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• Negative logical shift

  - by user320862

  In Java, why does -32 -1 = 1 ? It's not specific to just -32. It works for all negative numbers as long as they're not too big. I've found that x -1 = 1 x -2 = 3 x -3 = 7 x -4 = 15 given 0 x some large negative number Isn't -1 the same as << 1? But -32 << 1 = -64. I've read up on two's complements, but still don't understand the reasoning.

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• BlueJ Chpt 4 - Auction Project - How to make removeLot method work after entering a new lot

  - by Ellaine Ryan

  Hi All I am learning Java through BlueJ I would like to add a removeLot method to the Auction Class in BlueJ Chpt 4. This involves also returning the lot with the given number or null if there is no such lot. If you enter , say 5 lots and then use the remove method, this codes removes whichever lot you specify. However if you enter a new lot after using the removeLot method - an internal error message comes up regarding lotnumbering . Any ideas? Thanks Elaine public Lot removeLot(int number) { if((number >= 1) ) { } Lot lot = getLot (number); if(lot !=null) { lots.remove(lot); } return lot; }

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• Findbugs warning: Equals method should not assume anything about the type of its argument

  - by Uri

  When running FindBugs on my project, I got a few instances of the error described above. Namely, my overriding versions of equals cast the RHS object into the same type as the object in which the overriding version is defined. However, I'm not sure whether a better design is possible, since AFAIK Java does not allow variance in method parameters, so it is not possible to define any other type for the equals parameter. Am I doing something very wrong, or is FindBugs too eager? A different way to phrase this question is: what is the correct behavior if the object passed to equals is not the same type as an LHS: Is this a false, or should there be an exception? For example: public boolean equals(Object rhs) { MyType rhsMyType = (MyType)rhs; // Should throw exception if(this.field1().equals(rhsMyType.field1())... // Or whatever }

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• Dynamic programming: Largest diamond(rhombus) block

  - by Darksody

  I have a small program to do in Java. I have a 2D array filled with 0 and 1, and I must find the largest rhombus (as in square rotated by 90 degrees) and their numbers. Example: 0 1 0 0 0 1 1 0 1 1 1 0 1 0 1 1 1 1 0 1 1 1 1 1 0 0 1 1 1 1 1 1 1 1 1 1 Result: 1 1 1 1 1 1 1 1 1 1 1 1 1 The problem is similar to this SO question. If you have any idea, post it here.

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• OJB / Oracle XE sql debug-display problem

  - by Jay

  Hello, I have a Java application, and use OJB as my ORM technology. I have an Oracle XE installation locally to develop against. The problem is when I need to debug a problem, I like looking at the SQL output. Here is an example of SQL I can view through the "Top SQL" interface in Oracle XE: select a_bunch_of_fields from KREW_DOC_TYP_T A0 WHERE ((UPPER(A0.DOC_TYP_NM) LIKE :1) AND A0.ACTV_IND = :2) AND A0.CUR_IND = :3 The problem is I would like to see the real value instead of ":1". I can't seem to find how I can configure this. I know the real values are working, because the application is responding as expected, for the most part (hence the bugs I am working on). Thanks, Jay

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• How to find multiples of the same integer in an arraylist?

  - by Dan

  Hi My problem is as follows. I have an arraylist of integers. The arraylist contains 5 ints e.g[5,5,3,3,9] or perhaps [2,2,2,2,7]. Many of the arraylists have duplicate values and i'm unsure how to count how many of each of the values exist. The problem is how to find the duplicate values in the arraylist and count how many of that particular duplicate there are. In the first example [5,5,3,3,9] there are 2 5's and 2 3's. The second example of [2,2,2,2,7] would be only 4 2's. The resulting information i wish to find is if there are any duplicates how many of them there are and what specific integer has been duplicated. I'm not too sure how to do this in java. Any help would be much appreciated. Thanks.

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• Develop applications to mobiles

  - by muek

  Hi there, I have very easy question, but I simply have any idea of the answer. I have developed a small mobile-application using java, for my nokia. The problem is that when installed on my samsung the application simply crashed. Then I tried on my other nokia but different model, and I didn't got the normal behavior. So my question is, does anyone have any idea how companies that develop mobiles applications/games test their software. Does they have to have all models for all mobiles phones??

