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  • What can you do in the ant Task.init() method?

    - by skiphoppy
    I'm developing a few custom ant tasks that all need to initialize the same objects. I wanted to initialize those object's in a common superclass that extends from Task, in the init() method. But I see from the lifecycle of an ant task that init() gets called before the tasks child elements and attributes are set. So all of the data I need for initializing those objects is unavailable during init(), if I am reading right. So, why is init() called at this point? What do you even know that you could use in init()? What could it be used for? (And is there some other method that I can rely on to be called before execute(), but after my data is available?)

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  • Making an efficient algorithm

    - by James P.
    Here's my recent submission for the FB programming contest (qualifying round only requires to upload program output so source code doesn't matter). The objective is to find two squares that add up to a given value. I've left it as it is as an example. It does the job but is too slow for my liking. Here's the points that are obviously eating up time: List of squares is being recalculated for each call of getNumOfDoubleSquares(). This could be precalculated or extended when needed. Both squares are being checked for when it is only necessary to check for one (complements). There might be a more efficient way than a double-nested loop to find pairs. Other suggestions? Besides this particular problem, what do you look for when optimizing an algorithm? public static int getNumOfDoubleSquares( Integer target ){ int num = 0; ArrayList<Integer> squares = new ArrayList<Integer>(); ArrayList<Integer> found = new ArrayList<Integer>(); int squareValue = 0; for( int j=0; squareValue<=target; j++ ){ squares.add(j, squareValue); squareValue = (int)Math.pow(j+1,2); } int squareSum = 0; System.out.println( "Target=" + target ); for( int i = 0; i < squares.size(); i++ ){ int square1 = squares.get(i); for( int j = 0; j < squares.size(); j++ ){ int square2 = squares.get(j); squareSum = square1 + square2; if( squareSum == target && !found.contains( square1 ) && !found.contains( square2 ) ){ found.add(square1); found.add(square2); System.out.println( "Found !" + square1 +"+"+ square2 +"="+ squareSum); num++; } } } return num; }

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  • What is the effect of final variable declaration in methods?

    - by Finbarr
    Classic example of a simple server: class ThreadPerTaskSocketServer { public static void main(String[] args) throws IOException { ServerSocket socket = new ServerSocket(80); while (true) { final Socket connection = socket.accept(); Runnable task = new Runnable() { public void run() { handleRequest(connection); } }; new Thread(task).start(); } } } Why should the Socket be declared as final? Is it because the new Thread that handles the request could refer back to the socket variable in the method and cause some sort of ConcurrentModificationException?

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  • Why does the Maven goal "package" include the resources in the jar, but the goal "jar:jar" doesnt?

    - by Bernhard V
    Hi, when I package my project with the Maven goal "package", the resources are included as well. They are originally located in the directory "src/main/resources". Because I want to create an executable jar and add the classpath to the manifest, I'm using maven-jar-plugin. I've configured it as the following likes: <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-jar-plugin</artifactId> <version>2.2</version> <configuration> <archive> <manifest> <addClasspath>true</addClasspath> <mainClass>at.sozvers.stp.zpv.ekvkumsetzer.Main</mainClass> </manifest> </archive> </configuration> </plugin> Why won't the jar file created with "jar:jar" include my resources as well. As far as I'm concerned it should use the same directories as the "package" goal (which are in my case inherited from the Maven Super POM).

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  • Set reference = null in finally block?

    - by deamon
    A colleague of mine sets reference to null in finally blocks. I think this is nonsense. public Something getSomething() { JDBCConnection jdbc=null; try { jdbc=JDBCManager.getConnection(JDBCTypes.MYSQL); } finally { JDBCManager.free(jdbc); jdbc=null; // <-- Useful or not? } } What do you think of it?

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  • runtime/compile time polymorphism

    - by dmadhavaraj
    Hi , In the below code , why b1.subtract() fails . Please explain me the reason ie., what happens in JVM while invoking that method . class Base { public void add() { System.out.println("Base ADD"); } } class Child extends Base { public void add(){ System.out.println("Child ADD"); } public void subtract() { System.out.println("Child Subtract"); } } class MainClass { public static void main(String args[]) { Base b1 = new Base(); Base b2 = new Child(); Child b3 = new Child(); b1.add(); b1.subtract(); // ?????????** b2.add(); b3.subtract(); } }

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  • Annotations: methods vs variables

    - by Zenzen
    I was always sure (don't know why) that it's better to add annotations to variables, but while browsing the Hibernate doc http://docs.jboss.org/hibernate/stable/annotations/reference/en/html_single/#entity-hibspec-collection I noticed they tend to annotate the methods. So should I put my annotations before methods, like this: @Entity public class Flight implements Serializable { private long id; @Id @GeneratedValue public long getId() { return id; } public void setId(long id) { this.id = id; } } Or is it better to do it like this: @Entity public class Flight implements Serializable { @Id @GeneratedValue private long id; public long getId() { return id; } public void setId(long id) { this.id = id; } } Or maybe there's no difference?

