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  • Reference variable to an object instantiated/initialized in another class in Java

    - by Alex
    The reason I'm asking is because I'm getting NullPointerException. I now this is very easy but I'm pretty new programming and find this a bit confusing. So say I have initialized an object in a class and want to access that same object from another class. Like now for instance I'm working on a small Chess game, in my model Game class I have an instance of Board, an object. Board, in turn, has an array of Squares. Square[][]. Game has board, board has Square[][]. Now if I want to access the Square[][] through the object board (in Game) of type Board. Do I just declare a variable with the same name and type or do I have to initialize it again? Board board OR Board board = new Board(); Note, I have already initialized board in the class Game so if I do it again, won't they be two totally different Board objects?

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  • Java application on windows server possibility?

    - by Shawn Mclean
    I'd like to know if it is possible to have this application (neo4j) running on windows server 2008 alongside an asp.net mvc application. Reason for this, I need to access the graph database (neo4j) which provides a RESTful service from my mvc application. How would I go about setting up this architecture?

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  • java template design

    - by Sean Nguyen
    Hi, I have this class: public class Converter { private Logger logger = Logger.getLogger(Converter.class); public String convert(String s){ if (s == null) throw new IllegalArgumentException("input can't be null"); logger.debug("Input = " + s); String r = s + "abc"; logger.debug("Output = " + s); return r; } public Integer convert(Integer s){ if (s == null) throw new IllegalArgumentException("input can't be null"); logger.debug("Input = " + s); Integer r = s + 10; logger.debug("Output = " + s); return r; } } The above 2 methods are very similar so I want to create a template to do the similar things and delegate the actual work to the approriate class. But I also want to easily extends this frame work without changing the template. So for example: public class ConverterTemplate { private Logger logger = Logger.getLogger(Converter.class); public Object convert(Object s){ if (s == null) throw new IllegalArgumentException("input can't be null"); logger.debug("Input = " + s); Object r = doConverter(); logger.debug("Output = " + s); return r; } protected abstract Object doConverter(Object arg); } public class MyConverter extends ConverterTemplate { protected String doConverter(String str) { String r = str + "abc"; return r; } protected Integer doConverter(Integer arg) { Integer r = arg + 10; return r; } } But that doesn't work. Can anybody suggest me a better way to do that? I want to achieve 2 goals: 1. A template that is extensible and does all the similar work for me. 2. I ant to minimize the number of extended class. Thanks,

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  • JAVA: XML parsers gives null element

    - by Johan
    When I try to parse a XML-file, it gives sometimes a null element by the title. I think it has to do with HTML-tags &#039; How can I solve this problem? I have the follow XML-file: <item> <title>&#039; Nieuwe DVD &#039;</title> <description>tekst, tekst tekst</description> <link>dvd.html</link> <category>nieuws</category> <pubDate>Sat, 1 Jan 2011 9:24:00 +0000</pubDate> </item> And the follow code to parse the xml-file: //DocumentBuilderFactory, DocumentBuilder are used for //xml parsing DocumentBuilderFactory dbf = DocumentBuilderFactory .newInstance(); DocumentBuilder db = dbf.newDocumentBuilder(); //using db (Document Builder) parse xml data and assign //it to Element Document document = db.parse(is); Element element = document.getDocumentElement(); //take rss nodes to NodeList element.normalize(); NodeList nodeList = element.getElementsByTagName("item"); if (nodeList.getLength() > 0) { for (int i = 0; i < nodeList.getLength(); i++) { //take each entry (corresponds to <item></item> tags in //xml data Element entry = (Element) nodeList.item(i); entry.normalize(); Element _titleE = (Element) entry.getElementsByTagName( "title").item(0); Element _categoryE = (Element) entry .getElementsByTagName("category").item(0); Element _pubDateE = (Element) entry .getElementsByTagName("pubDate").item(0); Element _linkE = (Element) entry.getElementsByTagName( "link").item(0); String _title = _titleE.getFirstChild().getNodeValue(); String _category = _categoryE.getFirstChild().getNodeValue(); Date _pubDate = new Date(_pubDateE.getFirstChild().getNodeValue()); String _link = _linkE.getFirstChild().getNodeValue(); //create RssItemObject and add it to the ArrayList RssItem rssItem = new RssItem(_title, _category, _pubDate, _link); rssItems.add(rssItem); conn.disconnect(); }