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• getting core file

  - by ashwani66476

  Hello All I am running a Core JAVA application on AIX machine, and it creates a file named "core". My concern are 1. I am not able to open this "core" file in "Heap Analyzer" or "Thread Analyzer". 2. Which tools do I need to use, So that I can analyze this "core" file. 3. Could any one elaborate more about this file? why this "core" file creates. Waiting for response..... Many Thanks

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• Dev efforts for different mobile platforms

  - by Juriy

  Hello guys, I'm in the middle of development of a client-server "socializing" that is supposed to run on several mobile devices. The project is pretty complex, involving networking, exchanging media, using geolocation services, and nice user UI. In terms of development efforts, technical risks and extensibility what is the best platform to start with? Taking into the account that the goal is go "live" as fast as possible with the mobile version. And second goal is to cover most users (but first is more important). iPhone (iPod iPad) Android BlackBerry Java ME, Symbian I realize that there are limitations on every platform, and there are different aspects to take into the account (for example iPhone has better developer's community then Android, J2ME runs in a terrible sandbox but covers most devices). Please share your pros and cons. I have the experience only with J2ME, unfortunately I can't evaluate other platforms.

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• Twitter date unparseable?

  - by Andreas

  Hi, I want to convert the date string in a Twitter response to a Date object, but I always get a ParseException and I cannot see the error!?! Input string: Thu Dec 23 18:26:07 +0000 2010 SimpleDateFormat Pattern: EEE MMM dd HH:mm:ss ZZZZZ yyyy Method: public static Date getTwitterDate(String date) { SimpleDateFormat sf = new SimpleDateFormat(TWITTER); sf.setLenient(true); Date twitterDate = null; try { twitterDate = sf.parse(date); } catch (Exception e) {} return twitterDate; } I also tried this: http://friendpaste.com/2IaKdlT3Zat4ANwdAhxAmZ but that gives the same result. I use Java 1.6 on Mac OS X. Cheers, Andi

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• Which build tool to teach?

  - by Helper Method

  While similiar questions have been asked, this one's focused on which is best/easiest to teach. I'm giving a weekly tutorial at my university focusing on data structures and algorithms. Fromn time to time I introduce tools which may prove helpful in future projects like JUnit, Mercurial, Eclipse etc.. I plan to show them some kind of build tool but I'm not sure which one to choose. I by myself have very little knowledge about build tools, except a little experience in using make. It's more the concept of a build tool I want to show them, not a special tool per se. Which would be the most easiest/future proof/whatever tool to show them? I've read a little bit about Gradle, which looks nice, but so far I think Ant could be a good choice (it's a Java course I'm giving).

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• Dynamic programming: Find largest diamond (rhombus)

  - by Darksody

  I have a small program to do in Java. I have a 2D array filled with 0 and 1, and I must find the largest rhombus (as in square rotated by 90 degrees) and their numbers. Example: 0 1 0 0 0 1 1 0 1 1 1 0 1 0 1 1 1 1 0 1 1 1 1 1 0 0 1 1 1 1 1 1 1 1 1 1 Result: 1 1 1 1 1 1 1 1 1 1 1 1 1 The problem is similar to this SO question. If you have any idea, post it here.

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• Are frameworks using byte-code generation creating leaky abstractions?

  - by Gabriel Šcerbák

  My point is, if you don't understand the abstraction of a framework, you can still decompile it and understand it, because you know the language e.g. Java. However, when byte-code generation happens, you have to understand even a lower level - JVM level byte-codes. I am really affraid of using any of such frameworks, which are many. Most of the time I think the reason for byte-code generation is simply lack of language features such as metaprogramming. Do you agree? What is your opinion and argument? How do you take over the problem with leaky abstractions in those frameworks?

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• Trying to debug a plugin in tuxguitar, need help building the project in Eclipse.

