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  • Testing a quadratic equation

    - by user1201587
    I'm doing a code testing for a program that calculate the results for a quadratic equation I need to have test data for the following situation, when a is not zero and d positive there is two possibilities which are in the code below, I need to find an example for the first satiation when Math.abs(b / a - 200.0) < 1.0e-4 , all the values that I have tried, excute the second one caption= "Two roots"; if (Math.abs(b / a - 200.0) < 1.0e-4) { System.out.println("first one"); x1 = (-100.0 * (1.0 + Math.sqrt(1.0 - 1.0 / (10000.0 * a)))); x2 = (-100.0 * (1.0 - Math.sqrt(1.0 - 1.0 / (10000.0 * a)))); } else { System.out.println("secrst one"); x1 = (-b - Math.sqrt(d)) / (2.0 * a); x2 = (-b + Math.sqrt(d)) / (2.0 * a); } } }

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  • How can I force the server socket to re-accept a request from a client?

    - by Roman
    For those who does not want to read a long question here is a short version: A server has an opened socket for a client. The server gets a request to open a socket from the same client-IP and client-port. I want to fore the server not to refuse such a request but to close the old socket and open a new one. How can I do ti? And here is a long (original) question: I have the following situation. There is an established connection between a server and client. Then an external software (Bonjour) says to my client the it does not see the server in the local network. Well, client does nothing about that because of the following reasons: If Bonjour does not see the server it does not necessarily means that client cannot see the server. Even if the client trusts the Bonjour and close the socket it does not improve the situation ("to have no open socket" is worser that "to have a potentially bad socket"). So, client do nothing if server becomes invisible to Bonjour. But than the server re-appears in the Bonjour and Bonjour notify the client about that. In this situation the following situations are possible: The server reappears on a new IP address. So, the client needs to open a new socket to be able to communicate with the server. The server reappears on the old IP address. In this case we have two subcases: 2.1. The server was restarted (switched off and then switched on). So, it does not remember the old socket (which is still used by the client). So, client needs to close the old socket and open a new one (on the same server-IP address and the same server-port). 2.2. We had a temporal network problem and the server was running the whole time. So, the old socket is still available for the use. In this case the client does not really need to close the old socket and reopen a new one. But to simplify my life I decide to close and reopen the socket on the client side in any case (in spite on the fact that it is not really needed in the last described situation). But I can have problems with that solution. If I close the socket on the client side and than try to reopen a socket from the same client-IP and client-port, server will not accept the call for a new socket. The server will think that such a socket already exists. Can I write the server in such a way, that it does not refuse such calls. For example, if it (the server) sees that a client send a request for a socket from the same client-IP and client-port, it (server) close the available socket, associated with this client-IP and client-port and than it reopens a new socket.

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  • PreparedStatement and setTimestamp in oracle jdbc

    - by Roman
    Hi everyone, I am using PreparedStatement with Timestamp in where clause: PreparedStatement s=c.prepareStatement("select utctimestamp from t where utctimestamp>=? and utctimestamp<?"); s.setTimestamp(1, new Timestamp(1273017600000L)); //2010-05-05 00:00 GMT s.setTimestamp(2, new Timestamp(1273104000000L)); //2010-05-06 00:00 GMT The result I get is different, when I have different time zones on the client computer. Is this a bug in Oracle jdbc? or correct behavior? The parameter is Timestamp, and I expected that no time conversions will be done on the way. The database column type is DATE, but I also checked it with TIMESTAMP column type with the same results. Is there a way to achieve correct result? I cannot change default timezone in the the whole application to UTC. Thanks for your help

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  • Error when deploying site of a maven multi module project with FTP

    - by julien
    I have a multi module project. When I launch mvn site:deploy, the deployment of the base module works fine, but it fails to create the directory of the module sites on the FTP server: [INFO] Error uploading site Embedded error: Required directory: '/myremoteftprepository/myproject-mymodule' is missing When I create the missing directory by hand, it works fine, but I would like to avoid that. It is surprising that the deploy command do not create it. Do you how to force this directory creation? Is it a bug in the wagon-ftp plugin? FYI, here is my POM: <build> <extensions> <!-- Enabling the use of FTP --> <extension> <groupId>org.apache.maven.wagon</groupId> <artifactId>wagon-ftp</artifactId> <version>1.0</version> </extension> </extensions> </build> I have chosen to include the javadoc with: <reporting> <plugins> <!-- include javadoc in the site --> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-javadoc-plugin</artifactId> <version>2.8</version> <configuration> <show>public</show> </configuration> </plugin> </plugins> </reporting> and <distributionManagement> <site> <id>site</id> <name>maven site</name> <url>ftp://ftp.blabla.org/myremoteftprepository</url> </site> </distributionManagement> and my settings.xml is good.