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  • Problems reading text file data in Java

    - by user1828401
    I have this code: BufferedReader br =new BufferedReader(new FileReader("userdetails.txt")); String str; ArrayList<String> stringList = new ArrayList<String>(); while ((str=br.readLine())!=null){ String datavalue [] = str.split(","); String category = datavalue[0]; String value = datavalue[1]; stringList.add(category); stringList.add(value); } br.close(); it works when the variables category and value do not have a comma(,),however the values in the variable value does contain commas.Is there a way that I can split the index of the without using comma?

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  • Overload and hide methods in Java

    - by Marco
    Hi, i have an abstract class BaseClass with a public insert() method: public abstract class BaseClass { public void insert(Object object) { // Do something } } which is extended by many other classes. For some of those classes, however, the insert() method must have additional parameters, so that they instead of overriding it I overload the method of the base class with the parameters required, for example: public class SampleClass extends BaseClass { public void insert(Object object, Long param){ // Do Something } } Now, if i instantiate the SampleClass class, i have two insert() methods: SampleClass sampleClass = new SampleClass(); sampleClass.insert(Object object); sampleClass.insert(Object object, Long param); what i'd like to do is to hide the insert() method defined in the base class, so that just the overload would be visible: SampleClass sampleClass = new SampleClass(); sampleClass.insert(Object object, Long param); Could this be done in OOP?

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  • High performance distributed asynchronous RPC in java

    - by unludo
    I would like to do RPC to a list of clients with the following requirements: the server does not know the clients (implies a kind of broker?) and the cleints do not know the server there may be several clients - they share the load to treat the RPC The RPC is asynchronous very fast (round-trip < 1ms) optional : offers a fail-over mechanism. It can be done with underlying tools which are not really intended for that (Hazelcast is an example). What would you use for such requirements? Thanks!

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  • What is the best way to automated (integration) test with java with OpenId4Java against real OpenIdP

    - by mP
    I would like to do a bit more than manually test my openid glue code which happens to use the openid4java library. My goals would be to be able to run it within my IDE with a bunch of tests using Junit or similar. Selenium & tomcat I was thinking of using selenium and a tomcat but thats not exactly a nice approach as this is a bit heavy and not really lightweight. httpunit A solution with http-unit is incomplete because it doesnt really fit with the redirect to my openid provider, authenticate and redirect back. Perhaps i am wrong but this looks like it could get quite involved just to make sure this works. Mocks My last solution is to mock everything and assume thats its accurate and works. If google or yahoo ever change in some way, then ill have to verify manually. The approach is simple but with a major flaw.

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  • Java iterative vs recursive

    - by user1389813
    Can anyone explain why the following recursive method is faster than the iterative one (Both are doing it string concatenation) ? Isn't the iterative approach suppose to beat up the recursive one ? plus each recursive call adds a new layer on top of the stack which can be very space inefficient. private static void string_concat(StringBuilder sb, int count){ if(count >= 9999) return; string_concat(sb.append(count), count+1); } public static void main(String [] arg){ long s = System.currentTimeMillis(); StringBuilder sb = new StringBuilder(); for(int i = 0; i < 9999; i++){ sb.append(i); } System.out.println(System.currentTimeMillis()-s); s = System.currentTimeMillis(); string_concat(new StringBuilder(),0); System.out.println(System.currentTimeMillis()-s); } I ran the program multiple time, and the recursive one always ends up 3-4 times faster than the iterative one. What could be the main reason there that is causing the iterative one slower ?

