguélez
    This question comes as part of my doubts presented on a broader question about ideas implementing a small encrypted filesystem on Java Mobile phones (J2ME, BlackBerry, Android). Provided the litte feedback received, considering the density of the question, I decided to divide those doubts into small questions. So to sum up I plan to "create" an encrypted filesystem for for mobile phones (with the help of BoucyCastle or a subset of JCE), providing an API that let access to them in a transparent way. Encryption would be carried out on a file basis (not blocks). My question is this: Is it a good idea to use only a simmetric key (maybe AES-256) to encrypt all the files (they wouldn't be that many, maybe tens of them) and store this key in a keystore (protected by a pin) or would you rather encrypt each file with an on-the-fly generated key stored alongside each file, encrypting that key with the "master" key stored on the keystore? What are the benefits/drawbacks of each approach?

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  • creating BeanInfo objects in NetBeans 6.1 does not work for some objects

    - by Coder
    I have recently learned about BeanInfo classes in Java, and have successfully used them to add icons to my custom GUI components which extend swing components such as JTextField, however i have a more specialized GUI component which extends from another one of my GUI components, which then extends from JTextField. Ie. the class hierarchy is of the form "A - B - JTextField". I can create a bean info object that works for class B, but when i click on the bean info editor option in netbeans to create a bean info object for class A, nothing happens. Ie. there is no error pop-up and a bean info object is not created. There isn't much difference between class A and B. Both A and B have default no argument constructors and they are very similar to each other. The only thing i can really think of is that A uses generics and B does not. I would like to create a beaninfo object for class A so that i can add custom icons for that component. Any help would be appreciated. Thanks.

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  • When to stop following the advice of static code analysis?

    - by bananeweizen
    I do use static code analysis on a project with more than 100.000 lines of Java code for quite a while now. I started with Findbugs, which gave me around 1500 issues at the beginning. I fixed the most severe over time and started using additional tools like PMD, Lint4J, JNorm and now Enerjy. With the more severe issues being fixed, there is a huge number of low severity issues. How do you handle these low priority issues? Do you try fixing all of them? Or only in newly written code? Do you regularly disable certain rules? (I found that I do on nearly any of the available tools). And if you ignore or disable rules, do you document those? What do your managers say about "leaving some thousand low priority issues not fixed"? Do you use (multiple) tool specific comments in the code or is there any better way?

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  • Getting object coordinates from camera

    - by user566757
    I've implemented a camera in Java using a position vector and three direction vectors so I can use gluLookAt(); moving around in `ghost mode' works fine enough, but I want to add collision detection. I can't seem to figure out how to transform my position vector to coordinates in which OpenGL draws my objects. A rough sketch of my drawing loop is this: glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glLoadIdentity(); camera.setView(); drawer.drawTheScene(); I'm at a loss of how to proceed; looking at the ModelView matrix between calls and my position vector, I haven't found any kind of correlation.

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  • Is concatenating with an empty string to do a string conversion really that bad?

    - by polygenelubricants
    Let's say I have two char variables, and later on I want to concatenate them into a string. This is how I would do it: char c1, c2; // ... String s = "" + c1 + c2; I've seen people who say that the "" + "trick" is "ugly", etc, and that you should use String.valueOf or Character.toString instead. I prefer this construct because: I prefer using language feature instead of API call if possible In general, isn't the language usually more stable than the API? If language feature only hides API call, then even stronger reason to prefer it! More abstract! Hiding is good! I like that the c1 and c2 are visually on the same level String.valueOf(c1) + c2 suggests something is special about c1 It's shorter. Is there really a good argument why String.valueOf or Character.toString is preferrable to "" +? Trivia: in java.lang.AssertionError, the following line appears 7 times, each with a different type: this("" + detailMessage);

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  • Hibernate and Child Objects (add versus clear)

    - by tyndall
    Lets say I have domain model with Automobile and Wheels. Wheels is a List of Wheels Wheels has a many-to-one relationship to Automobile. If I get an object back from Hibernate and it has 4 wheels. I take that object remove the 4 wheels and add 4. And then Save. If I ask Hibernate for the object again and it returns an auto with 8 wheels... what are we doing wrong? I don't have access to the source for a few days but want to give our Java devs a push in the right direction. Thanks.

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  • Getting print data - Windows (Redmon)

    - by Anurag Ramdasan
    I am trying to develop an app to retrieve print data, edit its content and then print the data. I am using RedMon for that purpose. But all the tutorials I have seen online as of now relates to storing the data into a PDF using RedMon. I want to be able to configure RedMon on a windows platform such that it writes the entire print data(the data that is bound to appear on the printing paper) as it is into a .txt file or maybe provide directly as an input to the java app that I have made. I have been unsuccessful in finding a solution for this till now. Is this achievable?

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  • How to get the action from the HttpServlet request to dispatch to multiple pages

    - by JFB
    I am using the Page Controller pattern. How could I use the same controller for two different pages by detecting the request action and then dispatching according to the result? Here is my code: account.jsp <form name="input" action="<%=request.getContextPath() %>/edit" method="get"> <input type="submit" value="Modifier" /> </form> Account Servlet public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println("received HTTP GET"); String action = request.getParameter("action"); if (action == null) { // the account page dispatch(request, response, "/account"); } else if (action == "/edit") { // the popup edit page dispatch(request, response, "/edit"); } protected void dispatch(HttpServletRequest request, HttpServletResponse response, String page) throws javax.servlet.ServletException, java.io.IOException { RequestDispatcher dispatcher = getServletContext() .getRequestDispatcher(page); dispatcher.forward(request, response); } }

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