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  • Batch processing JDBC

    - by Wai Hein
    I am practicing JDBC batch processing and having errors: error 1: Unsupported feature error 2: Execute cannot be empty or null Property files include: itemsdao.updateBookName = Update Books set bookname = ? where books.id = ? itemsdao.updateAuthorName = Update books set authorname = ? where books.id = ? I know I can execute about DML statements in one update, but I am practicing batch processing in JDBC. Below is my method public void update(Item item) { String query = null; try { connection = DbConnector.getConnection(); property = SqlPropertiesLoader.getProperties("dml.properties"); connection.setAutoCommit(false); if ( property == null ) { Logging.log.debug("dml.properties does not exist. Check property loader or file name is spelled right"); return; } query = property.getProperty("itemsdao.updateBookName"); statement = connection.prepareStatement(query); statement.setString(1, item.getBookName()); statement.setInt(2, item.getId()); statement.addBatch(query); query = property.getProperty("itemsdao.updateAuthorName"); statement = connection.prepareStatement(query); statement.setString(1, item.getAuthorName()); statement.setInt(2, item.getId()); statement.addBatch(query); statement.executeBatch(); connection.commit(); }catch (ClassNotFoundException e) { Logging.log.error("Connection class does not exist", e); } catch (SQLException e) { Logging.log.error("Violating PK constraint",e); } //helper class th finally { DbUtil.close(connection); DbUtil.closePreparedStatement(statement); }

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  • schedule task with spring mvc

    - by user3586352
    I want to run the following method every specific time in spring mvc project it works fine and print first output but it doesn't access the database so it doesn't display list the method public class ScheduleService { @Autowired private UserDetailService userDetailService; public void performService() throws IOException { System.out.println("first output"); List<UserDetail> list=userDetailService.getAll(); System.out.println(list); } config file <!-- Spring's scheduling support --> <task:scheduled-tasks scheduler="taskScheduler"> <task:scheduled ref="ScheduleService" method="performService" fixed-delay="2000"/> </task:scheduled-tasks> <!-- The bean that does the actual work --> <bean id="ScheduleService" class="com.ctbllc.ctb.scheduling.ScheduleService" /> <!-- Defines a ThreadPoolTaskScheduler instance with configurable pool size. --> <task:scheduler id="taskScheduler" pool-size="1"/>

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  • db2 jdbc driver does not release table locks

    - by as
    situation: We have a web service running on tomcat accessing DB2 database on AS400, we are using JTOPEN drivers for JNDI connections handled by tomcat. For handling transactions and access to database we are using Spring. For each select system takes JDBC connection from JNDI (i.e. from connection pool), does selection, and in the end it closes ResultSet, Statement and releases Connection in that order. That passes fine, shared lock on table dissappears. When we want to do update the same way as we did with select (exception on ResultSet object, we don't have one in such situation), after releasing Connection to JNDI lock on table stays. If we put maxIdle=0 for number of connections in JNDI configuration, this problem disappears, but this degrades performances, we have cca 100 users online on that service, we need few connections to be alive in pool. What do you suggest?

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  • Can JAXB store the class name in the XML so that the the deserialize code doesn't need knowledge of the class?

    - by Andrew
    It seems the standard approach for deserializing JAXB XML is to specify the package name when creating the context. Then, JAXB looks up the class based on the root element: JAXBContext jc = JAXBContext.newInstance("com.foo"); Unmarshaller u = jc.createUnmarshaller(); Object o = u.unmarshal(new StringReader("...")); I'm looking for a more flexible approach where I don't have to specify the package name and could still deserialize any object. This would be as simple as JAXB storing the package in the XML, but I can't seem to find out how to do this. I can write the code to do it myself but that would be unpleasant. It would like JAXB to do it, if possible. BTW, I am not using schemas, just Annotations and marshal/unmarshal. Any ideas?