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  • Proper usage of Java Weak Reference in case of nested collections

    - by Tong Wang
    I need to define a weak reference Map, whose value is a Set. I use Google collections' MapMaker, like this: Map<Class<? extends Object>, Set<Foo>> map = new MapMaker().weakKeys().weakValues().makeMap(); So, for Set<Foo>, can I use a normal HashSet? Or, do I have to create a weak HashSet, like this: Collections.newSetFromMap(new WeakHashMap<Foo, Boolean>()); And why? Another question, the key of my map is Class objects, when will a Class object become weakly reachable? In other words, what is the lifetime of a Class object? Thanks.

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  • Java, searching within a list of objects?

    - by Rick
    I'm a bit lost on the way to make this happen the fastest. I have a large list of objects that have basic variable attributes (with getters / setters) and I need to do a search in this list to find the objects within the list that match a given parameter I have found how to do a regular list search but I need to, for example search for the value of the result of doing a call getName() for each object in the list and get objects that have a result that matches my input. Something like below where the third argument is the result of the method call and the second is what I am trying to find. int index = Collections.binarySearch(myList, "value", getName()); Any advice is appreciated

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  • Dynamically assembling SQL queries in Java

    - by kd
    What is the best way to assemble an SQL query with join conditions dynamically? I don't want to hard code the query for each different condition on a webpage or a set of webpages. Is it even feasible? I got as far as being able to assemble simple queries but i got stumped when i needed to insert join conditions, i.e. how to figure out dependencies for joins etc.

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  • Java - problems with polymorphism

    - by cc0
    I have a book class, then a novel- and a science book class that extend the book class. I made an ArrayList using the book class, then inserted the novels and the science books into that. Now I'm trying to iterate through the ArrayList to count how many novels are there. How can I tell? Would love to see some examples of this! I've been at it for a while.

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  • -Java- Swing GUI - Moving around components specifically with layouts

    - by Xemiru Scarlet Sanzenin
    I'm making a little test GUI for something I'm making. However, problems occur with the positioning of the panels. public winInit() { super("Chatterbox - Login"); try { UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); } catch(ClassNotFoundException e) { } catch (InstantiationException e) { } catch (IllegalAccessException e) { } catch (UnsupportedLookAndFeelException e) { } setSize(300,135); pn1 = new JPanel(); pn2 = new JPanel(); pn3 = new JPanel(); l1 = new JLabel("Username"); l2 = new JLabel("Password"); l3 = new JLabel("Random text here"); l4 = new JLabel("Server Address"); l5 = new JLabel("No address set."); i1 = new JTextField(10); p1 = new JPasswordField(10); b1 = new JButton("Connect"); b2 = new JButton("Register"); b3 = new JButton("Set IP"); l4.setBounds(10, 12, getDim(l4).width, getDim(l4).height); l1.setBounds(10, 35, getDim(l1).width, getDim(l1).height); l2.setBounds(10, 60, getDim(l2).width, getDim(l2).height); l3.setBounds(10, 85, getDim(l3).width, getDim(l3).height); l5.setBounds(l4.getBounds().width + 14, 12, l5.getPreferredSize().width, l5.getPreferredSize().height); l5.setForeground(Color.gray); i1.setBounds(getDim(l1).width + 15, 35, getDim(i1).width, getDim(i1).height); p1.setBounds(getDim(l1).width + 15, 60, getDim(p1).width, getDim(p1).height); b1.setBounds(getDim(l1).width + getDim(i1).width + 23, 34, getDim(b2).width, getDim(b1).height - 5); b2.setBounds(getDim(l1).width + getDim(i1).width + 23, 60, getDim(b2).width, getDim(b2).height - 5); b3.setBounds(getDim(l1).width + getDim(i1).width + 23, 10, etDim(b2).width, getDim(b3).height - 5); b1.addActionListener(clickButton); b2.addActionListener(clickButton); b3.addActionListener(clickButton); pn1.setLayout(new FlowLayout(FlowLayout.RIGHT)); pn2.setLayout(new FlowLayout(FlowLayout.RIGHT)); pn1.add(l1); pn1.add(i1); pn1.add(b1); pn2.add(l2); pn2.add(p1); pn2.add(b2); add(pn1); add(pn2); } I am attempting to use FlowLayout to position the panels in the way desired. I'd use BorderLayout while adding, but the vertical spacing is too far away when I just use directions closest to one another. The output of this code is to create a window, 300,150, place whatever's in the two panels in the exact same spaces. Yes, I realize there's useless code there with setBounds(), but that was just me screwing around with Absolute Positioning, which wasn't working out for me either.

