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  • How do I get Java to use my multi-core processor?

    - by Rudiger
    I'm using a GZIPInputStream in my program, and I know that the performance would be helped if I could get Java running my program in parallel. In general, is there a command-line option for the standard VM to run on many cores? It's running on just one as it is. Thanks! Edit I'm running plain ol' Java SE 6 update 17 on Windows XP. Would putting the GZIPInputStream on a separate thread explicitly help? No! Do not put the GZIPInputStream on a separate thread! Do NOT multithread I/O! Edit 2 I suppose I/O is the bottleneck, as I'm reading and writing to the same disk... In general, though, is there a way to make GZIPInputStream faster? Or a replacement for GZIPInputStream that runs parallel? Edit 3 Code snippet I used: GZIPInputStream gzip = new GZIPInputStream(new FileInputStream(INPUT_FILENAME)); DataInputStream in = new DataInputStream(new BufferedInputStream(gzip));

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  • Casting to generic type in Java doesn't raise ClassCastException?

    - by Kip
    I have come across a strange behavior of Java that seems like a bug. Is it? Casting an Object to a generic type (say, K) does not throw a ClassCastException even if the object is not an instance of K. Here is an example: import java.util.*; public final class Test { private static<K,V> void addToMap(Map<K,V> map, Object ... vals) { for(int i = 0; i < vals.length; i += 2) map.put((K)vals[i], (V)vals[i+1]); //Never throws ClassCastException! } public static void main(String[] args) { Map<String,Integer> m = new HashMap<String,Integer>(); addToMap(m, "hello", "world"); //No exception System.out.println(m.get("hello")); //Prints "world", which is NOT an Integer!! } }

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  • Swing: what to do when a JTree update takes too long and freezes other GUI elements?

    - by java.is.for.desktop
    Hello, everyone! I know that GUI code in Java Swing must be put inside SwingUtilities.invokeAndWait or SwingUtilities.invokeLater. This way threading works fine. Sadly, in my situation, the GUI update it that thing which takes much longer than background thread(s). More specific: I update a JTree with about just 400 entries, nesting depth is maximum 4, so should be nothing scary, right? But it takes sometimes one second! I need to ensure that the user is able to type in a JTextPane without delays. Well, guess what, the slow JTree updates do cause delays for JTextPane during input. It refreshes only as soon as the tree gets updated. I am using Netbeans and know empirically that a Java app can update lots of information without freezing the rest of the UI. How can it be done? NOTE 1: All those DefaultMutableTreeNodes are prepared outside the invokeAndWait. NOTE 2: When I replace invokeAndWait with invokeLater the tree doesn't get updated. NOTE 3: Fond out that recursive tree expansion takes far the most time. NOTE 4: I'm using custom tree cell renderer, will try without and report. NOTE 4a: My tree cell renderer uses a map to cache and reuse created JTextComponents, depending on tree node (as a key). CLUE 1: Wow! Without setting custom cell renderer it's 10 times faster. I think, I'll need few good tutorials on writing custom tree cell renderers.

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  • What XSLT processor should I use for Java transformation?

    - by Artic
    What XSLT processor should I use for Java transformation? There are SAXON, Xalan and TrAX. What is the criteria for my choice? I need simple transformation without complicated logical transformations. Need fast and easy to implement solution. APP runs under Tomcat, Java 1.5. I have some jaxp libraries and could not understand what is the version of jaxp used. Thanks in advance. Best regards.

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  • Is there Java counterpart for Aspnet 4's <%: %> XSS prevention?

    - by Tomas Tintera
    I'm developer moving from C# to Java. Heard about new ASP net feature. <%: %. It renders object with html encoding. Only these impolementing IHtmlString interface are not encoded (to prevent double encoding). See more in http://weblogs.asp.net/scottgu/archive/2010/04/06/new-lt-gt-syntax-for-html-encoding-output-in-asp-net-4-and-asp-net-mvc-2.aspx Is such cute tool in Java side? I mean a way to output a string to webpage and (not)encode it based on it's type.

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  • how to create an excel file in google app engine (java)?