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  • Refactoring a long method that simply populates

    - by Jeune
    I am refactoring a method which is over 500 lines (don't ask me why) The method basically queries a list of maps from the database and for each map in the list does some computation and adds the value of that computation to the map. There are however too many computations and puts being done that the code has reached over 500 lines already! Here's a sample preview: public List<Hashmap> getProductData(...) { List<Hashmap> products = productsDao.getProductData(...); for (Product product: products) { product.put("Volume",new BigDecimanl(product.get("Height")* product.get("Width")*product.get("Length")); if (some condition here) { //20 lines worth of product.put(..,..) } else { //20 lines worth of product.put(..,..) } //3 more if-else statements like the one above try { product.put(..,..) } catch (Exception e) { product.put("",..) } //over 8 more try-catches of the form above } Any ideas on how to go about refactoring this?

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  • Can fields of the class and arguments of the method interfere?

    - by Roman
    I have a class with a fields called "a". In the class I have a method and in the list of arguments of this method I also have "a". So, which "a" I will see inside of the method? Will it be the field or it will be the argument of the method? public class myClass { private String a; // Method which sets the value of the field "a". public void setA(String a) { a = a; } } By the way, there is a similar situation. A method has some local (for method) variables whose names coincide with the names of the fields. What will the "see" the method if I refer to such a method-local variable inside the method (the field or the local variable)?

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  • Using a custom annotation on a Spring MVC controller method from an interceptor.

    - by Speck
    I have a custom annotation with which I've annotated a method in my Controller alongside a @ReqestMapping. The goal is to use the values set in the custom annotation from a HandlerInterceptor to perform a task. I have the interceptor (HandlerInterceptorAdaptor) mapped and it executes. If I set a breakpoint in my concrete Interceptor I can inspect the HttpServletRequest, HttpServletResponse, and handler Objects. However, I cannot see how to 1, obtain the method which the request is trying to access 2, obtain the Annotations on that method and 3, of course, obtain the values set by the annotation. Can anyone point me to good documentation for this? Please and Thank You.

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  • switch statemt functioning improperly and giving error when i put break;

    - by nav
    The following is the code i used in a program - over here the month variable is an integer switch(month) { case 1: case 3: case 5: case 7: case 8: case 10: case 12: return 31; break; case 2: return 28; break; case 4: case 6: case 9: case 11: return 30; break; default: System.out.println("Invalid month."); return 0; } surprisingly, when i use the above switch construct.. it gives an error saying.. code unreachable for statements after each break statement Then i removed all the break statements, and the new code looks like this --- switch(month) { case 1: case 3: case 5: case 7: case 8: case 10: case 12: return 31; case 2: return 28; case 4: case 6: case 9: case 11: return 30; default: System.out.println("Invalid month."); return 0; } Now.. after removing the break statements .. the code worked perfectly well.. My question is... in the switch construct.. it is mandatory to use break.. or else the control flow continued.. and all the conditions are tested and executed!! right??? So why in the world is the previous ** syntactically Right** version giving an error.. and the modified syntactically incorrect version running perfectly well.. Any explanation.. anyone!!

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  • RMI client tracking

    - by 0000
    I'm building a Client / Server app that has some very specific needs. There are 2 kinds of servers: the first kind provide most of the remote procedures and clients connect to these directly, while the second kind is a single server that should keep track of what users are active (clients) and how many servers of the first kind are active when a method is called. The main thing is that the monitor should ONLY connect to the servers and not the clients directly. My first idea was to implement a simple login/logout rmi method when a client connects/ disconnects and keep track of those in a list but the main problem is when a client or server end abnormally. For example, if a client goes offline abruptly the server should somehow be notified and update the list accordingly, while if a server goes out all of the clients connected to it should be marked as not active in the control server. Any ideas of how to implement this functionality would be appreciated.

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  • What is the fastest findByName query with hibernate?

    - by Karussell
    I am sure I can improve the performance of the following findByName query of hibernate: public List<User> findByName(String name) { session.createCriteria(User.class).add(Restrictions.eq("name", name)).list(); } In which way should I improve it or even more important: in which ways should I improve it first? I will need the full object with all the collections (layz or not) and deps of this class.

