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  • Concurrent Programming:Should I write a sequential program first, then add thread safety?

    - by evthim
    I'm working on a project where we have to create a number of threads(actual number will be inputted in by testers (TA's)). I'm having trouble not only with the programming but also with the design, I can't wrap my head around all of the threads that will be invoked and where I might cause errors. The project is due soon so I don't want to waste time on this if it'll actually set me back, but I was wondering if I should write the program like only one thread will be running and everything should be sequential and then later go back and try to add the thread safety parts of the code? Would that take twice the original amount of time? Project Description: Note:I'm going to be as vague as possible so I don't violate any honor codes, sorry :( your program should accept n number of objectA threads, m number of objectB threads, and r number of objectC objectB threads interact with code in objectA. objectA threads interact with code in objectB and objectC objectB and objectC don't directly interact, but do so indirectly through objectA -ex: objectB needs something from objectA. objectA gets the result for that something by calling objectC my confusion stems mostly from the fact that all of this interactions will be done by m+n threads and there are various restrictions throughout the descriptions, like objectB can request something from objectA, and objectA has to wait for objectC to finish that something before returning it to objectB. Also each objectA thread can only work on one instruction from objectB at a time, etc. etc. I just want to know if I write the code so that there is only 1 objectA, 1 objectB and 1 object C, can I go back and easily modify it so that those 1's can be changed to m, n and r? Sorry again, if my description is a little bit confusing.

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  • Threadsafe way of exposing keySet()

    - by Jake
    This must be a fairly common occurrence where I have a map and wish to thread-safely expose its key set: public MyClass { Map<String,String> map = // ... public final Set<String> keys() { // returns key set } } Now, if my "map" is not thread-safe, this is not safe: public final Set<String> keys() { return map.keySet(); } And neither is: public final Set<String> keys() { return Collections.unmodifiableSet(map.keySet()); } So I need to create a copy, such as: public final Set<String> keys() { return new HashSet(map.keySet()); } However, this doesn't seem safe either because that constructor traverses the elements of the parameter and add()s them. So while this copying is going on, a ConcurrentModificationException can happen. So then: public final Set<String> keys() { synchronized(map) { return new HashSet(map.keySet()); } } seems like the solution. Does this look right?

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  • how to add classes to build path in eclipse

    - by akshay
    I have used the folllowing steps to add classes to my build path still i am geting errors as import not resolved.I had followed the following steps. Select Create New Folder and name it TpmWebUIClasses. Click the Advanced button and select the Link to folder in the file system check box. Browse for to the folder where you have copied the classes Make sure the selected folder is listed and then click OK. How can i resolve the error?

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  • Headless build of eclipse features - PDE Tools or Buckminster?

    - by Max
    I am trying to set up a headless build for a big eclipse feature, containing other features and plugins. As some needed plugins are generated using GMF and EMF, the build workflow must be something like this: SVN Check-out Invoke Generation Run Tests Build all Publish update-site Over the last couple of weeks, i played around with PDE Headless Build and Buckminster. Anyhow i still got problems with both and can't decide on which i should spent my effort. So what would you prefer? What experience you made? Anybody out there who needed to set up a similiar workflow before? Thank you for all answers :)

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  • How to expose an entity via alternate keys with spring data rest

    - by dan carter
    Spring-data-rest does a great job exposing entities via their primary key for GET, PUT and DELETE etc. operations. /myentityies/123 It also exposes search operations. /myentities/search/byMyOtherKey?myOtherKey=123 In my case the entities have a number of alternate keys. The systems calling us, will know the objects by these IDs, rather than our internal primary key. Is it possible to expose the objects via another URL and have the GET, PUT and DELETE handled by the built-in spring-data-rest controllers? /myentities/myotherkey/456 We'd like to avoid forcing the calling systems to have to make two requests for each update. I've tried playing with @RestResource path value, but there doesn't seem to be a way to add additional paths.

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  • Does collections type conversion util methods already exist in any API?

    - by Delta
    interface TypeConverter<T, E> { T convert(E e); } class CollectionUtil() { public static <E> List<T> convertToList(List<E> fromList, TypeConverter<T, E> conv) { { if(fromList== null) return null; List<T> newList = new ArrayList<T>(fromList.size()) for(E e : fromList) { newList.add(conv.convert(e)); } return newList; } } Above code explains converting from List of String to List of Integer by implementing TypeConverter interface for String, Integer. Are there already any collections conversion utility methods exists in any API like list to set and so on?

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  • Calculated group-by fields in MongoDB

    - by Navin Viswanath
    For this example from the MongoDB documentation, how do I write the query using MongoTemplate? db.sales.aggregate( [ { $group : { _id : { month: { $month: "$date" }, day: { $dayOfMonth: "$date" }, year: { $year: "$date" } }, totalPrice: { $sum: { $multiply: [ "$price", "$quantity" ] } }, averageQuantity: { $avg: "$quantity" }, count: { $sum: 1 } } } ] ) Or in general, how do I group by a calculated field?