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  • How to embed revision information using mercurial and maven (and svn)

    - by Zwei Steinen
    Our project had a nice hack (although I'm guessing there are better ways to do it) to embed revision information into the artifacts (jar etc.) when we used svn. Now we have migrated to mercurial, and we want to have a similar thing, but before I start working on a similar hack with mercurial, I wanted to know if there are better ways to do this. Thanks for your answers! <plugin> <groupId>org.codehaus.mojo</groupId> <artifactId>exec-maven-plugin</artifactId> <executions> <execution> <phase>process-classes</phase> <id>svninfo</id> <goals> <goal>exec</goal> </goals> <configuration> <executable>svn</executable> <arguments> <argument>info</argument> <argument>../</argument> <argument>></argument> <argument>target/some-project/META-INF/svninfo.txt</argument> </arguments> </configuration> </execution> </executions> </plugin>

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  • Spring Framework HttpRequestHandler failure

    - by sharadva
    We have an application which communicates via REST requests made by clients. The REST requests contain "region name" and a "ID" as parameters So, a request would look something like this (for a DELETE) http://host:port/regionnameID These REST requests between regions in a federation are properly URL encoded I find that these request fail if the region name has a slash ("/") in it. Then, the request would look like so http://host:port/region/nameID This is due to incorrect interpretation of the Rest URL by HttpRequesthandler when there is a '/' in the region name. Now, we have no control over clients sending REST request with "/" in the Region name. Is there any method / configuration / workaround that can be done to prevent the HttpRequestHandler from returning 404

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  • Direct flow depending on incoming dynamic type

    - by Improfane
    I have a listener class that accepts GUI change events in one method. The incoming event objects have a superclass of a type of GUI Event, the behaviour should depend on the dynamic type of the incoming variable. I wanted to do do lots of methods like: handleGUIEvent(EventChangedX event) handleGUIEvent(EventChangedY event) I am using a single event listener and receiving objects of various types but the behaviour should be different for each. What would you do? I do not want to use a switch statement as this would get unmaintainable.

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  • BeanUtils getPropertyOfMapBean

    - by dx-cp
    Hi, Im wondering if it is possible to get data from property which is map cotaining pairs Key-StringArray (Map) in BeanUtils library. I just simply need to access one of array elements by calling propertyName=string[0]. Current version (1.8.3) does not support indexed properties. If you look into their code you will find in class PropertyUtilsBean in method getPropertyOfMapBean: if (resolver.isIndexed(propertyName) || resolver.isMapped(propertyName)) { throw new IllegalArgumentException( "Indexed or mapped properties are not supported on" + " objects of type Map: " + propertyName); } way too bad:-( Have any of you any tip how to do it somehow differently?

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  • Testing a quadratic equation

    - by user1201587
    I'm doing a code testing for a program that calculate the results for a quadratic equation I need to have test data for the following situation, when a is not zero and d positive there is two possibilities which are in the code below, I need to find an example for the first satiation when Math.abs(b / a - 200.0) < 1.0e-4 , all the values that I have tried, excute the second one caption= "Two roots"; if (Math.abs(b / a - 200.0) < 1.0e-4) { System.out.println("first one"); x1 = (-100.0 * (1.0 + Math.sqrt(1.0 - 1.0 / (10000.0 * a)))); x2 = (-100.0 * (1.0 - Math.sqrt(1.0 - 1.0 / (10000.0 * a)))); } else { System.out.println("secrst one"); x1 = (-b - Math.sqrt(d)) / (2.0 * a); x2 = (-b + Math.sqrt(d)) / (2.0 * a); } } }

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  • Can Spring understand @Inject replacing Weld as a JSR-299 implementation?

    - by Thorbjørn Ravn Andersen
    I have noticed from several web pages that apparently Spring 3.0 supports @Inject from JSR-330. As we would really like to use JSR-299 syntax for dependency injection in our libraries for both web apps and stand-alone applications, and have alternatives to Weld, it would be nice if Spring could do this. Being a novice to Spring, I tried downloading the Spring Framework distribution and put all jars on the Eclipse build path. No Inject annotation so my existing test project using Weld did not compile. Can this be done with Spring? What do I need to do to get it running? (I am aware that Guice eventually will support this too. It is only in SVN for now, and if there is an official Spring release which can, that would be better.)