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  • java for loop not working

    - by Steve
    I hope this isn't a stupid question but I have looked up every example I can find and it still seems like I have this code right and it still isn't working... I enter one number and it moves on to the next line of code instead of looping. I'm using this to fill an array with user input numbers. I appreciate any help, thanks. for(i=0; i<9; i++); { System.out.println ("Please enter a number:"); Num[i] = keyboard.nextDouble(); Sum += Num[i]; Product *= Num[i]; }

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  • Java giving incorrect year values

    - by whistler
    Something very, very strange is occurring in my program, and I'm wondering if anyone out there has seen this occur before. And, if so, how to fix it. Basically, I am parsing an csv file...no problem there. One column contains a date and I am taking it in as a String and changing to a Date object. Again, no problem there. The code is as follows: SimpleDateFormat dateFormat = new SimpleDateFormat("MM/dd/yy hh:mm"); Date initialDate = new Date(); try { initialDate = dateFormat.parse(rows.get(0)[8]); System.out.println(initialDate); } catch (ParseException e) { // TODO Auto-generated catch block e.printStackTrace(); } Of course, I'm parsing other columns as well (and those are working fine). So, when I run my program for a small csv file (2.8 MB), the dates come out (i.e. are parsed) perfectly. However, when I run the program for a large csv file (25 MB), the dates are a hot mess. For example, take a look at the year values I am getting (the following is just a tiny portion of the println output from the code above): 1000264 at Sun Nov 05 15:30:00 EST 2186 1000320 at Sat Mar 04 17:30:00 EST 2169 1000347 at Sat Apr 01 09:45:00 EDT 2169 1000413 at Tue Jul 09 13:00:00 EDT 2182 1000638 at Fri Dec 11 13:45:00 EST 2167 1000667 at Wed Dec 10 10:00:00 EST 2188 1000690 at Mon Jan 02 13:00:00 EST 2169 1000843 at Thu Feb 11 13:30:00 EST 2196 In actuality, the years are in the realm of 1990-2006 or so. Again, this does not happen with the small csv file. Does anyone know what's going on here and how I can fix it? I need to process the large csv file (the small one was just for testing purposes). By request, here are the actual dates in the csv file and after that the value given by the code above: 5/20/03 15:30 5/20/03 15:30 8/30/04 9:00 8/30/04 9:00 12/20/04 10:30 12/20/04 10:30 Sun Nov 05 15:30:00 EST 2186 Sun Nov 05 15:30:00 EST 2186 Sun Nov 05 15:30:00 EST 2186 Thu Dec 08 09:00:00 EST 2196 Tue Dec 12 10:30:00 EST 2186 Tue Dec 12 10:30:00 EST 2186

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  • Need a Java based interruptible timer thread

    - by LambeauLeap
    I have a Main Program which is running a script on the target device(smart phone) and in a while loop waiting for stdout messages. However in this particular case, some of the heartbeat messages on the stdout could be spaced almost 45secs to a 1minute apart. something like: stream = device.runProgram(RESTORE_LOGS, new String[] {}); stream.flush(); String line = stream.readLine(); while (line.compareTo("") != 0) { reporter.commentOnJob(jobId, line); line = stream.readLine(); } So, I want to be a able to start a new interruptible thread after reading line from stdout with a required a sleep window. Upon being able to read a new line, I want to be able to interrupt/stop(having trouble killing the process), handle the newline of stdout text and restart a process. And it the event I am not able to read a line within the timer window(say 45secs) I want to a way to get out of my while loop either. I already tried the thread.run, thread.interrupt approach. But having trouble killing and starting a new thread. Is this the best way out or am I missing something obvious?

