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  • Is this an example of polymorphism?

    - by computer-science-student
    I'm working on a homework assignment (a project), for which one criterion is that I must make use of polymorphism in a way which noticeably improves the overall quality or functionality of my code. I made a Hash Table which looks like this: public class HashTable<E extends Hashable>{ ... } where Hashable is an interface I made that has a hash() function. I know that using generics this way improves the quality of my code, since now HashTable can work with pretty much any type I want (instead of just ints or Strings for example). But I'm not sure if it demonstrates polymorphism. I think it does, because E can be any type that implements Hashable. In other words HashTable is a class which can work with (practically) any type. But I'm not quite sure - is that polymorphism? Perhaps can I get some clarification as to what exactly polymorphism is? Thanks in advance!

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  • Do Blob properties on entities affect query performance?

    - by Jaroslav Záruba
    Hello I'm trying to make my mind on whether to store a binary representation of an entity as its Blob property, or whether I better keep the blobs in some separate 'wrapping' class. Possible impact on memory heap and/or a query execution time are my concerns in the first case, complexity votes against the other one. I know Blobs are not indexed, i.e. index size is not what I'm worrying about. Also I assume for blobs Datastore puts defaultFetchGroup to false, but does it mean that blobs don't make a difference in queries? Regards J. Záruba

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  • How to find the first declaring method for a reference method

    - by Oliver Gierke
    Suppose you have a generic interface and an implementation: public interface MyInterface<T> { void foo(T param); } public class MyImplementation<T> implements MyInterface<T> { void foo(T param) { } } These two types are frework types. In the next step I want allow users to extend that interface as well as redeclare foo(T param) to maybe equip it with further annotations. public interface MyExtendedInterface extends MyInterface<Bar> { @Override void foo(Bar param); // Further declared methods } I create an AOP proxy for the extended interface and intercept especially the calls to furtherly declared methods. As foo(…) is no redeclared in MyExtendedInterface I cannot execute it by simply invoking MethodInvocation.proceed() as the instance of MyImplementation only implements MyInterface.foo(…) and not MyExtendedInterface.foo(…). So is there a way to get access to the method that declared a method initially? Regarding this example is there a way to find out that foo(Bar param) was declared in MyInterface originally and get access to the accoriding Method instance? I already tried to scan base class methods to match by name and parameter types but that doesn't work out as generics pop in and MyImplementation.getMethod("foo", Bar.class) obviously throws a NoSuchMethodException. I already know that MyExtendedInterface types MyInterface to Bar. So If I could create some kind of "typed view" on MyImplementation my math algorithm could work out actually.

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  • How to get login password in servlets

    - by Dusk
    I've successfully implemented form based authentication, and now I want to get the username and password to initialize session object in javamail from servlets. How can I do that? I can getlogin username by using method request.getRemoteUser(), but I don't know how to get the password. If I create any session object like: authentication = new PasswordAuthentication(user,password); Properties props = new Properties(); props.put("mail.host", "localhost"); props.put("mail.debug",true); props.put("mail.store.protocol", "pop3"); props.put("mail.transport.protocol", "smtp"); Session session = Session.getInstance(props, this); then how can I get inbox messages from mail server based upon particular username and password, if I don't pass any password from servlets to PasswordAuthentication object?

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  • Stop MediaScanner scanning of certain directory

    - by kape123
    Is there a way to notify MediaScanner service on Android platform not to scan certain directories? I have application that encrypts images on SD card and after I do that MediaScanner goes wild in LogCat (writing out "not JPEG" exception... and there are time I have over 1000 pics in directory). Thanks

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  • JVM missing Rhino

    - by Andrei
    I have a project that uses the ScriptEngine to process some javascript, and worked well on my machine, but when i send the projects's jar to the server, i had discovered that the server's JVM doesn't have Rhino built-in, returning null when the code calls a new ScriptEngineManager().getEngineByName("javascript"); I went to the rhino's download page, get the most recent version, and extracted the js.jar from it, added the jar on the project, but still have the same problem.

