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• Is using the break statement bad practice?

  - by Lchi

  I've been told by professors and peers at my university that using the break statement is bad practice, but through my coursework haven't come up with a great reason why. Those who claim that it is bad say that it's a "get out of jail free card" and that you can always avoid using it. My guesses for why its considered bad would be that you could possibly skip some cleanup code after the break, or similarly exit some control structure in an inconsistent state. Is there any reason why using break is(n't) bad practice?

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• Properly removing an Integer from a List<Integer>

  - by Yuval A

  Here's a nice pitfall I just encountered. Consider a list of integers: List<Integer> list = new ArrayList<Integer>(); list.add(5); list.add(6); list.add(7); list.add(1); Any educated guess on what happens when you execute list.remove(1)? What about list.remove(new Integer(1))? This can cause some nasty bugs. What is the proper way to differentiate between remove(int index), which removes an element from given index and remove(Object o), which removes an element by reference, when dealing with lists of integers? The main point to consider here is the one @Nikita mentioned - exact parameter matching takes precedence over auto-boxing.

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• How to fix IllegalStateException error when trying to update a listview?

  - by Michael Vetrano

  Hi guys, I am trying to get this code to run, but I get an IllegalStateException when I run this code saying that the content of the listview wasn't notified, yet I have a notification upon updating the data. This is a custom listview adapter. Here is the relevant part of my code: class LoadingThread extends Thread { public void run() { int itemsOriginallyLoaded = 0; synchronized( items ) { itemsOriginallyLoaded = items.size(); } for( int i = itemsOriginallyLoaded ; i < itemsToLoad ; ++i ) { Log.d( LOG_TAG, "Loading item #"+i ); //String item = "FAIL"; //try { String item = "FAIL"; try { item = stockGrabber.getStockString(dataSource.get(i)); } catch (ApiException e) { Log.e(LOG_TAG, "Problem making API request", e); } catch (ParseException e) { Log.e(LOG_TAG, "Problem parsing API request", e); } //} catch (ApiException e) { // Log.e(TAG, "Problem making API request", e); //} catch (ParseException e) { // Log.e(TAG, "Problem parsing API request", e); //} synchronized( items ) { items.add( item ); } itemsLoaded = i+1; uiHandler.post( updateTask ); Log.d( LOG_TAG, "Published item #"+i ); } if( itemsLoaded >= ( dataSource.size() - 1 ) ) allItemsLoaded = true; synchronized( loading ) { loading = Boolean.FALSE; } } } class UIUpdateTask implements Runnable { public void run() { Log.d( LOG_TAG, "Publishing progress" ); notifyDataSetChanged(); } }

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• Compute weighted averages for large numbers

  - by Travis

  I'm trying to get the weighted average of a few numbers. Basically I have: Price - 134.42 Quantity - 15236545 There can be as few as one or two or as many as fifty or sixty pairs of prices and quantities. I need to figure out the weighted average of the price. Basically, the weighted average should give very little weight to pairs like Price - 100000000.00 Quantity - 3 and more to the pair above. The formula I currently have is: ((price)(quantity) + (price)(quantity) + ...)/totalQuantity So far I have this done: double optimalPrice = 0; int totalQuantity = 0; double rolling = 0; System.out.println(rolling); Iterator it = orders.entrySet().iterator(); while(it.hasNext()) { System.out.println("inside"); Map.Entry order = (Map.Entry)it.next(); double price = (Double)order.getKey(); int quantity = (Integer)order.getValue(); System.out.println(price + " " + quantity); rolling += price * quantity; totalQuantity += quantity; System.out.println(rolling); } System.out.println(rolling); return totalQuantity / rolling; The problem is I very quickly max out the "rolling" variable. How can I actually get my weighted average? Thanks!

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• KeyStore, HttpClient, and HTTPS: Can someone explain this code to me?