    - by Joseph
    A question that seems to have quite a few options for Python, but none for Java after googling for two days. Really really could use some help all I have found so far is a recommendation to use gaeVFS to build an excel file from the xml components and then zip it all together which sounds like a slap in the face. Oh yes and if you were wondering I am questioning my use of Java rather than python but at 5,000 lines of code it would be insane to turn back now... Other things you might find useful Client: GWT Server: Servlets running on google app engine storing data into the google data store Excel file: mandatory, CSV isn't good enough, no need to save the file just to be able to "serve" it to the client i.e. open a "Save As" box.

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  • How do I call overloaded Java methods in Clojure.

    - by Pat Wallace
    For this example Java class: package foo; public class TestInterop { public String test(int i) { return "Test(int)"; } public String test(Object i) { return "Test(Object)"; } } When I start Clojure and try to call the test(int) method, the test(Object) method is called instead, because Clojure automatically boxes the integer into a java.lang.Integer object. How do I force Clojure to call the test(int) method? user=> (.test (new foo.TestInterop) 10) "Test(Object)" I want to call methods like Component.add(Component comp, int index) in AWT, but instead keep calling add(Component comp, Object constraints), so the buttons on my toolbar always appear in the wrong order.

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  • Is there a Java Package for testing RESTful APIs?

    - by Zachary Spencer
    I'm getting ready to dive into testing of a RESTful service. The majority of our systems are built in Java and Eclipse, so I'm hoping to stay there. I've already found rest-client (http://code.google.com/p/rest-client/) for doing manual and exploratory testing, but is there a stack of java classes that may make my life easier? I'm using testNG for the test platform, but would love helper libraries that can save me time. I've found http4e (http://www.ywebb.com/) but I'd really like something FOSS.

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  • How should I store an Java Enum in JavaDB?

    - by Jonas
    How should I store an Java Enum in JavaDB? Should I try to map the enums to SMALLINT and keep the values in source code only? The embedded database is only used by a single application. Or should I just store the values as DECIMAL? None of these solutions feels good/robust for me. Is there any better alternatives? Here is my enum: import java.math.BigDecimal; public enum Vat { NORMAL(new BigDecimal("0.25")), FOOD(new BigDecimal("0.12")), BOOKS(new BigDecimal("0.06")), NONE(new BigDecimal("0.00")); private final BigDecimal value; Vat(BigDecimal val) { value = val; } public BigDecimal getValue() { return value; } } I have read other similar questions on this topic, but the problem or solution doesn't match my problem. Enum storage in Database field, Best method to store Enum in Database, Best way to store enum values in database - String or Int

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  • Do Eclipse's Refactoring Tools Violate The Java Language Specification?

    - by Tom Tresansky
    In Eclipse 3.5, say I have a package structure like this: tom.package1 tom.package1.packageA tom.package1.packageB if I right click on an the tom.package1 package and go to Refactor-Rename, an option "Rename subpackages" appears as a checkbox. If I select it, and then rename tom.package1 to tom.red my package structure ends up like this: tom.red tom.red.packageA tom.red.packageB Yet I hear that Java's packages are not hierarchical. The Java Tutorials back that up (see the section on Apparent Hierarchies of Packages). It certainly seems like Eclipse is treating packages as hierarchical in this case. I was curious why access specifiers couldn't allow/restrict access to "sub-packages" in a previous question because I KNEW I had seen "sub-packages" referenced somewhere before. So are Eclipse's refactoring tools intentionally misleading impressionable young minds by furthering the "sub-package" myth? Or am I misinterpreting something here?

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  • Java: omitting a data member from the equals method.

