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• How to use locks/synchronization here

  - by MasterGberry

  I have this code block here and i need to make sure the rankedPlayersWaitingForMatch is synchronized between threads properly. I was going to use synchronize but that i don't think will work here because of the variable being used in the if statement. I read online about final Lock lock = new ReentrantLock(); but I am a bit confused on how to use it in this case properly with the try/finally block. Can I get a quick example? Thanks // start synchronization if (rankedPlayersWaitingForMatch.get(rankedType).size() >= 2) { Player player1 = rankedPlayersWaitingForMatch.get(rankedType).remove(); Player player2 = rankedPlayersWaitingForMatch.get(rankedType).remove(); // end synchronization // ... I don't want this all to be synchronized, just after the first 2 remove() } else { // end synchronization // ... }

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• Can i never reference any external 3rd party jar in my independent ejb module?

  - by Nitesh Panchal

  Hello, Can we never refer any external 3rd party jar in independent ejb module (except copying the jar file in our appserver/lib)? This seems so illogical doesn't it? I don't want to create a Enterprise application. Why am i being forced to create an Enterprise application if i have to use any jar files? Are there no alternatives available?

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• Advantages of using a Dynamic Client with JAX-WS

  - by jconlin

  What are the advantages of using a dynamic client with JAX-WS services as opposed to just using generated client classes? What are the disadvantages? **For my particular case I am using Apache CXF, I'm not sure what other libraries allow "dynamic" clients. -I thought I didn't need to add this, but... I'm looking for non-obvious(I know...subjective) advantages. I don't need someone else to tell me that an advantage of not using generated classes is that I don't need to generate classes.

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• code for searching from file using GUI

  - by maya

  hi everyone, I'm looking for a code that allows me to search from file , for example, in my program which is shoes shop's program . I should design and implement interfaces which have to search data from file TXT. the idea is that when I choose one item like type of shoes the program should display all other times such as color, size and price . Thanks in advance.

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• Why are static imports of static methods with same names legal?

  - by user1055638

  Lets say we have these packages and classes: package p1; public class A1 { public static void a() {} } package p2; public class A1 { public static void a() {} } package p3; import static p1.A1.a; import static p2.A1.a; public class A1 { public static void test() { } } I am wondering, why the static import of methods is legal (won't result in compile time error) in package p3? We won't be able to use them further in the test() method as such usage will result in the compile time error. Why it is not the same as with a normal import of classes. Lets say we would like to import classes A1 from packages p1 and p2 into p3: package p3; import p1.A1; import p2.A1; such import is illegal and will result in the compile time error.

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• Android app crashes on Async Task

  - by Telmo Vaz

  why is my APP crashing when I invoke the AsyncTask? public class Login extends Activity { String mail; EditText mailIn; Button btSubmit; @Override protected void onCreate(Bundle tokenArg) { super.onCreate(tokenArg); setContentView(R.layout.login); mailIn = (EditText)findViewById(R.id.usermail); btSubmit = (Button)findViewById(R.id.submit); btSubmit.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View thisView) { new LoginProc().execute(); } }); } public class LoginProc extends AsyncTask<String, Void, Void> { @Override protected void onPreExecute() { mailIn = (EditText)findViewById(R.id.usermail); mail = mailIn.getText().toString(); super.onPreExecute(); } @Override protected Void doInBackground(String... params) { Toast.makeText(getApplicationContext(), mail, Toast.LENGTH_SHORT).show(); return null; } } } I'm trying to make the String name get it's value on the preExecute method, but it happens that the app crashes on that point. Even if I take the preExecute and do that on the doInBrackground, it still crashes. What's wrong?

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• How can I get the name of all tables in a JavaDB database?

  - by Jonas

  How can i programmatically get the names of all tables in a JavaDB database? Is there any specific SQL-statement over JDBC I can use for this or any built in function in JDBC? I will use it for exporting the tables to XML, and would like to do it this way so I don't miss any tables from the database when exporting.