  - by stormin986

  I'm trying to understand what's going on in this code. KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType()); FileInputStream instream = new FileInputStream(new File("my.keystore")); try { trustStore.load(instream, "nopassword".toCharArray()); } finally { instream.close(); } SSLSocketFactory socketFactory = new SSLSocketFactory(trustStore); Scheme sch = new Scheme("https", socketFactory, 443); httpclient.getConnectionManager().getSchemeRegistry().register(sch); My Questions: trustStore.load(instream, "nopassword".toCharArray()); is doing what exactly? From reading the documentation load() will load KeyStore data from an input stream (which is just an empty file we just created), using some arbitrary "nopassword". Why not just load it with null as the InputStream parameter and an empty string as the password field? And then what is happening when this empty KeyStore is being passed to the SSLSocketFactory constructor? What's the result of such an operation? Or -- is this simply an example where in a real application you would have to actually put a reference to an existing keystore file / password?

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• Is it valid for Hibernate list() to return duplicates?

  - by skaffman

  Is anyone aware of the validity of Hibernate's Criteria.list() and Query.list() methods returning multiple occurrences of the same entity? Occasionally I find when using the Criteria API, that changing the default fetch strategy in my class mapping definition (from "select" to "join") can sometimes affect how many references to the same entity can appear in the resulting output of list(), and I'm unsure whether to treat this as a bug or not. The javadoc does not define it, it simply says "The list of matched query results." (thanks guys). If this is expected and normal behaviour, then I can de-dup the list myself, that's not a problem, but if it's a bug, then I would prefer to avoid it, rather than de-dup the results and try to ignore it. Anyone got any experience of this?

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• Meta Search Engine Architecture

  - by Loki

  The question wasn't clear enough, I think; here's an updated straight to the point question: What are the common architectures used in building a meta search engine and is there any libraries available to build that type of search engine? I'm looking at building an "enterprise" type of search engine where the indexed data could be coming from proprietary (like Autonomy or a Google Box) or public search engines (like Google Web or Yahoo Web).

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• Why aren't arrays expandable?

  - by Mustafa

  When we create an array, we cannot change its size; it's fixed. OK, seems nice, we can create a new bigger array and copy the values one by one and that's little slow. What's the technical background of it?

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• When to use LinkedList<> over ArrayList<>?

  - by sdellysse

  I've always been one to simply use List<String> names = new ArrayList<String>(); I use the interface as the type name for portability, so that when I ask questions such as these I can rework my code. When should LinkedList should be used over ArrayList and vice-versa?

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• Build specific module in multi-module project

  - by Roman

  Hi I have a multi-module project. I thought I can compile only a single module from that multi module project by that line : mvn -amd -pl "module-name" Seems not to work , this command builds only the specific module. Its dependencies are not compiled yet so it fails. Any ideas how to solve that ? Thanks

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• IBM MQ Message Listener

  - by x1a0

  Hi does anyone know how to create a message listener using IBM MQ? I know how to do it using the JMS spec but I am not sure how to do it for IBM MQ. Any links or pointers are greatly appreciated.

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• how to use JComboBox using Enum in Dialog Box

  - by Edan

  Hi, I define enums: enum itemType {First, Second, Third}; public class Item { private itemType enmItemType; ... } How do I use it inside Dialog box using JComboBox? Means, inside the dialog box, the user will have combo box with (First, Second, Third). Also, is it better to use some sort of ID to each numerator? (Integer) thanks.

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• Transactions in hibernate

  - by kumar1425

  Hi I new to hibernate In my project, i need to handle transactions. How to handle declarative transactions with in two classes Examples: //class 1 class A{ createA() { insert(A); } } //class 2 class B { createB() { insert(B); } } //class 3 @Transaction(Exception.class) class C { test() { create(A); create(B); } } As per the above code is there any possibility to handle transactions, in such a way that if the insert in classA success and the insert in the classB fails then the transaction should rollback and remove the record inserted in the table A corresponding to the Class A please help me with this using declarative transactions.... Thanks in adavace....

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• Deploying Multiple Environments in Spring-MVC

  - by jboyd

  Currently all web apps are deployed using seperate config files: <!-- <import bean.... production/> --> <import bean... development/> This has disadvantages, even if you only need to swap out one config file, that I'm sure everyone is familiar with (wondering what just deployed without searching through XML is one of them) I want to add Logging to my application that basically says 'RUNNING IN PRODUCTION MODE', with a description of the services deployed and what mode they are working in. RUNNING IN PRODUCTION MODE Client Service - Production Messaging Service - Local and so on... Is this possible in Spring using a conventional deployment (putting a war on a server)? What other things do people do to manage deployments and software configurations? If not, what other ways could you achieve something similar?