    - by cchampion
    public class GamePiece { public GamePiece(char cLetter, int nPointValue) { m_cLetter=cLetter; m_nPointValue=nPointValue; m_nTurnPlaced=0; //has not been placed on game board yet. } public char GetLetter() {return m_cLetter;} public int GetPointValue() {return m_nPointValue;} public int GetTurnPlaced() {return m_nTurnPlaced;} public void SetTurnPlaced(int nTurnPlaced) { m_nTurnPlaced=nTurnPlaced; } @Override public boolean equals(Object obj) { /*NOTE to keep this shorter I omitted some of the null checking and instanceof stuff. */ GamePiece other = (GamePiece) obj; //not case sensitive, and I don`t think we want it to be here. if(m_cLetter != other.m_cLetter) { return false; } if(m_nPointValue != other.m_nPointValue) { return false; } /* NOTICE! m_nPointValue purposely omitted. It does not affect hashcode or equals */ return true; } @Override public int hashCode() { /* NOTICE! m_nPointValue purposely omitted. It should not affect hashcode or equals */ final int prime = 41; return prime * (prime + m_nPointValue + m_cLetter); } private char m_cLetter; private int m_nPointValue; private int m_nTurnPlaced;//turn which the game piece was placed on the game board. Does not affect equals or has code! } Consider the given piece of code. This object has been immutable until the introduction of the m_nTurnPlaced member (which can be modified by the SetTurnPlaced method, so now GamePiece becomes mutable). GamePiece is used in an ArrayList, I call contains and remove methods which both rely on the equals method to be implemented. My question is this, is it ok or common practice in Java for some members to not affect equals and hashcode? How will this affect its use in my ArrayList? What type of java Collections would it NOT be safe to use this object now that it is mutable? I've been told that you're not supposed to override equals on mutable objects because it causes some collections to behave "strangely" (I read that somewhere in the java documentation).

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  • Using the stadard Java logging, is it possible to restart logs after a certain period?

    - by Fry
    I have some java code that will be running as an importer for data for a much larger project. The initial logging code was done with the java.util.logging classes, so I'd like to keep it if possible, but it seems to be a little inadequate now given he amount of data passing through the importer. Often times in the system, the importer will get data that the main system doesn't have information for or doesn't match the system's data so it is ignored but a message is written to the log about what information was dropped and why it wasn't imported. The problem is that this tends to grow in size very quickly, so we'd like to be able to start a fresh log daily or weekly. Does anybody have an idea if this can be done in the logging classes or would I have to switch to log4j or custom? Thanks for any help!

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  • How can I easily make a java application invisible to the user?

    - by Pedro Bellora
    Hello! I have developed a Java aplication that is currently being run by double-clicking on a ".bat" file that does something like "java -jar proy.jar". This application just listens on a port and writes to a database, so it does not have any user interface (such as a window). I need this application to run as in background mode, or as it where a service, but I don't really anything more than that. It's enough if the application is run in a way that is not noticeable by the user, so that the user is not bothered and so the application can not be mistakenly closed. By the way, this will be run on an specific computer so it's okay if I have to do any manual configuration ir order to make this work. Also, I need this application to run on startup. Any help/tips regarding this? In advance, thank you very much for your help! Regards, Pedro

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  • Pure Java open-source libraries for portfolio selection (= constrained, non-linear optimization)?

    - by __roland__
    Does anyone know or has experience with a pure Java library to select portfolios or do some similar kinds of quadratic programming with constraints? There seems to be a lot of tools, as already discussed elsewhere - but what I would like to use is a pure Java implementation. Since I want to call the library from within another open-source software with a BSD-ish license I would prefer LGPL over GPL. Any help is appreciated. If you don't know such libraries, which is the most simple algorithm you would suggest to implement? It has to cope with an inequality constraint (all x_i = 0) and an equality constraint (sum of all x_i = 1).

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  • How to save, retrieve and draw an image in webapplication using Java and PostgreSQL?

    - by spderosso
    Given an object X; I want this object to have an image. The image must be stored in the database. I can't store the path, the actual image must be in the database. My question can be answered by answering the following subquestions: a). What type of field should I put in the database? (e.g VARCHAR) b) What type of object should I use for storing and manipulating the image (at an object layer)? (e.g java.awt.Image) c) How do I create an object of the type selected (answer of question b) from the data obtained from the database? d) How do I save an object of the type selected (answer of question b) to the database? e) How do I draw the image on a web page? I am using PostgreSQL, Java and it is a web application. Thanks!

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  • Custom Java events with listeners vs. a JMS based implementation?

    - by Joe Dean
    My application requires events to be fired based on some specific activities that happen. I'm trying to determine if I should create my own event handling system using the Java EventObject with custom listeners similar to Java AWT Or should I use a JMS implementation? I was considering either apache's Qpid or ActiveMQ solution. I'm exploring these options at the moment and was wondering if anyone has experience with Qpid or ActiveMQ and can offer some advise (e.g., pros, cons to consider, etc) Also, if anyone has any suggestions for building a simple event handling system... if it's even worth while to consider this over a JMS based solution.

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