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  • Measuring the time to create and destroy a simple object

    - by portoalet
    From Effective Java 2nd Edition Item 7: Avoid Finalizers "Oh, and one more thing: there is a severe performance penalty for using finalizers. On my machine, the time to create and destroy a simple object is about 5.6 ns. Adding a finalizer increases the time to 2,400 ns. In other words, it is about 430 times slower to create and destroy objects with finalizers." How can one measure the time to create and destroy an object? Do you just do: long start = System.nanoTime(); SimpleObject simpleObj = new SimpleObject(); simpleObj.finalize(); long end = System.nanoTime(); long time = end - start;

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  • How to search for duplicate values in a huge text file having around Half Million records

    - by Shibu
    I have an input txt file which has data in the form of records (each row is a record and represents more or less like a DB table) and I need to find for duplicate values. For example: Rec1: ACCOUNT_NBR_1*NAME_1*VALUE_1 Rec2: ACCOUNT_NBR_2*NAME_2*VALUE_2 Rec3: ACCOUNT_NBR_1*NAME_3*VALUE_3 In the above set, the Rec1 and Rec2 are considered to be duplicates as the ACCOUNT NUMBERS are same(ACCOUNT_NBR1). Note: The input file shown above is a delimiter type file (the delimiter being *) however the file type can also be a fixed length file where each column starts and ends with a specified positions. I am currently doing this with the following logic: Loop thru each ACCOUNT NUMBER Loop thru each line of the txt file and record and check if this is repeated. If repeated record the same in a hashtable. End End And I am using 'Pattern' & 'BufferedReader' java API's to perform the above task. But since it is taking a long time, I would like to know a better way of handling it. Thanks, Shibu

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  • Apache HTTPClient returns an empty page

    - by mariosangiorgio
    Hi, I am using the Apache HTTPClient for Java and I'm facing a really strange issue. Sometimes when I try to get a dynamically generated page it returns its actual content, but other times (with another parameter) all I get is a short sequence of \t,\r and \n. How could I track what's going on on the different cases in order to find where is the bug? My usage of the library is pretty straightforward, all I do is this few calls on an initialized HTTPClient object: String content = "/pageIwant.jsp?parameter=10101010"; HttpGet request = new HttpGet(content); HttpResponse response = client.execute(targetHost, request); HttpEntity entity = response.getEntity(); String page = EntityUtils.toString(entity);

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  • Integer v/s int

    - by Siddhartha
    Read this on the oracle docs java.lang page: Frequently it is necessary to represent a value of primitive type as if it were an object. The wrapper classes Boolean, Character, Integer, Long, Float, and Double serve this purpose. I'm not sure I understand why these are needed. It says they have useful functions such as equals(). But if I can do (a==b), why would I ever want to declare them as Integer, use more memory and use equals()? How does the memory usage differ for the 2?

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  • How to start an Open Source Software development

    - by harigm
    I have an idea to start a Open Source Software using Java and PHP, I am so sure that software will help many individuals in their daily routine. Can Any one suggest me how to start the process ? Do we need to register some where and submit our idea for an approval before we start development? Any license that we need to get? How to invite the people for the open source development community, if they are interested? If any people who contributes Do we need to get any agreement signed off? once the Open Source product is stabilized who will have the ownership?

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  • Hibernate, select by id or unique column

    - by Nican
    I am using hibernate for Java, and I want to be able to select users by id or by name from the database. Nice thing about Hibernate is that it caches the result by id, but I seem to be unable to make it cache by name. static Session openSession = Factory.openSession(); public static User GetUser(int Id) { return (User) openSession.get(User.class, new Integer(Id)); } public static User GetUser( String Name ){ return (User) openSession.createCriteria( User.class ). add( Restrictions.eq("username", Name) ). uniqueResult(); } If I use GetUser(1) many times, hibernate will only show that it executed the first time. But every time I use GetUser("user1"), hibernate shows that it is executing a new query to database. What would be the best way to have the string identifier be cached also?

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  • How to set the component size with GridLayout? Is there a better way?

