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  • Find location using only distance and range?

    - by pinnacler
    Triangulation works by checking your angle to three KNOWN targets. "I know the that's the Lighthouse of Alexandria, it's located here (X,Y) on a map, and it's to my right at 90 degrees." Repeat 2 more times for different targets and angles. Trilateration works by checking your distance from three KNOWN targets. "I know the that's the Lighthouse of Alexandria, it's located here (X,Y) on a map, and I'm 100 meters away from that." Repeat 2 more times for different targets and ranges. But both of those methods rely on knowing WHAT you're looking at. Say you're in a forest and you can't differentiate between trees, but you know where key trees are. These trees have been hand picked as "landmarks." You have a robot moving through that forest slowly. Do you know of any ways to determine location based solely off of angle and range, exploiting geometry between landmarks? Note, you will see other trees as well, so you won't know which trees are key trees. Ignore the fact that a target may be occluded. Our pre-algorithm takes care of that. 1) If this exists, what's it called? I can't find anything. 2) What do you think the odds are of having two identical location 'hits?' I imagine it's fairly rare. 3) If there are two identical location 'hits,' how can I determine my exact location after I move the robot next. (I assume the chances of having 2 occurrences of EXACT angles in a row, after I reposition the robot, would be statistically impossible, barring a forest growing in rows like corn). Would I just calculate the position again and hope for the best? Or would I somehow incorporate my previous position estimate into my next guess? If this exists, I'd like to read about it, and if not, develop it as a side project. I just don't have time to reinvent the wheel right now, nor have the time to implement this from scratch. So if it doesn't exist, I'll have to figure out another way to localize the robot since that's not the aim of this research, if it does, lets hope it's semi-easy.

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  • Overwrite HTTP method with JAX-RS

    - by deamon
    Today's browsers (or HTML < 5) only support HTTP GET and POST, but to communicate RESTful one need PUT and DELETE too. If the workaround should not be to use Ajax, something like a hidden form field is required to overwrite the actual HTTP method. Rails uses the following trick: <input name="_method" type="hidden" value="put" /> Is there a possibility to do something similar with JAX-RS?

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  • Counting the number of visitors for a web page - JavaScript and Struts

    - by Dj
    Hi i am Dhananjay, I need to keep track of the number of visitors to a web page. I have planned like this: on load of the home page, I will call a javascript callCounter(); From javascript, I need then to call an action and update a record in database. Please help me with this. How do i call the action? I should be in the same home jsp after updating database. Thanks in advance, Dhananjay

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  • Invoke a subclass method of an anonymous class

    - by arjacsoh
    I am trying right now to dig into anonymous classes and one question was just arised I 'd prefer not to refer to much details and to pose my question straightforward: How can I invoke the method sizzle() in the following anonymous class: public class Popcorn { public void pop() { System.out.println("popcorn"); } } class Food { Popcorn p = new Popcorn() { public void sizzle() { System.out.println("anonymous sizzling popcorn"); } public void pop() { System.out.println("anonymous popcorn"); } }; public void popIt() { p.pop(); // OK, Popcorn has a pop() method p.sizzle(); // Not Legal! Popcorn does not have sizzle() } } It is known and definite in polymorphism rules that a refernce of a superclass cannot invoke methods of subclass without downcasting (even if it refers to an object of the given subclass). However in the above case what is the "key" to invoke the sizzle() method?

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  • How do I share a Hibernate SessionFactory across web applications?

    - by Jer
    I have two web applications that are running on a single Tomcat server and are connected to the same database with Hibernate. I am concerned that having two SessionFactory instances running around might cause some issues. Also, since both web applications share much of the same application logic, I thought it would be a good idea to centralize as much as I could. And since I use Spring for DI and Hibernate configuration it would make sense to have a single ApplicationContext as well. How would I go about doing something like this? Do I need to deploy a headless WAR that creates an ApplicationContext and thus a SessionFactory and allow each application access to it? Is this even a good idea?

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  • Where did this class come from?

    - by Karl
    How would you go about establishing where a class ( or maybe resource ) has been loaded from? I am trying to work out exactly where a class has been loaded from. Does anyone know if you can find out the following: Which Jar file did the class come from ? What classloader loaded the file?

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  • How can I pass a dynamic backing bean into a JSF 2.0 page using facelets?