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• A simple two column layout with Swing

  - by Derk

  How to get a sidebar JPanel of a fixed with with Swing. Now I'm trying this: public SidebarPanel() { this.setLayout(new BoxLayout(this, BoxLayout.PAGE_AXIS)); this.setPreferredSize(new Dimension(200, this.getPreferredSize().height)); ... But when I resize the window also the width of the sidebar changes. How to fix this?

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• Jpa subclass mapping

  - by Roy Chan

  I am making a POS like system. I wonder how to map subclass using JPA (this is for my DAO). Product class has product details and OrderProduct class has information about the Product and details about the order. @Entity @Table(name="products") public class Product implements Serializable{ @Id @Column(name="id") @GeneratedValue(strategy = GenerationType.AUTO public int getId(){ return id;} /** Other get/set methods */ } @Entity @Table(name="order_products") public class OrderProduct extends Product{ @Id @Column(name="id") @GeneratedValue(strategy = GenerationType.AUTO) public int getId(){ return id;} /** Other get/set methods */ } I got complain about duplicate @Id. But OrderProduct class really need another id than the product one. How should I map this? DB is something like this Table products id int name varchar(32) Table order_product id int quantity int productid int fk referencing product table Would @IdClass or @AttributeOverride help?

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• @NamedQuery select parameter meaning

  - by sergionni

  Found some examples of @NamedQuery annotations,e.g.: @NamedQuery(name="employeeBySsn" query="select e from Employee e where e.ssn = :ssn") what does parameter e mean? the second usage of it seems like alias name of table and what does "select e" part mean?

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• jaxb entity print out as xml

  - by Cristian Boariu

  Hi, I have a class, let's say User adnotated with @XmlRootElement, with some properties (name, surname etc). I use this class for REST operations, as application/xml. The client will POST User class so i want to keep the values in the log. Is there any method in jax-ws to prints out this object as xml? For instance: log.info("Customers sent a USER"+user.whichMethod()); Customer sent a User <user> <name>cristi</name> <surname>kevin</surname> </user> Thanks.

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• How to perform a non-polymorphic HQL query in Hibernate?

  - by Eli Acherkan

  Hi all, I'm using Hibernate 3.1.1, and in particular, I'm using HQL queries. According to the documentation, Hibernate's queries are polymorphic: A query like: from Cat as cat returns instances not only of Cat, but also of subclasses like DomesticCat. How can I query for instances of Cat, but not of any of its subclasses? I'd like to be able to do it without having to explicitly mention each subclass. I'm aware of the following options, and don't find them satisfactory: Manually filtering the instances after the query, OR: Manually adding a WHERE clause on the discriminator column. It would make sense for Hibernate to allow the user to decide whether a query should be polymorphic or not, but I can't find such an option. Thanks in advance!

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• How to allow for modular development while still running in same JVM?

  - by Marcus

  Our current app runs in a single JVM. We are now splitting up the app into separate logical services where each service runs in its own JVM. The split is being done to allow a single service to be modified and deployed without impacting the entire system. This reduces the need to QA the entire system - just need to QA the interaction with the service being changed. For interservice communication we use a combination of REST, an MQ system bus, and database views. What I don't like about this: REST means we have to marshal data to/from XML DB views couple the systems together which defeats the whole concept of separate services MQ / system bus is added complexity There is inevitably some code duplication between services You have set up n JBoss server configurations, we have to do n number of deployments, n number of set up scripts, etc, etc. Is there a better way to structure an internal application to allow modular development and deployment while allowing the app to run in a single JVM (and achieving the associated benefits)?

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• ArrayList<String> NullPointerException

  - by Carlucho

  Am trying to solve a labyrinth by DFS, using adj List to represent the vertices and edges of the graph. In total there are 12 nodes (3 rows[A,B,C] * 4 cols[0,..,3]). My program starts by saving all the vertex labels (A0,..C3), so far so good, then checks the adjacent nodes, also no problems, if movement is possible, it proceeds to create the edge, here its where al goes wrong. adjList[i].add(vList[j].label); I used the debugger and found that vList[j].label is not null it contains a correct string (ie. "B1"). The only variables which show null are in adjList[i], which leads me to believe i have implemented it wrongly. this is how i did it. public class GraphList { private ArrayList<String>[] adjList; ... public GraphList(int vertexcount) { adjList = (ArrayList<String>[]) new ArrayList[vertexCount]; ... } ... public void addEdge(int i, int j) { adjList[i].add(vList[j].label); //NULLPOINTEREXCEPTION HERE } ... } I will really appreaciate if anyone can point me on the right track regrading to what its going wrong... Thanks!