    - by Blackbam
    Hello guys, I am working on a larger GUI with Java and I am becoming angry on Layout Managers. I have a "Settings-Panel" with a variable number of JComponents in it (Labels, Buttons, JSpinners, JSliders,...). I just want the following: JLabel <- JComponent JLabel <- JComponent JLabel <- JComponent ... My Panel has a size of 500px, so that there is enough space for a lot of components. Unfortunatly the GridLayout always stretches the size of the Components to the whole Panel, even if I set a MaximumSize for every component. It looks stupid if there are only two buttons each with a height of 250px. I tried flow Layout, but i cannot figure out a way to make new lines properly. I tried BoxLayout.Y_AXIS, but the Components are always centered, and Label and Component are not in the same line. Does anybody know a good and short way with LayoutManagers to handle this properly?

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  • Does this game have a solution

    - by Bragboy
    Hi, I am developing a simple game using Java swing. I want to know whether this particular game has a solution in the following scenario. If I am convinced that theoretically a solution cannot be arrived at this point, I will throw a notification to the user. 3x3 4x4 The objective of this game is to fill numbers from 1 to 8 (or 1 to 15) using the one space available to push the numbers to that empty space. Every time I end up with the combination shown above. I just want to convince myself that there is no way to attain the proper solution from the above scenario. Please help. EDIT : Solution has been posted at here and here

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  • Persisting non-entity class that extends an entity (jpa) - example?

    - by Michal Minicki
    The JPA tutorial states that one can have a non-entity that extends entity class: Entities may extend both entity and non-entity classes, and non-entity classes may extend entity classes. - http://java.sun.com/javaee/5/docs/tutorial/doc/bnbqa.html Is it possible to persist such structure? I want to do this: @Entity abstract class Test { ... } class FirstConcreteTest extends Test { ... } // Non-ntity class SecondConcreteTest extends Test { ... } // Non-entity Test test = new FirstConcreteTest(); em.persist(test); What I would like it to do is to persist all fields mapped on abstract Test to a common database table for all concrete classes (first and second), leaving all fields of first and second test class unpersisted (these can contain stuff like EJBs, jdbc pools, etc). And a bonus question. Is it possible to persist abstract property too? @Entity abstract class Test { @Column @Access(AccessType.PROPERTY) abstract public String getName(); } class SecondConcreteTest extends Test { public String getName() { return "Second Concrete Test"; } }

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  • any ways saving user information without db

    - by hguser
    Hi: I have a application which require login,but the number of user who use the application is no more than 40. And In the application,I get some data from the sql server database where I juse have read permission,also I can not create a table in the db for user validate. ALso I do not think it is a good idea to create a user table in other database on another machine.(for example,I can create a user table in the mysql another machine,but is it desireable just for user validating)? Now I just save the user info in a .properties file,any other good idea? BTW,the programe language used in my application is java.

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  • Full GC real time is much more that user+sys times

    - by Stas
    Hi. We have a Web Java based application running on JBoss with allowed maximum heap size of about 1.2 GB (total machine physical memory is 2 GB). At some point the application stops responding (to clients) for several minutes. After some analysis we found out that the culprit is the Full GC. Here's an excerpt from the verbose GC log: 74477.402: [Full GC [PSYoungGen: 3648K-0K(332160K)] [PSOldGen: 778476K-589497K(819200K)] 782124K-589497K(1151360K) [PSPermGen: 102671K-102671K(171328K)], 646.1546860 secs] [Times: user=3.84 sys=3.72, real=646.17 secs] What I don't understand is how is it possible that the real time spent on Full GC is about 11 minutes (646 seconds), while user+sys times are just 7.5 seconds. 7.5 seconds sound to me much more logical time to spend for cleaning <200 MB from the old generation. Where does all the other time go? Thanks a lot.

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  • Selecting item from set given distribution

    - by JH
    I have a set of X items such as {blower, mower, stove} and each item has a certain percentage of times it should be selected from the overall set {blower=25%,mower=25%,stove=75%} along with a certain distribution that these items should follow (blower should be selected more at the beginning of selection and stove more at the end). We are given a number of objects to be overall selected (ie 100) and a overall time to do this in (say 100 seconds). I was thinking of using a roulette wheel algorithm where the weights on the wheel are affected by the current distribution as a function of the elapsed time (and the allowed duration) so that simple functions could be used to determine the weight. Are there any common approaches to problems like this that anyone is aware of? Currently i have programmed something similar to this in java using functions such as x^2 (with correct normalization for the weights) to ensure that a good distribution occurs. Other suggestions or common practices would be welcome :-)

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  • How to analyse Dalvik GC behaviour?