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  • problem with update the counter value

    - by Edan
    Hello, I having problem to update the counter (integer value). this is the definitions of the class: public class Item_Actions { private final int MAX_ITEMS = 100; private Item myItem[]; private int counter; public Item_Actions() { myItem = new Item[MAX_ITEMS]; counter++; } //Constructor add item into the menu (Description, type & price of Item) public void addItem(Item itm) { myItem[counter] = itm; counter++; }....... Now everytime I call the addItem constructor from another class, the counter always stays on zero. What causing it and how do I save the data inside? thanks

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  • Is it possible to start an activity in a different apk using startActivity on Android using the acti

    - by icecream
    I have tried to write an Android application with an activity that should be launched from a different application. It is not a content provider, just an app with a gui that should not be listed among the installed applications. I have tried the code examples here and it seems to be quite easy to launch existing providers and so on, but I fail to figure out how to just write a "hidden" app and launch it from a different one. The basic use case is: App A is a normal apk launchable from the application list. App B is a different apk with known package and activity names, but is is not visible or launchable from the application list. App A launches app B using the package and class names (or perhaps a URI constructed from these?). I fail in the third step. Is it possible to do this?

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  • task strategies for handling HardDeadlineExceededError

    - by Stevko
    I've got a number of tasks/servlets that are hitting the HardDeadlineExceededError which is leaving everything hanging in an 'still executing' state. The work being done can easily exceed the 29 second threshold. I try to catch the DeadlineExceededException and base Exception in order to save the exit state but neither of these exception handlers are being caught... Is there a way to determine which tasks are in the queue or currently executing? Are there any other strategies for dealing with this situation?

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  • Reading a simple Avro file from HDFS

    - by John Galt... who
    I am trying to do a simple read of an Avro file stored in HDFS. I found out how to read it when it is on the local file system.... FileReader reader = DataFileReader.openReader(new File(filename), new GenericDatumReader()); for (GenericRecord datum : fileReader) { String value = datum.get(1).toString(); System.out.println("value = " value); } reader.close(); My file is in HDFS, however. I cannot give the openReader a Path or an FSDataInputStream. How can I simply read an Avro file in HDFS? EDIT: I got this to work by creating a custom class (SeekableHadoopInput) that implements SeekableInput. I "stole" this from "Ganglion" on github. Still, seems like there would be a Hadoop/Avro integration path for this. Thanks

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  • Common Utility for Exception Searching

    - by Andrew
    I wrote this little helper method to search the exception chain for a particular exception (either equals or super class). However, this seems like a solution to a common problem, so was thinking it must already exist somewhere, possibly in a library I have already imported. So, any ideas on if/where this might exist? boolean exceptionSearch(Exception base, Class<?> search) { Throwable e = base; do { if (search.isAssignableFrom(e.getClass())) { return true; } } while ((e = e.getCause()) != null); return false; }

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  • Set request attributes when a Form is POSTed

    - by ssahmed555
    Is there any way to set request attributes (not parameters) when a form is posted? The problem I am trying to solve is: I have a JSP page displaying some data in a couple of dropdown lists. When the form is posted, my Controller servlet processes this request (based on the parameters set/specified in the form) and redirects to the same JSP page that is supposed to display addition details. I now want to display the same/earlier data in the dropdown lists without having to recompute or recalculate to get that same data. And in the said JSP page, the dropdown lists in the form are populated by data that is specified through request attributes. Right now, after the Form is POSTed and I am redirected to the same JSP page the dropdown lists are empty because the necessary request attributes are not present. I am quite the n00b when it comes to web apps, so an obvious & easy solution to this problem escapes me at the moment! I am open to suggestions on how to restructure the control flow in the Servlet. Some details about this app: standard Servlet + JSP, JSTL, running in Apache Tomcat 6.0. Thanks.

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  • Free JVM profilers for websites

    - by 2Real
    I'm looking for a JVM profiler (preferably open source) so I can look at the heap and cpu usage of my personal website. I've used Lambda Probe, and I like it because it provides a web interface for my remote Unix computer that has no display. I was wondering what else is available Thanks,

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  • Trimmed down JAXB for just unmarshalling?

    - by fiXedd
    I'm building an application where space is at a premium. I'd really like to use JAXB's unmarshalling capabilities, but including the whole library is out of the question. Has anyone paired it down so that only the bits needed for unmarshalling are included?

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