    - by kgrad
    Hi, I am using a JSF 2.0 to create a web app (purely jee6, without spring/seam etc.). I would like to have a single xhtml page but pass the proper backing bean / entity into it. For example, I would like to be able to edit a user other than the logged in user, I have a user edit page which displays the information of the logged in user (being tracked by my session), I would like to instead pass in a user selected from a list and edit that user's information, without switching the user that is stored in the session or creating a separate xhtml page (violating DRY). The "best" way I can see to achieve this would be to reuse the exact same xhtml page that I am using to display the logged-in-user's edit page, but simply pass in a different entity in some way. Perhaps calling the setter in the backing bean before redirecting to the page (if this is even possible) or some other solution that does not violate DRY. Perhaps I have designed this all wrong, is there a way to pass in entities to JSF pages? thanks.

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  • log4j properties file: how to configure ?

    - by EugeneP
    Is it right that the procedure of using log4j looks like this: 1) put a .properties file somewhere in a project folder 2) in an initialization method, that runs only once, invoke PropertyConfigurator.configure("path_to_file"); 3) in every method we need to use logger we define a static logger variable and simply invoke getLogger(class) I'm asking you this: what if the initialization module is not defined? Where to put "log4j.properties" file so that we wouldn't need to invoke propertyconfigurator.configure at all, or if it's not possible, is it ok to invoke PropertyConfigurator.configure("path_to_file") in every method that uses a logger?

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  • Layout of Ant build.xml with junit tests

    - by Derk
    In a project I have a folder src for all application source code and a different folder test for all junit test (both with a simular package hierarchy). Now I want that Ant can run all tests in in test folder, bot the problem is that now also files in the src folder with "Test" in the filename are included. This is the test target in the build.xml: <target name="test" depends="build"> <mkdir dir="reports/tests" /> <junit fork="yes" printsummary="yes"> <formatter type="xml"/> <classpath> <path location="${build}/WEB-INF/classes"/> <fileset dir="${projectname.home}/lib"> <include name="servlet-api.jar"/> <include name="httpunit.jar"/> <include name="Tidy.jar"/> <include name="js.jar"/> <include name="junit.jar"/> </fileset> </classpath> <batchtest todir="reports/tests"> <fileset dir="${build}/WEB-INF/classes"> <include name="**/*Test.class"/> </fileset> </batchtest> </junit> And I have added the test folder to the build target: <target name="build" depends="init,init-props,prepare"> <javac source="1.5" debug="true" destdir="${build}/WEB-INF/classes"> <src path="src" /> <src path="test" /> <classpath refid="classpath"/> </javac> </target>

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  • How does this code break the Law of Demeter?

    - by Dave Jarvis
    The following code breaks the Law of Demeter: public class Student extends Person { private Grades grades; public Student() { } /** Must never return null; throw an appropriately named exception, instead. */ private synchronized Grades getGrades() throws GradesException { if( this.grades == null ) { this.grades = createGrades(); } return this.grades; } /** Create a new instance of grades for this student. */ protected Grades createGrades() throws GradesException { // Reads the grades from the database, if needed. // return new Grades(); } /** Answers if this student was graded by a teacher with the given name. */ public boolean isTeacher( int year, String name ) throws GradesException, TeacherException { // The method only knows about Teacher instances. // return getTeacher( year ).nameEquals( name ); } private Grades getGradesForYear( int year ) throws GradesException { // The method only knows about Grades instances. // return getGrades().getForYear( year ); } private Teacher getTeacher( int year ) throws GradesException, TeacherException { // This method knows about Grades and Teacher instances. A mistake? // return getGradesForYear( year ).getTeacher(); } } public class Teacher extends Person { public Teacher() { } /** * This method will take into consideration first name, * last name, middle initial, case sensitivity, and * eventually it could answer true to wild cards and * regular expressions. */ public boolean nameEquals( String name ) { return getName().equalsIgnoreCase( name ); } /** Never returns null. */ private synchronized String getName() { if( this.name == null ) { this.name == ""; } return this.name; } } Questions How is the LoD broken? Where is the code breaking the LoD? How should the code be written to uphold the LoD?

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  • JNDI InvalidnameException for CN 'LastName, FirstName'

    - by user321524
    Hi: I am writing to active directory using JNDI, it is successful for "CN=Yuri Gagarin,OU=Admins,DC=ead,DC=ubc,DC=ca"; but fails for "CN=Gagarin, Yuri,OU=Admins,DC=ead,DC=ubc,DC=ca". I need to store displayName, cn, name in the format 'lastName, FirstName'. What do I need to do to get this going? Thanks very much.