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• Encountering NullPointerException when trying to add polynoms

  - by Ayler Cruz

  I need to add two polynomials, which is composed of two ints. For example, the coefficient and the exponent 3x^2 would be constructed using 3 and 2 as parameters. I am getting a NullPointerException but I can't figure out why. Any help would be appreciated! public class Polynomial { private Node poly; public Polynomial() { } private Polynomial(Node p) { poly = p; } private class Term { int coefficient; int exponent; private Term(int coefficient, int exponent) { this.coefficient = coefficient; this.exponent = exponent; } } private class Node { private Term data; private Node next; private Node(Term data, Node next) { this.data = data; this.next = next; } } public void addTerm(int coeff, int exp) { Node pointer = poly; if (pointer.next == null) { poly.next = new Node(new Term(coeff, exp), null); } else { while (pointer.next != null) { if (pointer.next.data.exponent < exp) { Node temp = new Node(new Term(coeff, exp), pointer.next.next); pointer.next = temp; return; } pointer = pointer.next; } pointer.next = new Node(new Term(coeff, exp), null); } } public Polynomial polyAdd(Polynomial p) { return new Polynomial(polyAdd(this.poly, p.poly)); } private Node polyAdd(Node p1, Node p2) { if (p1 == p2) { Term adding = new Term(p1.data.coefficient + p2.data.coefficient, p1.data.exponent); p1 = p1.next; p2 = p2.next; return new Node(adding, null); } if (p1.data.exponent > p2.data.exponent) { p2 = p2.next; } if (p1.data.exponent < p2.data.exponent) { p1 = p1.next; } if (p1.next != null && p2.next != null) { return polyAdd(p1, p2); } return new Node(null, null); } }

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• JSP template inheritance

  - by Ryan

  Coming from a background in Django, I often use "template inheritance", where multiple templates inherit from a common base. Is there an easy way to do this in JSP? If not, is there an alternative to JSP that does this (besides Django on Jython that is :) base template <html> <body> {% block content %} {% endblock %} </body> <html> basic content {% extends "base template" %} {% block content %} <h1>{{ content.title }} <-- Fills in a variable</h1> {{ content.body }} <-- Fills in another variable {% endblock %} Will render as follows (assuming that conten.title is "Insert Title Here", and content.body is "Insert Body Here") <html> <body> <h1>Insert title Here <-- Fills in a variable</h1> Insert Body Here <-- Fills in another variable </body> <html>

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• Alternatives to static variables in Android

  - by Mocha

  I am using static Arrays and HashMaps to store some values in my AppWidgetProvider class. But they are becoming null when the process dies, so the widget does not work anymore. Are there any alternatives to using static members to store data for an AppWidgetProvider in Android?

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• Child Activity in Android

  - by Martin Marinov

  So I have two Activities. The main is called Main, and the child one is called Child. When a button is clicked in the main activity it triggers the following piece of code: Intent i = new Intent(Main.this, Child.class); Main.this.startActivity(i); That opens the Child activity. As soon as I call finish() or press the back button within the child activity instead of going back to the main one, the app just closes. Can you give me a hint where the problem might be :( P.S. By trial and error I found out that if edit AndroidManifest.xml and add android:theme="@android:style/Theme.Dialog" within the declaration of Child the back button and calling finish() behaves as expected: closes the child activity and brings the main into focus. The problem is that when I start typing in an EditText the screen starts flickering (rather bizzare). So I can't use it as a dialog. My main activity uses the camera, so that might be making problems. Although when the child activity is started, the onPause event is fired and it stops the camera until onResume is called.

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• add Component to JPanel

  - by jouzef19

  Hi , I am using netBeans editor to create desktop application . and i want to add Component without using drag and drop way. I am trying code like this for adding JList to JPanel but nothing showed JList jl = new JList(); Vector<String> v= new Vector<String>(); v.add("one"); v.add("Two"); v.add("Three"); jl.setListData(v); JScrollPane js = new JScrollPane(jl); js.setLocation(50, 50); js.setSize(100, 100); js.setVisible(true); jPanel1.add(js);

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• Stacking a View with the Editor Area?