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  • Oval collision detection not working properly

    - by William
    So I'm trying to implement a test where a oval can connect with a circle, but it's not working. edist = (float) Math.sqrt(Math.pow((px + ((pwidth/2) )) - (bx + (bsize/2)), 2) + Math.pow(-((py + ((pwidth/2)) ) - (bx + (bsize/2))), 2)); and here is the full code (requires Slick2D): import org.newdawn.slick.AppGameContainer; import org.newdawn.slick.BasicGame; import org.newdawn.slick.Color; import org.newdawn.slick.GameContainer; import org.newdawn.slick.Graphics; import org.newdawn.slick.Input; import org.newdawn.slick.SlickException; public class ColTest extends BasicGame{ float px = 50; float py = 50; float pheight = 50; float pwidth = 50; float bx = 200; float by = 200; float bsize = 200; float edist; float pspeed = 3; Input input; public ColTest() { super("ColTest"); } @Override public void init(GameContainer gc) throws SlickException { } @Override public void update(GameContainer gc, int delta) throws SlickException { input = gc.getInput(); try{ if(input.isKeyDown(Input.KEY_UP)) py-=pspeed; if(input.isKeyDown(Input.KEY_DOWN)) py+=pspeed; if(input.isKeyDown(Input.KEY_LEFT)) px-=pspeed; if(input.isKeyDown(Input.KEY_RIGHT)) px+=pspeed; } catch(Exception e){} } public void render(GameContainer gc, Graphics g) throws SlickException { g.setColor(new Color(255,255,255)); g.drawString("col: " + col(), 10, 10); g.drawString("edist: " + edist + " dist: " + dist, 10, 100); g.fillRect(px, py, pwidth, pheight); g.setColor(new Color(255,0,255)); g.fillOval(px, py, pwidth, pheight); g.setColor(new Color(255,255,255)); g.fillOval(200, 200, 200, 200); } public boolean col(){ edist = (float) Math.sqrt(Math.pow((px + ((pwidth/2) )) - (bx + (bsize/2)), 2) + Math.pow(-((py + ((pwidth/2)) ) - (bx + (bsize/2))), 2)); if(edist <= (bsize/2) + (px + (pwidth/2))) return true; else return false; } public float rotate(float x, float y, float ox, float oy, float a, boolean b) { float dst = (float) Math.sqrt(Math.pow(x-ox,2.0)+ Math.pow(y-oy,2.0)); float oa = (float) Math.atan2(y-oy,x-ox); if(b) return (float) Math.cos(oa + Math.toRadians(a))*dst+ox; else return (float) Math.sin(oa + Math.toRadians(a))*dst+oy; } public static void main(String[] args) throws SlickException { AppGameContainer app = new AppGameContainer( new ColTest() ); app.setShowFPS(false); app.setAlwaysRender(true); app.setTargetFrameRate(60); app.setDisplayMode(800, 600, false); app.start(); } }

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  • Find the class of the generic object

    - by Mgccl
    Suppose I have the following class. public class gen<T> { public gen(){ } Class<T> class(){ //something that figures out what T is. } } How can I implement the class() function without pass any additional information? What I did is here, but I have to pass a object of T into the object gen. public class gen<T> { public gen(){ } Class<T> class(T var){ return (Class<T>) var.getClass(); } }

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  • What is the effect of final variable declaration in methods?

    - by Finbarr
    Classic example of a simple server: class ThreadPerTaskSocketServer { public static void main(String[] args) throws IOException { ServerSocket socket = new ServerSocket(80); while (true) { final Socket connection = socket.accept(); Runnable task = new Runnable() { public void run() { handleRequest(connection); } }; new Thread(task).start(); } } } Why should the Socket be declared as final? Is it because the new Thread that handles the request could refer back to the socket variable in the method and cause some sort of ConcurrentModificationException?

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  • Getting the right result of mouse click event

    - by Jessy
    Hello, I'm curious why I got the "right" BUT "wrong"number of result when I click the mouse. I supposed to print on the console mouseClicked once everytimes the mouse is clicked. However I got many of them printed out everytimes I clicked the mouse ...sometimes 5 e.g. mouseClicked mouseClicked mouseClicked mouseClicked mouseClicked Instead of just mouseClicked Why? public void mouseClicked(MouseEvent arg0) { System.out.println("mouseClicked"); }

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