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  • The fastest way to do a collection subtraction

    - by Tony
    I have two Sets. Set<B> b is the subset of Set<A> a. they're both very huge Sets. I want to subtract b from a , what's the best practice to do this common operation ? I've written to many codes like this , and I don't think it's efficient. what's your idea ? for(int i = 0 ; i < a.size(); i++) { for (int j=0 ; j < b.size() ;j++) { // do comparison , if found equals ,remove from a break; } } And I want to find an algorithm , not only applies to Sets, also works for Array.

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  • Passing empty list as parameter to JPA query throws error

    - by Tuukka Mustonen
    If I pass an empty list into a JPA query, I get an error. For example: List<Municipality> municipalities = myDao.findAll(); // returns empty list em.createQuery("SELECT p FROM Profile p JOIN p.municipality m WHERE m IN (:municipalities)") .setParameter("municipalities", municipalities) .getResultList(); Because the list is empty, Hibernate generates this in SQL as "IN ()", which gives me error with Hypersonic database. There is a ticket for this in Hibernate issue tracking but there are not many comments/activity there. I don't know about support in other ORM products or in JPA spec either. I don't like the idea of having to manually check for null objects and empty lists every time. Is there some commonly known approach/extension to this? How do you handle these situations?

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  • Why a "private static" is not seen in a method?

    - by Roman
    I have a class with the following declaration of the fields: public class Game { private static String outputFileName; .... } I set the value of the outputFileName in the main method of the class. I also have a write method in the class which use the outputFileName. I always call write after main sets value for outputFileName. But write still does not see the value of the outputFileName. It say that it's equal to null. Could anybody, pleas, tell me what I am doing wrong? ADDED As it is requested I post more code: In the main: String outputFileName = userName + "_" + year + "_" + month + "_" + day + "_" + hour + "_" + minute + "_" + second + "_" + millis + ".txt"; f=new File(outputFileName); if(!f.exists()){ try { f.createNewFile(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } System.out.println("IN THE MAIN!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"); System.out.println("------>" + outputFileName + "<------"); This line outputs me the name of the file. Than in the write I have: public static void write(String output) { // Open a file for appending. System.out.println("==========>" + outputFileName + "<============"); ...... } And it outputs null.

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  • AutoCompleteTextView showing suggestions only for the first word entered

    - by DixieFlatline
    Hello! My autocompletetextview shows suggestions only for the first entered word. So if i write "ki" suggestions for king will popup. But if i enter "queen whitespace ki" there will be no suggestion for king. textView = (AutoCompleteTextView) findViewById(R.id.predlogi); String[] pred = getResources().getStringArray(R.array.predlogi); ArrayAdapter adapter = new ArrayAdapter<String>(this, android.R.layout.simple_dropdown_item_1line, pred); textView.setAdapter(adapter); textView.setThreshold(2); Is there any property that should be set to textView?

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  • Sorting a text file by date - Date looks like DD/MM/YYYY

    - by John N
    I am trying to sort the dates from the earliest to the latest. I was thinking about using the bufferedreader and do a try searching the first 2 characters of the string and then the 4th and 5th characters and finally the 7th and 8th characters, ignoring the slashes. The following is an example of the text file I have: 04/24/2010 - 2000.0 (Deposit) 09/05/2010 - 20.0 (Fees) 02/30/2007 - 600.0 (Deposit) 06/15/2009 - 200.0 (Fees) 08/23/2010 - 300.0 (Deposit) 06/05/2006 - 500.0 (Fees)

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  • How this is code is getting compiled even though we are using a constant which is defined later?

    - by GK
    In the following code DEFAULT_CACHE_SIZE is declared later, but it is used to assign a value to String variable before than that, so was curious how is it possible? public class Test { public String getName() { return this.name; } public int getCacheSize() { return this.cacheSize; } public synchronized void setCacheSize(int size) { this.cacheSize = size; System.out.println("Cache size now " + this.cacheSize); } private final String name = "Reginald"; private int cacheSize = DEFAULT_CACHE_SIZE; private static final int DEFAULT_CACHE_SIZE = 200; }

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  • Servlet requests are executed sequentially for no apparent reason in Glassfish v3