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• How can a link within a WebView load another layout using javascript?

  - by huffmaster

  So I have 2 layout files (main.xml, featured.xml) and both each have a single WebView. When the application starts "main.xml" loads a html file into it's WebView. In this html file I have a link that calls javascript that runs code in the Activity that loaded the html. Once back in this Activity code though I try running setContentView(R.layout.featured) but it just bombs out on me. If I debug it just dies without any real error and if I run it the application just Force closes. Am I going about this correctly or should I be doing something differently? final private int MAIN = 1; final private int FEATURED = 2; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); webview = (WebView) findViewById(R.id.wvMain); webview.getSettings().setJavaScriptEnabled(true); webview.getSettings().setSupportZoom(false); webview.addJavascriptInterface(new EHJavaScriptInterface(), "eh"); webview.loadUrl("file:///android_asset/default.html"); } final class EHJavaScriptInterface { EHJavaScriptInterface() { } public void loadLayout(final String lo) { int i = Integer.parseInt(lo.trim()); switch (i) { /****** THIS IS WHERE I'M BOMBING OUT *********/ case FEATURED: setContentView(R.layout.featured);break; case MAIN: setContentView(R.layout.main);break; } } }

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• inline images in email using javamail

  - by manu1001

  I want to send an email with an inline image using javamail. I'm doing something like this. MimeMultipart content = new MimeMultipart("related"); BodyPart bodyPart = new MimeBodyPart(); bodyPart.setContent(message, "text/html; charset=ISO-8859-1"); content.addBodyPart(bodyPart); bodyPart = new MimeBodyPart(); DataSource ds = new ByteArrayDataSource(image, "image/jpeg"); bodyPart.setDataHandler(new DataHandler(ds)); bodyPart.setHeader("Content-Type", "image/jpeg; name=image.jpg"); bodyPart.setHeader("Content-ID", "<image>"); bodyPart.setHeader("Content-Disposition", "inline"); content.addBodyPart(bodyPart); msg.setContent(content); I've also tried bodyPart.setHeader("inline; filename=image.jpg"); and bodyPart.setDisposition("inline"); but no matter what, the image is being sent as an attachment and the Content-Dispostion is turning into "attachment". How do I send an image inline in the email using javamail?

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• Are multiply-thrown Exceptions checked or runtime?

  - by froadie

  I have an Exception chain in which method1 throws an Exception to method2 which throws the Exception on to main. For some reason, the compiler forces me to deal with the error in method2 and marks it as an error if I don't, indicating that it's a checked Exception. But when the same Exception is thrown further down the line to main, the compiler allows me to ignore it and doesn't display any errors. The original Exception in method1 is a ParseException, which is checked. But the method has a generic throws Exception clause in the header, and the same object is thrown to method2, which has an identical throws Exception clause. When and how does this Exception lose the status of being checked / caught by the compiler? Edited to clarify: public void method1() throws Exception{ // code that may generate ParseException } public void method2() throws Exception{ method1(); //compiler error } public static void main(String[] args){ method2(); //ignored by compiler }

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• javascript server issue

  - by sarah

  Onchage of selection i am calling a javascript to make a server call using struts1.2 but its not making a call.Please let me know where i am going wrong,below is the code <html:form action="/populate"> <html:select property="tName" onchange="test()">"> <html:option value="">SELECT</html:option> <html:options name="tList" /> </html:select> </html:form> and stuts-config has <action path="/populate" name="tForm" type="com.testAction" validate="false" parameter="method" scope="request" > <forward name="success" path="/failure.jsp" /> </action> and javascript is function test(){ var selObj = document.getElementById("tName"); var selIndex = selObj.selectedIndex; if (selIndex != 0) { document.form[0].selIndex.action="/populate.do?method=execute&testing="+selIndex; document.form[0].submit(); } }

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