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  • Testing SocketChannel NIO

    - by hotzen
    Hello, I just wrote some NIO-code and wonder how to stress-test my implementation regarding SocketChannel.write(ByteBuffer) not able to write the whole byte-buffer SocketChannel.read(ByteBuffer) reading the data in chunks into ByteBuffer are there some simple linux-utilities like telnet to open a ServerSocket with some buffering-options?

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  • Wicket and Spring Intergation

    - by Vinothbabu
    I have a wicket contact form, and i receive the form object. Now i need to pass this object to Spring Service. package com.mysticcoders.mysticpaste.web.pages; import org.apache.wicket.markup.html.WebPage; import org.apache.wicket.markup.html.form.Form; import org.apache.wicket.markup.html.form.TextField; import org.apache.wicket.markup.html.panel.FeedbackPanel; import com.mysticcoders.mysticpaste.model.Contact; import org.apache.wicket.model.CompoundPropertyModel; import com.mysticcoders.mysticpaste.services.IContact; public class FormPage extends WebPage { private Contact contact; private IContact icontact; public FormPage() { // Add a FeedbackPanel for displaying our messages FeedbackPanel feedbackPanel = new FeedbackPanel("feedback"); add(feedbackPanel); Form<Object> form = new Form<Object>("contactForm", new CompoundPropertyModel<Object>(contact)) { private static final long serialVersionUID = 1L; protected void onSubmit(Contact contact) { icontact.saveContact(contact); } }; form.add(new TextField<Object>("name")); form.add(new TextField<Object>("email")); form.add(new TextField<Object>("country")); form.add(new TextField<Object>("age")); add(form); // add a simple text field that uses Input's 'text' property. Nothing // can go wrong here } } I am pretty much sure that we need to do something with application-context xml where i may need to wire out. My Application-context.xml <?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:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd"> <bean id="WicketApplication" class="com.mysticcoders.mysticpaste.web.pages.WicketApplication" /> </beans> My Question is simple. What should i do which can make my onSubmit method call the Spring Service? Could someone let me know what needs to modified in my Application-context.xml so that once the form gets submitted, it contacts the Spring Service class.

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  • in a J2EE application when does a listener get called?

    - by josh
    I have a J2EE app and it has a listener in web.xml. Listener contains a method called contextInitialized I want to know when does contextInitialized actually get called? From my reading I understand that it gets called when deploying the application. Can there be situations/scenario's where it could be called after the application has been deployed? Say that I am in a Clustered GlassFish app server environment. Could it be called after the application has been deployed?

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  • How do I migrate a ManyToOne to a ManyToMany relationship in Hibernate?

    - by spderosso
    I have a instance field of a class X that is mapped using Hibernate as a Many to One relationship. E.g: public class X{ ... @ManyToOne(optional=false) private Y iField; ... } That is correctly working with a particular schema. I know want to change this instance field iField to a List and a Many to Many relationship. public class X{ ... @ManyToMany(optional=false) private List<Y> iField; ... } What steps should I follow? Do I have to change the schema? in which way? In case you need more info let me know. Thanks!

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  • Multiplication of 2 positive numbers giving a negative result

    - by krandiash
    My program is an implementation of a bloom filter. However, when I'm storing my hash function results in the bit array, the function (of the form f(i) = (a*i + b) % m where a,b,i,m are all positive integers) is giving me a negative result. The problem seems to be in the calculation of a*i which is coming out to be negative. Ignore the print statements in the code; those were for debugging. Basically, the value of temp in this block of code is coming out to be negative and so I'm getting an ArrayOutOfBoundsException. m is the bit array length, z is the number of hash functions being used, S is the set of values which are members of this bloom filter and H stores the values of a and b for the hash functions f1, f2, ..., fz. public static int[] makeBitArray(int m, int z, ArrayList<Integer> S, int[] H) { int[] C = new int[m]; for (int i = 0; i < z; i++) { for (int q = 0; q < S.size() ; q++) { System.out.println(H[2*i]); int temp = S.get(q)*(H[2*i]); System.out.println(temp); System.out.println(S.get(q)); System.out.println(H[2*i + 1]); System.out.println(m); int t = ((H[2*i]*S.get(q)) + H[2*i + 1])%m; System.out.println(t); C[t] = 1; } } return C; } Any help is appreciated.