  - by Shawn Simon

  I am not too familiar with java / eclipse but I am trying to debug a plugin in TuxGuitar. The plugin is the gtp plugin which allows reading of guitar pro files. I have imported the main project, TuxGuitar, and the TuxGuitar-gtp plugin. I have all build dependencies configured and the project builds. However, when I debug the app, the plugin is not available. The documentation says plugins are loaded from the share/plugins folder and they are jar files. I tried exporting the gtp plugin as a jar into the share/plugins folder, but it still does not load when I debug. Is there some sort of configuration I need to do in Eclipse? Thanks!

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• Two BlockingQueue in the same endless loop?

  - by DrDol

  I have a thread, that processes incomming messages (endless loop). For this, I use a BlockingQueue (Java), which works as quite nice. Now, I want to add a second processor in the same Class oder method. The problem now is, that in the endless loop i have this part newIncomming = this.incommingProcessing.take(); This part blocks if the Queue is empty. I'm looking for a solution to process to queues in the same class. The second queue can only processed, it some data is coming in for the first Queue. Is there a way to handle tow blocking queues in the same endless loop?

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• How do I detect a loop in this linked list?

  - by jjujuma

  Say you have a linked list structure in Java. It's made up of Nodes: class Node { Node next; // some user data } and each Node points to the next node, except for the last Node, which has null for next. Say there is a possibility that the list can contain a loop - i.e. the final Node, instead of having a null, has a reference to one of the nodes in the list which came before it. What's the best way of writing boolean hasLoop(Node first) which would return true if the given Node is the first of a list with a loop, and false otherwise? How could you write so that it takes a finite amount of space and a reasonable amount of time?

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• strategies for learning complex software packages

  - by Tom

  I am a fairly novice Java programmer and I am currently working on a project to extend a piece of software that has been developed over a few years. So it has pretty big code base and the previous developers knew it well, so extending it is not going to be easy without a thorough understanding of the structure and function. 1) I had begun by trying to tackle small parts of the system and document them with mindmap. (particularly I am trying to document the interactions with external systems) 2) I have the book "code complete", which I am working through. 3) I have pointed some tools like "tattletale" at the code to get some diagrams of dependency relationships. What other strategies should I employ, should I focus on one particular aspect?

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• Grails/Spring HttpServletRequest synchronization

  - by Jeff Storey

  I was writing a simple Grails app and I have a spot in a gsp where one of my java beans in modified. <g:each in="${myList}" status="i" var="myVar"> // if the user performs some view action, update one of the myVar elements </g:each> This works, but I don't think it's quite threadsafe. myList is an http request variable but in cases of pages that use ajax (or other client side manipulations), it is possible for two threads to be modifying the same request scope variable The Spring AbstractController class provides a setSynchronizeOnSession method. Does grails provide any equivalent functionality? If not, what's the best way to protect this non-threadsafe mutation? thanks, Jeff

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• performance monitoring tools for multi-tenant web application

  - by Anton

  We have a need to monitor performance of our java web app. We are looking for some tolls which can help us with this task. The major difficulty is that we are SaaS provider with multi-tenant server architecture with hundreds of customers running on the same hardware. So far we tried commercial products like DynaTrace and Coradinat but unfortunately they don't get the job done so far. What we need is a simple report which would tell us if we had performance problems on each customer site in a specified period of time. Mostly it will be response time per customer but also we will need some more specifics based on the URLs. please let me know if someone had any experience with setting up such monitoring. Thanks!

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• Programming with midi, and tuning notes to specific frequencies

  - by froggie0106

  I am working on a project in which I need to be able to generate midi notes of varying frequencies with as much accuracy as possible. I originally tried to write my program in Java, but it turns out that the sound.midi package does not support changing the tunings of notes unless the frequencies are Equal Tempered frequencies (or at least it didn't in 1.4, and I haven't been able to find evidence that this has been fixed in recent versions). I have been trying to find a more appropriate language/library to accomplish this task, but since this is my first time programming with MIDI and my need for specific tuning functionality is essential, I have been having considerable trouble finding exactly what I need. I am looking for advice from people who have experience writing MIDI programs as to what languages are useful, especially for tuning notes to specific frequencies. Any links to websites with API docs and example code would also be extremely helpful.