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  • Android Force Recycle Large Bitmap?

    - by GuyNoir
    From another stackoverflow question, it seems that Android handles large bitmaps differently than other memory. It also seems like there is a way to force Android to recycle the bitmaps to free up memory. Can anyone enlighten me on how to do this. My application uses 2-6 huge bitmaps at all times, so it nearly kills the phone's memory when running, and I want to clear it up when the user quits.

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  • How can I load a property lazily in JDO (on Google App Engine)?

    - by luciano
    I have this code in one of my @PersistenceCapable classes: @Persistent private Blob data; The Blob can be quite big, so I'd like to load it lazily since most of the times I don't need it. How can I annotate that property to avoid immediate loading? I could create another class that contains the Blob alone and then use a lazy one-to-one, but I'd like to solve this with annotations.

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  • Spring MVC - JSP - Place to Store Environment Specific Constants

    - by jboyd
    Where in the Spring-MVC/JSP application would you store things that need to be accessed by both the controllers and views such as environment specific base_url's, application ids to be used in javascript and so on? I've tried creating an application scoped bean and then at the top of my JSPs, but that doesn't seem to be working. <!-- Environment --> <bean id="myEnv" class="com.myapp.MyAppEnvironment" scope="application"> <property name="baseUrl" value="http://localhost:8080/myapp/"/> <property name="videoPlayerId" value="234346565"/> </bean> And using it in the following manner <jsp:useBean id="myEnv" scope="application" type="com.myapp.MyAppEnvironment"/>

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  • Encrypt string with public key only

    - by vlahovic
    i'm currently working on a android project where i need to encrypt a string using 128 bit AES, padding PKCS7 and CBC. I don't want to use any salt for this. I've tried loads of different variations including PBEKey but i can't come up with working code. This is what i currently have: String plainText = "24124124123"; String pwd = "BobsPublicPassword"; byte[] key = pwd.getBytes(); key = cutArray(key, 16); byte[] input = plainText.getBytes(); byte[] output = null; SecretKeySpec keySpec = null; keySpec = new SecretKeySpec(key, "AES"); Cipher cipher = Cipher.getInstance("AES/CBC/PKCS7Padding"); cipher.init(Cipher.ENCRYPT_MODE, keySpec); output = cipher.doFinal(input); private static byte[] cutArray(byte[] arr, int length){ byte[] resultArr = new byte[length]; for(int i = 0; i < length; i++ ){ resultArr[i] = arr[i]; } return resultArr; } Any help appreciated //Vlahovic

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  • Where should I initialize variables for an OO Recursive Descent Parse Tree?

    - by Vasto
    I'd like to preface this by stating that this is for a class, so please don't solve this for me. One of my labs for my cse class is creating an interpreter for a BNF that was provided. I understand most of the concepts, but I'm trying to build up my tree and I'm unsure where to initialize values. I've tried in both the constructor, and in the methods but Eclipse's debugger still only shows the left branch, even though it runs through completely. Here is my main procedure so you can get an idea of how I'm calling the methods. public class Parser { public static void main(String[] args) throws IOException { FileTokenizer instance = FileTokenizer.Instance(); FileTokenizer.main(args); Prog prog = new Prog(); prog.ParseProg(); prog.PrintProg(); prog.ExecProg(); } Now here is My Prog class: public class Prog { private DeclSeq ds; private StmtSeq ss; Prog() { ds = new DeclSeq(); ss = new StmtSeq(); } public void ParseProg() { FileTokenizer instance = FileTokenizer.Instance(); instance.skipToken(); //Skips program (1) // ds = new DeclSeq(); ds.ParseDS(); instance.skipToken(); //Skips begin (2) // ss = new StmtSeq(); ss.ParseSS(); instance.skipToken(); } I've tried having Prog() { ds = null; ss = null; } public void ParseProg() { FileTokenizer instance = FileTokenizer.Instance(); instance.skipToken(); //Skips program (1) ds = new DeclSeq(); ds.ParseDS(); ... But it gave me the same error. I need the parse tree built up so I can do a pretty print and an execute command, but like I said, I only get the left branch. Any help would be appreciated. Explanations why are even more so appreciated. Thank you, Vasto

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  • Scanner cuts off my String after about 2400 characters

    - by Ventrue
    I've got some very basic code like while (scan.hasNextLine()) { String temp = scan.nextLine(); System.out.println(temp); } where scan is a Scanner over a file. However, on one particular line, which is about 6k chars long, temp cuts out after something like 2470 characters. There's nothing special about when it cuts out; it's in the middle of the word "Australia." If I delete characters from the line, the place where it cuts out changes; e.g. if I delete characters 0-100 in the file then Scanner will get what was previously 100-2570. I've used Scanner for larger strings before. Any idea what could be going wrong?