  - by Patrick

  Hello everybody, :-) Is it possible, when developing an Eclipse RCP Application, to stack a view with the editor area? Like this? http://www.fotos-hochladen.net/stackingaviewwithane9e1fdbvp.png I have multiple lists / tables. I want to create a kind of preview composite. When an Item on a list is selected by single mouse click, i want my preview composite to show the data of the item. If the user double clicks an item, i want to open an editor in the stack behind the preview composite. Is there anyway to achieve this? Thanks Patrick :-)

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• for loop will not loop

  - by Bjørn Jostein Aurheim

  I have a for loop that I will use to compute time intervals to add to an ArrayList. The problem is that I can not prove that the for loop is being executed. Nothing is printed when using the system.out.println() statement, and nothing is added to the array from inside the loop ... any sugestions? // lager tidspunkter og legger disse inn i en Array kalt tider tid.setTimer(16); tid.setMinutter(0); tid.setSekunder(0); tider.add(tid.asString());// String "16:00" is added as it should System.out.println("tiden er: "+tid.asString());// gives 16:00 printed for(int i=0;i>12;i++){ System.out.println("er i løkken");// gives nothing printed tid.increaseMinutter(30); System.out.println(tid.asString());// gives nothing printed tider.add(tid.asString()); }

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• Is it bad practice to change state inside of an if statement?

  - by Benjamin

  I wrote some code that looks similar to the following: String SKIP_FIRST = "foo"; String SKIP_SECOND = "foo/bar"; int skipFooBarIndex(String[] list){ int index; if (list.length >= (index = 1) && list[0].equals(SKIP_FIRST) || list.length >= (index = 2) && (list[0] + "/" + list[1]).equals(SKIP_SECOND)){ return index; } return 0; } String[] myArray = "foo/bar/apples/peaches/cherries".split("/"); print(skipFooBarIndex(myArray); This changes state inside of the if statement by assigning index. However, my coworkers disliked this very much. Is this a harmful practice? Is there any reason to do it?

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• Question about factory classes

  - by devoured elysium

  Currently I have created a ABCFactory class that has a single method creating ABC objects. Now that I think of it, maybe instead of having a factory, I could just make a static method in my ABC Method. What are the pro's and con's on making this change? Will it not lead to the same? I don't foresee having other classes inherit ABC, but one never knows! Thanks

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• How to get result size from an SQL query and check size

  - by Jimmy

  Hi I'm trying to write a piece of code for a simple verification method as part of a MVC. At present the SQL is not written as a prepared statement so obviously it is at risk to a SQL injection so any help in regards to writing the SQL as a prepared statement would be really helpful. The method which is in the User model. public boolean getLoginInfo() { try { DBAccess dbAccess = new DBAccess(); String sql = "SELECT username, password FROM owner WHERE username = '" + this.username + "'AND password = '" + this.password + "';"; dbAccess.close();dbAccess.executeQuery(sql); dbAccess.close(); return true; } catch (Exception e) { return false; } } I want to get the size of the result set which is generated by the SQL query and if the size of it is 1 return true else it's false. If you need more info on the rest of the MVC just post and I'll get it up here.

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• Is unnecessary error handling recommended in business logic? eg. Null check/Percentage limit check etc

  - by novice_at_work

  We usually put unnecessary checks in our business logic to avoid failures. Eg. 1. public ObjectABC funcABC(){ ObjectABC obj = new ObjectABC; .......... .......... //its never set to null here. .......... return obj; } ObjectABC o = funABC(); if(o!=null){ //do something } Why do we need this null check if we are sure that it will never be null? Is it a good practice or not? 2. int pplReached = funA(..,..,..); int totalPpl = funB(..,..,..); funA() just puts a few more restriction over result of funB(). Double percentage = (totalPpl==0||totalPpl<pplReached) ? 0.0 : pplReached/totalPpl; Do we again need this check? The questions is: Aren't we swallowing some fundamental issue by putting such checks? Issues which should be shown ideally, are avoided by putting these checks. What is the recommended way?