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  • Is it possible to inject a bean into a spring form bean

    - by Mike
    I tried to do it 2 different ways, but neither way worked. @Component public class EmailForm{ ... private QuestionDAO questionDAO; ... @Autowired public void setQuestionDAO(QuestionDAO questionDAO) { this.questionDAO = questionDAO; } ... Another way: @Component public class EmailForm implements ApplicationContextAware { ... public void setApplicationContext(ApplicationContext applicationContext) throws BeansException { this.questionDAO = (QuestionDAO)applicationContext.getBean("questionDAO"); } ... Neither way results in questionDAO being injected Form bean is populated by spring: @RequestMapping(method = RequestMethod.POST) public String submit(@Valid final EmailForm emailForm, BindingResult result, final Model model) {

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  • Error of iterator in mys JSP

    - by Mercer
    Hello, in my jsp i do this <table> <tr> <th>TITLLE</th> </tr> <tr class="row0"> <logic:iterate id="listClient" name="Client"> <td> [...] </td> </logic:iterate> </tr> </table> <logic:iterate id="listClient" name="Client"> <table> <tr> <td> [...] </td> </tr> </table> </logic:iterate> But i have this error for my second iterate javax.servlet.jsp.JspException: Cannot create iterator for this collection

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  • Ask Basic Configurator in Apache Commong Log

    - by adisembiring
    I use log4j as logger for my web application. in log4j, I can set the level log in log4j properties or log4j.xml. in log4j, we instance logger as follows: static Logger logger = Logger.getLogger(SomeClass.class); I init log4j basic configurator in a servlet file using init method. But, I usually test application using JUnit, So I init the basic configurator in setup method. after that, I test the application, and I can see the log. Because I deployed, the web in websphere. I change all of logging instance become: private Log log = LogFactory.getLog(Foo.class); I don't know how to load basic configurator using ACL. so I can't control debug level to my JUnit test. do you have any suggestion, without changing static Logger logger = Logger.getLogger(SomeClass.class); become static Logger logger = Logger.getLogger(SomeClass.class);

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  • Launch .jar files with command line arguments (but with no console window)

    - by Virat Kadaru
    I have to do a demo of an application, the application has a server.jar and client.jar. Both have command line arguments and are executable. I need to launch two instances of server.jar and two instances of client.jar. I thought that using a batch file was the way to go, but, the batch file executes the first command (i.e. server.bat [argument1] [argument2]) and does not do anything else unless I close the first instance, in which case it then runs the 2nd command. And also the I do not want a blank console window to open (or be minimized) What I really need is a batch script that will just launch these apps without any console windows and launch all instances that I need. Thanks in Advance! EDIT: javaw: works if I type the command into the console window individually. If I put the same in the batch file, it will behave as before. Console window opens, one instance starts (whichever was first) and it does not proceed further unless I close the application in which case it runs the 2nd command. I want it to run all commands silently SOLUTION: Found the solution, below is the contents of my batch file @echo off start /B server.jar [arg1] [arg2] start /B server.jar [arg3] [arg4] @echo on this opens, runs all the commands and closes the window, does not wait for the command to finish.

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  • Specifying distinct sequence per table in Hibernate on subclasses

    - by gutch
    Is there a way to specify distinct sequences for each table in Hibernate, if the ID is defined on a mapped superclass? All entities in our application extend a superclass called DataObject like this: @MappedSuperclass public abstract class DataObject implements Serializable { @Id @GeneratedValue(strategy = GenerationType.SEQUENCE) @Column(name = "id") private int id; } @Entity @Table(name = "entity_a") public class EntityA extends DataObject { ... } @Entity @Table(name = "entity_b") public class EntityB extends DataObject { ... } This causes all entities to use a shared sequence, the default hibernate_sequence. What I would like to do is use a separate sequence for each entity, for example entity_a_sequence and entity_b_sequence in the example above. If the ID were specified on the subclasses then I could use the @SequenceGenerator annotation to specify a sequence for each entity, but in this case the ID is on the superclass. Given that ID is in the superclass, is there a way I can use a separate sequence for each entity — and if so, how? (We are using PostgreSQL 8.3, in case that's relevant)

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  • JUnitCore.runClasses doesn't print anything....