    - by HRJ
    I am developing an application on Android. It is a long running application that continuously processes sensor data. While running the application I see a lot of GC messages in the logcat; about one every second. This is most probably because of objects being created and immediately de-referenced in a loop. How do I find which objects are being created and released immediately? All the java heap analysis tools that I have tried(*) are bothered with the counts and sizes of objects on the heap. While they are useful, I am more interested in finding out the site where temporary short-lived objects get created the most. (*) I tried jcat and Eclipse MAT. I couldn't get hat to work on the Android heap-dumps; it complained of an unsupported dump file version.

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  • lookahead and group

    - by Istao
    Hi, In Java, on a text like foo <on> bar </on> thing <on> again</on> now, I should want a regex with groups wich give me with a find "foo", "bar", empty string, then "thing", "again", "now". If I do (.*?)<on>(.*?)</on>(?!<on>), I get only two group (foo bar, thing again, and I've not the end "now"). if I do (.*?)<on>(.*?)</on>((?!<on>)) I get foo bar empty string, then thing again and empty string (here I should want "now"). Please what is the magical formula ? Thanks.

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  • MVC Framework for existing application.

    - by Dhruva
    I am modifying existing java web application that was written long time ago, and it is written in the wrost possible way. It has business logic and sql statemens in JSP files. Because of the certain constraint, I can not re-design the entire application. but I can implement better design in any new feature that I add. can anybody suggest me any MVC framework that I could easily integrate in existing app. I need to have framework that is not depended on many external jar files and it does not cause any issues with existing application.

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  • Creating reference movies for iPhone on the fly

    - by Mad Oxyn
    We are working on an online mobile video app. The videos we want to play on mobile phones are being generated by a server, as there can be dynamic content in the server (based on user input). Now for iPhone we would like to play the video in the best possible resolution based on the connection speed at the time of downloading the movie. This can be done using reference movies. However, because our videos are being generated on the fly, we need to generate this reference movie on the fly as well. Is there a way to generate reference movies on the fly on a Linux server using some command line tool, PHP or Java? Or on a DOS server maybe? Any help will be much appreciated.

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  • Web.xml ExceptionType

    - by andrew007
    Hi, is it possible to define two sections in the web.xml in order to catch two different exception types: <!-- general exception --> <error-page> <exception-type>**java.lang.Exception**</exception-type> <location>/generalError.jsp</location> </error-page> <!-- specific exception --> <error-page> <exception-type>org.myapp.myException</exception-type> <location>/sessionTimeout.jsp</location> </error-page> Does it has any conflict? THANKS!

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  • Mapping tables from an existing database to an object -- is Hibernate suited?

    - by Bernhard V
    Hello! I've got some tables in an existing database and I want to map them to a Java object. Actually it's one table that contains the main information an some other tables that reference to such a table entry with a foreign key. I don't want to store objects in the database, I only want to read from it. The program should not be allowed to apply any changes to the underlying database. Currently I read from the database with 5 JDBC sql queries and set the results then on an object. I'm now looking for a less code intensive way. Another goal is the learning aspect. Is Hibernate suitable for this task, or is there another ORM framework that better fits my requirement?

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  • GWT: Loading different UI's based on URL

    - by jmccartie
    Trying to get a GWT project off the ground and finding it difficult to do any basic routing. Trying to fire up different UI's based on the URL. Thought I could set a string based on the getHash() and then switch off that, but seems cumbersome (and annoying since I can't do string-based switches in Java). There's got to be a best practice for this. I know Gerrit uses hashes for determining this type of information but couldn't find where they do it in the source. Or is this totally not GWT-related? Something I can handle in web.xml? Any help is much appreciated.