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  • Problem in setting backgound color to my TreeCellRenderer

    - by Sunil Kumar Sahoo
    Hi I have cretaed my own renderer. I want the back ground should be blue. I have set background color as blue also. But I donot know what is tha problem that the background color of my renderer always seems to be white. I have post the code. please help where I am wrong so that the background color becomes white. class CheckTreeCellRenderer extends JPanel implements TreeCellRenderer { private CheckTreeSelectionModel selectionModel; private MyRenderer delegate; private TristateCheckBox checkBox = new TristateCheckBox("", null, true); public static final State NOT_SELECTED = new State(); public static final State SELECTED = new State(); public static final State DONT_CARE = new State(); public CheckTreeCellRenderer(MyRenderer delegate, CheckTreeSelectionModel selectionModel) { this.delegate = delegate; this.selectionModel = selectionModel; setLayout(new BorderLayout()); setOpaque(true); setBackground(new Color(207, 219, 234)); checkBox.setState(Boolean.TRUE); checkBox.setOpaque(true); checkBox.setBackground(new Color(207, 219, 234)); } public Component getTreeCellRendererComponent(JTree tree, Object value, boolean selected, boolean expanded, boolean leaf, int row, boolean hasFocus) { Component renderer = delegate.getTreeCellRendererComponent(tree, value, selected, expanded, leaf, row, hasFocus); TreePath path = tree.getPathForRow(row); if (path != null) { if (selectionModel.isPathSelected(path, true)) { checkBox.setState(Boolean.TRUE); } else { checkBox.setState(selectionModel.isPartiallySelected(path) ? null : Boolean.FALSE); } } renderer.setBackground(new Color(207, 219, 234)); tree.setOpaque(true); tree.setBackground(new Color(207, 219, 234)); this.setOpaque(true); this.setBackground(new Color(207, 219, 234)); add(checkBox, BorderLayout.WEST); add(renderer, BorderLayout.CENTER); return this; } }

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  • How to launch a web server and point the browser to it when it finishes?

    - by Wing C. Chen
    I am writing a windows batch file to do the following things: Display a picture in the middle of the screen, showing the beautiful icon of my software. Kick of the launch of the web server. Finish displaying the picture. Point the browser to the start page. I have already know how to do it in step 2 and 4. However, I have the following questions in writing the windows batch file: 1. How do I know that the launch of the web server is finished, taking jetty as the example? 2. How do I display a picture and stop displaying it when I want to? Here is what I have got so far: ::here I would like to display the picture start javaw -jar start.jar ::Starting jetty here ::here I would like to stop displaying the picture start http://localhost:8080/myApp ::Pointing the browser to the page Thank you in advance for your help.

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  • How to set default values to all wrong or null parameters of method?

    - by Roman
    At the moment I have this code (and I don't like it): private RenderedImage private RenderedImage getChartImage (GanttChartModel model, String title, Integer width, Integer height, String xAxisLabel, String yAxisLabel, Boolean showLegend) { if (title == null) { title = ""; } if (xAxisLabel == null) { xAxisLabel = ""; } if (yAxisLabel == null) { yAxisLabel = ""; } if (showLegend == null) { showLegend = true; } if (width == null) { width = DEFAULT_WIDTH; } if (height == null) { height = DEFAULT_HEIGHT; } ... } How can I improve it? I have some thoughts about introducing an object which will contain all these parameters as fields and then, maybe, it'll be possible to apply builder pattern. But still don't have clear vision how to implement that and I'm not sure that it's worth to be done. Any other ideas?

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  • GWT: What is the way to handle Click on GWT FlowPanel

    - by shaman.sir
    May be a dumb question, but GWT FlowPanel (raw div element) does not provides something to handle a mouseclick/mousemovement on it. Overriding onBrowserEvent do not works either. If setting onclick event using native JavaScript (need to specify positive height before, 'div' have a height of 0 if not specified), then catching these events is working properly. Is there a way to do it without using JSNI?

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  • How to call superconstructor in a neat way

    - by sandis
    So here is my code: public MyClass (int y) { super(y,x,x); //some code } My problem is that in this case i want to generate a 'x' and sent to the super constructor. However the call to the superconstructor must be the first line in this constructor. Of course I could do something like this: int x; { x = generateX(); } But this feels ugly, and then the code will run no matter what constructor I use, which feels not so nice. Right now I am consider encapsulating my whole object in another object that only calculates x and then starts this object. Is this the best approach?

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  • How can I use BeanUtils copyProperties to copy from boolean to Boolean?

    - by carrier
    BeanUtils copyProperties, out of the box, doesn't seem to handle copying from Boolean object properties to boolean primitive properties. I figured I could create and register a converter to handle this, but that just didn't seem to work. So, how can I use BeanUtils to copy the properties from class Source to class Destination where: public class Destination { private boolean property; public boolean isProperty() { return property; } public void setProperty(boolean property) { this.property = property; } } public class Source{ private Boolean property; public Boolean getProperty() { return property; } public void setProperty(Boolean property) { this.property = property; } }

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