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• Will client JVM for a web service(https) throw an SSL Exception when the server is having a valid ce

  - by ring bearer

  I have a web service deployed on tomcat hosted on a remote server. I have set it up such that it can be accessed only via HTTPS. For this, I generated a Certificate Signing Request (CSR) and used it to get a temporary certificate from VeriSign. My web service client is on my local machine. If I try to access the service it will throw a javax.net.ssl.SSLHandshakeException:unable to find valid certification path to requested target If I install the certificate in to local Java's keystore, the issue will be resolved. My question is if I install a valid SSL certificate from a CA in to my tomcat server, will I get this client-side error even if I do not import the certificate to local key store?

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• How to leverage Spring Integration in a real-world JMS distributed architecture?

  - by ngeek

  For the following scenario I am looking for your advices and tips on best practices: In a distributed (mainly Java-based) system with: many (different) client applications (web-app, command-line tools, REST API) a central JMS message broker (currently in favor of using ActiveMQ) multiple stand-alone processing nodes (running on multiple remote machines, computing expensive operations of different types as specified by the JMS message payload) How would one best apply the JMS support provided by the Spring Integration framework to decouple the clients from the worker nodes? When reading through the reference documentation and some very first experiments it looks like the configuration of an JMS inbound adapter inherently require to use a subscriber, which in a decoupled scenario does not exist. Small side note: communication should happen via JMS text messages (using a JSON data structure for future extensibility).

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• Wicket app in embedded Jetty causes UnsupportedClassVersionError

  - by Ondra Žižka

  I've tried to run a Wicket app in an embedded Jetty, using this code: public static void main( String[] args ){ Server server = new Server(8080); Context root = new Context( server, "/", Context.SESSIONS ); FilterHolder filterHolder = new FilterHolder( new WicketFilter() ); filterHolder.getInitParameters().put("applicationClassName", cz.dw.test.WicketApplication.class.getName() ); root.addFilter( filterHolder, "/*" , Handler.ALL ); try { server.start(); } catch (Exception ex) { ex.printStackTrace(); } } But I got java.lang.UnsupportedClassVersionError: Bad version number in .class file. Switching the target class version for my app (1.6 - 1.5) did not help. I use Sun JDK 1.6.0_17, Wicket 1.4.8, Jetty 6.1.24. I tried to debug, but the JRE classes have no debug data. The stacktrace is of no use as it happens when loading the classes into JVM. Any ideas what could be wrong? How can I find which class is causing this? Thanks, Ondra

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• How to get some xml that comes before and a little from after a DOM Node.

  - by startoftext

  I am using java and I am pretty open to using w3c DOM or DOM4J at this point. So lets say I have a Node like a text node that I have found something interesting in, like say an occurrence of a substring in the nodes text. If I want to get a string with a number characters preceding that node and a few characters after that node how may I do that? Basically I need to be able to display a snippet of the original xml around the occurrence of that string. The problem I have with getting the parent node for example and then calling asXML is that I no longer know the exact location of the substring in the text node. If I search again for that string value in the parents xml then I may find 2 occurrences or many more if the parent has other children that contain an occurrence of that string. Much appreciation if any one can answer this question.

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• Using @NotNull in a project where both IntelliJ and Eclipse developers are working

  - by Gugussee

  A co-worker on IntelliJ IDEA (working on another project) showed me the amazing @NotNull annotation. I've read messages here on SO about how starting to add @NotNull everywhere saved lots of time and headaches (and IntelliJ 10 can even add automatically @NotNull to old code when it detects that null would break havoc). Since I read my first "Probable @NotNull violation" message (in real-time, in the IDE, even on a partial .java file that doesn't compile yet) my jaw dropped and I got hooked. So I was wondering: is there anything that needs to be known if we want to start using @NotNull in a project where developers are using both Eclipse and IntelliJ? I know IntelliJ ships with the annotations.jar. Is this compatible with Eclipse?

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