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  • Java blocking socket returning incomplete ByteBuffer

    - by evandro-carrenho
    I have a socketChannel configured as blocking, but when reading byte buffers of 5K from this socket, I get an incomplete buffer sometimes. ByteBuffer messageBody = ByteBuffer.allocate(5*1024); messageBody.mark(); messageBody.order(ByteOrder.BIG_ENDIAN); int msgByteCount = channel.read(messageBody); Ocasionally, messageBody is not completely filled and channel.read() does not return -1 or an exception, but the actual number of bytes read (which is less than 5k). Has anyone experienced a similar problem?

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  • Java order jlist by status

    - by Takami
    i have a small problem, i don't know how to sort my jlist by status which is retrieved from database. i want sort by "online" and "offline", i mean online computers go first and then offline computers, i have this code now, it just makes the icon+text for the jlist Can you tell me how can i filter/sortby status? public void acx_pc(String query) { try { Statement st = con.createStatement(); ResultSet rs = st.executeQuery(query); String comb; Map<Object, Icon> icons = new HashMap<>(); ArrayList<String> pc_list = new ArrayList<>(); int i = 0; while (rs.next()) { //Getting info from DB String pc_name = rs.getString("nombre_pc"); String pc_ip = rs.getString("IP"); String status = rs.getString("estado"); //Setting text for the jList comb = pc_name + " - " + pc_ip; //Comparing Status switch (status) { case "online": //This is just for rendering an image+text to Jlist icons.put(comb, new ImageIcon(getClass().getResource("/Imagenes/com_on_30x30.png"))); break; case "offline": //This is just for rendering an image to Jlist icons.put(comb, new ImageIcon(getClass().getResource("/Imagenes/com_off_30x30.png"))); break; } //Adding info to ArrayList pc_list.add(i, comb); i++; } con.close(); // Setting the list/text on Jlist Home.computer_jlist.setListData(pc_list.toArray()); // create a cell renderer to add the appropriate icon Home.computer_jlist.setCellRenderer(new pc_cell_render(icons)); } catch (Exception e) { System.out.println("Error aqui: " + e); } } I want to do something like (should automatically order) http://imageshack.us/a/img27/9018/2mx1.png and not: http://imageshack.us/a/img407/346/e9r.png

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  • Bizzare Java invalid Assignment Operator Error

    - by Kay
    public class MaxHeap<T extends Comparable<T>> implements Heap<T>{ private T[] heap; private int lastIndex; private static final int defaultInitialCapacity = 25; public void add(T newItem) throws HeapException{ if (lastIndex < Max_Heap){ heap[lastIndex] = newItem; int place = lastIndex; int parent = (place – 1)/2; //ERROR HERE********** while ( (parent >=0) && (heap[place].compareTo(heap[parent])>0)){ T temp = heap[place]; heap[place] = heap[parent]; heap[parent] = temp; place = parent; parent = (place-1)/2; }else { throw new HeapException(“HeapException: Heap full”); } } } Eclipse complains that there is a: "Syntax error on token "Invalid Character", invalid AssignmentOperator" With the red line beneath the '(place-1)' There shouldn't be an error at all since it's just straight-forward arithmetic. Or is it not that simple?

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  • Need Java Swing equivalent of "scrollIntoView" from Browser DOM

    - by bgould
    I have a JPanel with several levels of child components, also with a JScrollPane. I'm placing a focus listener on some of the child components to add some behavior to those components, but I would also like to have that component scroll into the JPanel's viewport when focus is gained. My question is, does anyone have a general purpose function to do this, similar to the browser DOM function "scrollIntoView"? I've tried muddling through this with various inputs to JComponent.scrollRectToVisible but I guess I haven't figured out the magic word. Thanks in advance.

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