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• JAXB Annotated class - setting of a variable which is not an element

  - by sswdeveloper

  I have a JAXB annotated class say @XmlRootElement(namespace = "http://www.abc.com/customer") Class Customer{ @XmlElement(namespace = "http://www.abc.com/customer") private String Name; @XmlElement(namespace = "http://www.abc.com/customer") private String Address; @XmlTransient private HashSet set = new HashSet(); public String getName(){ return Name; } public void setName(String name){ this.Name = name; set.add("Name"); } public String getAddress(){ return Address; } public void setAddress(String address){ this.Address = address; set.add("Address"); } public void getSet(){ return set; } I have a XML of the form <?xml version="1.0" encoding="UTF-8" standalone="yes"?> <Customer xmlns="http://www.abc.com/customer" > <Name>Ralph</Name> <Address>Newton Street</Address> </Customer> I use JAXB unmarshalling to get the object representation of the XML input. The values for Name and Address are set correctly. However the value of set gets lost(since it is @XMLTransient it gets ignored) Is there any way of ensuring that it is still set in the object which has been unmarshalled? Some other annotation which I can use?

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• spring mvc forward to jsp

  - by jerluc

  I currently have my web.xml configured to catch 404s and send them to my spring controller which will perform a search given the original URL request. The functionality is all there as far as the catch and search go, however the trouble begins to arise when I try to return a view. <bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver" p:order="1"> <property name="mediaTypes"> <map> <entry key="json" value="application/json" /> <entry key="jsp" value="text/html" /> </map> </property> <property name="defaultContentType" value="application/json" /> <property name="favorPathExtension" value="true" /> <property name="viewResolvers"> <list> <bean class="org.springframework.web.servlet.view.BeanNameViewResolver" /> <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="prefix" value="/WEB-INF/jsp/" /> <property name="suffix" value="" /> </bean> </list> </property> <property name="defaultViews"> <list> <bean class="org.springframework.web.servlet.view.json.MappingJacksonJsonView" /> </list> </property> <property name="ignoreAcceptHeader" value="true" /> </bean> This is a snippet from my MVC config file. The problem lies in resolving the view's path to the /WEB-INF/jsp/ directory. Using a logger in my JBoss setup, I can see that when I test this search controller by going to a non-existent page, the following occurs: Server can't find the request Request is sent to 404 error page (in this case my search controller) Search controller performs search Search controller returns view name (for this illustration, we'll assume test.jsp is returned) Based off of server logger, I can see that org.springframework.web.servlet.view.JstlView is initialized once my search controller returns the view name (so I can assume it is being picked up correctly by the InternalResourceViewResolver) Server attempts to return content to browser resulting in a 404! A couple things confuse me about this: I'm not 100% sure why this isn't resolving when test.jsp clearly exists under the /WEB-INF/jsp/ directory. Even if there was some other problem, why would this result in a 404? Shouldn't a 404 error page that results in another 404 theoretically create an infinite loop? Thanks for any help or pointers! Controller class [incomplete]: @Controller public class SiteMapController { //-------------------------------------------------------------------------------------- @Autowired(required=true) private SearchService search; @Autowired(required=true) private CatalogService catalog; //-------------------------------------------------------------------------------------- @RequestMapping(value = "/sitemap", method = RequestMethod.GET) public String sitemap (HttpServletRequest request, HttpServletResponse response) { String forwardPath = ""; try { long startTime = System.nanoTime() / 1000000; String pathQuery = (String) request.getAttribute("javax.servlet.error.request_uri"); Scanner pathScanner = new Scanner(pathQuery).useDelimiter("\\/"); String context = pathScanner.next(); List<ProductLightDTO> results = new ArrayList<ProductLightDTO>(); StringBuilder query = new StringBuilder(); String currentValue; while (pathScanner.hasNext()) { currentValue = pathScanner.next().toLowerCase(); System.out.println(currentValue); if (query.length() > 0) query.append(" AND "); if (currentValue.contains("-")) { query.append("\""); query.append(currentValue.replace("-", " ")); query.append("\""); } else { query.append(currentValue + "*"); } } //results.addAll(this.doSearch(query.toString())); System.out.println("Request: " + pathQuery); System.out.println("Built Query:" + query.toString()); //System.out.println("Result size: " + results.size()); long totalTime = (System.nanoTime() / 1000000) - startTime; System.out.println("Total TTP: " + totalTime + "ms"); if (results == null || results.size() == 0) { forwardPath = "home.jsp"; } else if (results.size() == 1) { forwardPath = "product.jsp"; } else { forwardPath = "category.jsp"; } } catch (Exception ex) { System.err.println(ex); } System.out.println("Returning view: " + forwardPath); return forwardPath; } }