    - by Fabien Benoit
    Hi, I'm using Glassfish 3 Web profile and can't get http workers to execute concurrently requests on a servlet. This is how i observed the problem. I've made a very simple servlet, that writes the current thread name to the standard output and sleep for 10 seconds : protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println(Thread.currentThread().getName()); try { Thread.sleep(10000); // 10 sec } catch (InterruptedException ex) {} } } And when i'm running several simultaneous requests, I clearly see in the logs that the requests are sequentially executed (one trace every 10 seconds). INFO: http-thread-pool-8080-(2) (10 seconds later...) INFO: http-thread-pool-8080-(1) (10 seconds later...) INFO: http-thread-pool-8080-(2) etc. All my GF settings are untouched - it's the out-of-the-box config (the default thread pool is 2 threads min, 5 max if I recall properly). ...I really don't understand why the sleep() block all the others worker threads. Any insight would be greatly appreciated ! Thanks, Fabien

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  • Where to put default-servlet-handler in Spring MVC configuration

    - by gigadot
    In my web.xml, the default servlet mapping, i.e. /, is mapped to Spring dispatcher. In my Spring dispatcher configuration, I have DefaultAnnotationHandlerMapping, ControllerClassNameHandlerMapping and AnnotationMethodHandlerAdapter which allows me to map url to controllers either by its class name or its @Requestmapping annotation. However, there are some static resources under the web root which I also want spring dispatcher to serve using default servlet. According to Spring documentation, this can be done using <mvc:default-servlet-handler/> tag. In the configuration below, there are 4 candidate locations that I marked which are possible to insert this tag. Inserting the tag in different location causes the dispatcher to behave differently as following : Case 1 : If I insert it at location 1, the dispatcher will no longer be able to handle mapping by the @RequestMapping and controller class name but it will be serving the static content normally. Cas 2, 3 : It will be able to handle mapping by the @RequestMapping and controller class name as well as serving the static content if other mapping cannot be done successfully. Case 4 : It will not be able to serve the static contents. Therefore, Case 2 and 3 are desirable .According to Spring documentation, this tag configures a handler which precedence order is given to lowest so why the position matters? and Which is the best position to put this tag? <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd"> <context:annotation-config/> <context:component-scan base-package="webapp.controller"/> <!-- Location 1 --> <!-- Enable annotation-based controllers using @Controller annotations --> <bean id="annotationUrlMapping" class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping"/> <!-- Location 2 --> <bean id="controllerClassNameHandlerMapping" class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping"/> <!-- Location 3 --> <bean id="annotationMethodHandlerAdapter" class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter"/> <!-- Location 4 --> <mvc:default-servlet-handler/> <!-- All views are JSPs loaded from /WEB-INF/jsp --> <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/> <property name="prefix" value="/WEB-INF/jsp/"/> <property name="suffix" value=".jsp"/> </bean> </beans>

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  • Creating JTable Row Header

    - by Chandu
    Hi all, I'm new to JTable.I'm working in Swings using JTable & Toplink(JPA). I have two buttons "add Row", "Del Row" and I have some records displayed from db. when ever "add row" is clicked a new record, row header should be added to JTable with an auto increment number displayed in sequential order to the JTable Row Header. During deletion using "Del row " button the record has to be deleted & not its corresponding header so that next rows got updated to the previous headers & the auto increment number remain unchanged and always be in sequence. please help me on this regard. Thanks in advance, Chandu

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  • JPA @ManyToMany on only one side?

    - by Ethan Leroy
    I am trying to refresh the @ManyToMany relation but it gets cleared instead... My Project class looks like this: @Entity public class Project { ... @ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER) @JoinTable(name = "PROJECT_USER", joinColumns = @JoinColumn(name = "PROJECT_ID", referencedColumnName = "ID"), inverseJoinColumns = @JoinColumn(name = "USER_ID", referencedColumnName = "ID")) private Collection<User> users; ... } But I don't have - and I don't want - the collection of Projects in the User entity. When I look at the generated database tables, they look good. They contain all columns and constraints (primary/foreign keys). But when I persist a Project that has a list of Users (and the users are still in the database), the mapping table doesn't get updated gets updated but when I refresh the project afterwards, the list of Users is cleared. For better understanding: Project project = ...; // new project with users that are available in the db System.out.println(project getUsers().size()); // prints 5 em.persist(project); System.out.println(project getUsers().size()); // prints 5 em.refresh(project); System.out.println(project getUsers().size()); // prints 0 So, how can I refresh the relation between User and Project?

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