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  • URLEncode Error

    - by user2949519
    I have an Android app. Basically what it does is that user can search a car reference no. in EditText for example:- 270/30 and retrieve all the details of the particular car with the same column value in the database. I'm encoding this editext value in Android using URLEncoder and decoding it back in php webservice code. But the decoded value im getting is 027/13 ....instead of 270/30. To make it clear more im here by pasting my java Encoding part EditText SearchField=(EditText)findViewById(R.id.editText1); String SearchValue= SearchField.getText().toString(); Now the encoding code in Asynctask is data +="&" + URLEncoder.encode("data", "UTF-8") + "="+SearchValue; Now the PHP part where i decoded this code $data = urldecode($_POST['data']); Please help me how to encode/decode this given format ... Thanks in Advance

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  • Behavior of nested finally in Exceptions

    - by kuriouscoder
    Hello: Today at work, I had to review a code snippet that looks similar to this mock example. package test; import java.io.IOException; import org.apache.log4j.Logger; public class ExceptionTester { public static Logger logger = Logger.getLogger(ExceptionTester.class); public void test() throws IOException { new IOException(); } public static void main(String[] args) { ExceptionTester comparator = new ExceptionTester(); try { try { comparator.test(); } finally { System.out.println("Finally 1"); } } catch(IOException ex) { logger.error("Exception happened" ex); // also close opened resources } System.out.println("Exiting out of the program"); } } It's printing the following output.I expected an compile error since the inner try did not have a catch block. Finally 1 Exiting out of the program I do not understand why IOException is caught by the outer catch block. I would appreciate if anyone can explain this, especially by citing stack unwinding process

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  • Access of private field of another object in copy constructors - Really a problem?

    - by DR
    In my Java application I have some copy-constructors like this public MyClass(MyClass src) { this.field1 = src.field1; this.field2 = src.field2; this.field3 = src.field3; ... } Now Netbeans 6.9 warns about this and I wonder what is wrong with this code? My concerns: Using the getters might introduce unwanted side-effects. The new object might no longer be considered a copy of the original. If it is recommended using the getters, wouldn't it be more consistent if one would use setters for the new instance as well?

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  • is opening and closing of factory contolled by web.xml?

    - by akshay
    This post is related to post InvalidStateException while trying to enter data into DB. Do i need to put some entries in web.xml?Does web.xml control opening and closing of factory?I saw folloing entries in web.xml of another similar project . <resource-ref> <res-ref-name>jms/XYConnectionFactory</res-ref-name> <res-type>javax.jms.ConnectionFactory</res-type> <res-auth>Container</res-auth> <res-sharing-scope>Unshareable</res-sharing-scope></resource-ref> <resource-env-ref> <resource-env-ref-name>rep/xyAppConfig</resource-env-ref-name> <resource-env-ref-type>java.util.Map</resource-env-ref-type></resource-env-ref> What does this entries do?

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  • HTML J2ME Problem

    - by Hesham
    i'm trying to put large amount of data in a java me application for a BlackBerry mobile and i noticed that the max file size to be accepted in BlackBerry is 150 KB, by the way i'm developping the application in arabic language so i'm converting every litter to his corresponding unicode so every char gets to 6 chars so its another big problem, some ppl told me that i can write arabic as arabic letters without the need to write its unicode, by viewing the mobile form as an html page, my problem is that i dont know how to view the page as html page and what is XMLParser ?? can anyone help me to get all this together, cos i really need some serious help thank you alot Hesham

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  • Suspend TimerTask until the next execution

    - by user1052518
    I am using a TimerTask to run some periodic tasks, the task being processing a set of files. I have a requirement where if the number of files to be processed exceeds a pre-determined limit, the thread suspends execution and waits till the next cycle to start processing the files again. Is there a way to suspend the TimerTask until the next execution period or do I have to extend the TimerTask class to achieve this functionality? I saw there is a TimerTask.cancel method, but this will cancel all further executions of this thread. I don't want this to happen. I just want the thread to be suspended until the next execution period. I don't have the luxury of moving to any of the other concurrent classes in Java as our framework uses TimerTask, and I have to stick with it. Any suggestions, pointers or tips are greatly appreciated. thanks, Asha

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