    - by Grégoire
    I have a test class that I'm trying to run from a main method with the folowing code : Result r = org.junit.runner.JUnitCore.runClasses(TestReader.class); when I examine the Result object I can see that 5 tests have been run but nothing is printed on the screen. Should I do something else to get an output ?

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  • Perf4J Graph Output from Log File

    - by manyxcxi
    I currently have a long running process that I am trying to analyze with Perf4J. I currently have it writing results in CSV format to its own log file using the AsyncCoalescingStatisticsAppender and a StatisticsCsvLayout on the file appender. My question is; when I try and use the --graph option from the command line (using the perf4j jar) it isn't populating the data points- it isn't populating anything. Are my appenders set incorrectly? The log file contains hundreds (sometimes thousands) of data points of about 10 different tag names. <appender name="perfAppender" class="org.apache.log4j.FileAppender"> <param name="File" value="perfStats.log"/> <layout class="org.perf4j.log4j.StatisticsCsvLayout"> </layout> </appender> <appender name="CoalescingStatistics" class="org.perf4j.log4j.AsyncCoalescingStatisticsAppender"> <!-- The TimeSlice option is used to determine the time window for which all received StopWatch logs are aggregated to create a single GroupedTimingStatistics log. Here we set it to 10 seconds, overriding the default of 30000 ms --> <param name="TimeSlice" value="10000"/> <appender-ref ref="ConsoleAppender"/> <appender-ref ref="CompositeRollingFileAppender"/> <appender-ref ref="perfAppender"/> </appender>

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  • String Manipulation: Spliting Delimitted Data

    - by Milli Szabo
    I need to split some info from a asterisk delimitted data. Data Format: NAME*ADRESS LINE1*ADDRESS LINE2 Rules: 1. Name should be always present 2. Address Line 1 and 2 might not be 3. There should be always three asterisks. Samples: MR JONES A ORTEGA*ADDRESS 1*ADDRESS2* Name: MR JONES A ORTEGA Address Line1: ADDRESS 1 Address Line2: ADDRESS 2 A PAUL*ADDR1** Name: A PAUL Address Line1: ADDR1 Address Line2: Not Given My algo is: 1. Iterate through the characters in the line 2. Store all chars in a temp variables until first * is found. Reject the data if no char is found before first occurence of asterisk. If some chars found, use it as the name. 3. Same as step 2 for finding address line 1 and 2 except that this won't reject the data if no char is found My algo looks ugly. The code looks uglier. Spliting using //* doesn't work either since name can be replaced with address line 1 If the data is *Address 1*Address2, split will create two indexes in the array where index 0 will have the value of Address 1 and index 2 will have the value of Address2. Where's the name. Was there a name? Any suggestion?

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  • Is it safe to reuse javax.xml.ws.Service objects

    - by Noel Ang
    I have JAX-WS style web service client that was auto-generated with the NetBeans IDE. The generated proxy factory (extends javax.xml.ws.Service) delegates proxy creation to the various Service.getPort methods. The application that I am maintaining instantiates the factory and obtains a proxy each time it calls the targetted service. Creating the new proxy factory instances repeatedly has been shown to be expensive, given that the WSDL documentation supplied to the factory constructor, an HTTP URI, is re-retrieved for each instantiation. We had success in improving the performance by caching the WSDL. But this has ugly maintenance and packaging implications for us. I would like to explore the suitability of caching the proxy factory itself. Is it safe, e.g., can two different client classes, executing on the same JVM and targetting the same web service, safely use the same factory to obtain distinct proxy objects (or a shared, reentrant one)? I've been unable to find guidance from either the JAX-WS specification nor the javax.xml.ws API documentation. The factory-proxy multiplicity is unclear to me. Having Service.getPort rather than Service.createPort does not inspire confidence.

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