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• Method with throws Exception: Where is it actually handled?

  - by Esq

  Here is an example code, I am throwing an exception here, it works perfectly fine without the try/catch block of code for some reason. Do I have to handle this inside this method "EntryDelete" or Do I have to handle this where the method is called from? If so can I see an example, what do I have to import in there? What is the acceptable syntax or method to do this? public boolean EntryDelete(int entryId) throws SQLException{ this.open(); kDatabase.delete(kENTRY_TABLE, kENTRY_ENTRY_ID + "=" + entryId, null); this.close(); return true; } Thanks

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• hibernate versioning parent entity

  - by Priit

  Consider two entities Parent and Child. Child is part of Parent's transient collection Child has a ManyToOne mapping to parent with FetchType.LAZY Both are displayed on the same form to a user. When user saves the data we first update Parent instance and then Child collection (both using merge). Now comes the tricky part. When user modifies only Child property on the form then hibernate dirty checking does not update Parent instance and thus does not increase optimistic locking version number for that entity. I would like to see situation where only Parent is versioned and every time I call merge for Parent then version is always updated even if actual update is not executed in db.

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• Using HSQLDB in production environments

  - by lewap

  I want to use HSQLDB in a production environment for stroring some data in memory and for data export using files. Does anybody have experience with using hsqldb in production environments? Is hsqldb treating server resources gracefully and does it cleanup unused resources properly?

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• How to unit-test a Wicket component with AbstractAjaxTimerBehavior?

  - by Juha Syrjälä

  I have a Wicket panel that has AbstractAjaxTimeBehavior, that I'd like to unit test. How can I trigger a ajax event during the unit test that end up calling AbstractAjaxTimeBehavior's .onTimer(AjaxRequestTarget target) method? behavior = new AbstractAjaxTimerBehavior(Duration.seconds(pollingPeriodInSeconds)) { protected void onTimer(AjaxRequestTarget target) { // how to unit test this? } } add(behavior);

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• Swing Timer in Conjunction with Possible Long-running Background Task

  - by javacavaj

  I need to perform a task repeatedly that affects both GUI-related and non GUI-related objects. One caveat is that no action should performed if the previous task had not completed when the next timer event is fired. My initial thoughts are to use a SwingTimer in conjunction with a javax.swing.SwingWorker object. The general setup would look like this. class { timer = new Timer(speed, this); timer.start(); public void actionPerformed(ActionEvent e) { SwingWorker worker = new SwingWorker() { @Override public ImageIcon[] doInBackground() { // potential long running task } @Override public void done() { // update GUI on event dispatch thread when complete } } } Some potential issues I see with this approach are: 1) Multiple SwingWorkers will be active if a worker has not completed before the next ActionEvent is fired by the timer. 2) A SwingWorker is only designed to be executed once, so holding a reference to the worker and reusing (is not?) a viable option. Is there a better way to achieve this?

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