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  • Getting a cryptic error on my simple Java program, comparing char[i] to a string.

    - by Sergio Tapia
    public static void ejemplosString(String palabra){ char[] letras = palabra.toCharArray(); int contadorVocales = 0; for (int i = 0; i < letras.length; i++) { if (char[i] == 'a') { contadorVocales++; } if (char[i] == "e") { contadorVocales++; } if (char[i] == "i") { contadorVocales++; } if (char[i] == "o") { contadorVocales++; } if (char[i] == "u") { contadorVocales++; } } } Getting the error on every If statement. Any guidance?

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  • Creating lib file from java jar using mingw/gcj

    - by Xinus
    I am trying to convert jar file to native lib file using mingw-gcj under windows platform it is thrown me the error as C:\testDir\libs>gcj -o glassfish-embedded-all-3.1-SNAPSHOT.lib glassfish-embedde d-all-3.1-SNAPSHOT.jar com/sun/codemodel/JAnonymousClass.java: In class 'com.sun.codemodel.JAnonymousCl ass': com/sun/codemodel/JAnonymousClass.java: In constructor '(com.sun.codemodel.JClas s,com.sun.codemodel.JCodeModel)': In file included from com/sun/codemodel/CodeWriter.java:15, from <built-in>:3: com/sun/codemodel/JAnonymousClass.java:21: error: verification failed at PC=3: c onstant pool index out of range com/sun/codemodel/JAnonymousClass.java:21: confused by earlier errors, bailing o ut Is it related to some java 1.6 issue or bug in gcj /

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  • How do you raise a Java BigInteger to the power of a BigInteger without doing modular arithmetic?

    - by angstrom91
    I'm doing some large integer computing, and I need to raise a BigInteger to the power of another BigInteger. The .pow() method does what I want, but takes an int value as an argument. The .modPow method takes a BigInteger as an argument, but I do not want an answer congruent to the value I'm trying to compute. My BigInteger exponent is too large to be represented as an int, can someone suggest a way to work around this limitation?

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  • Java - How to declare table[i][j] elements as instance variables?

    - by JDelage
    All, I am trying to code a Connect4 game. For this, I have created a P4Game class and a P4Board class which represents the i X j dimensions of the Connect4 board. In P4Game, I have the following: public class P4Game{ //INSTANCE VARIABLES private int nbLines; private int nbColumns; private P4Board [][] position; //CONSTRUCTOR public P4Game(int nbLines, int nbColumns){ this.nbColumns = nbColumns; this.nbLines = nbLines; P4Board [][] position = new P4Board [nbLines][nbColumns]; //Creates the table to receive the instances of the P4Board object.*/ for (int i=0; i<nbLines; i++){ for (int j=0; j<nbColumns; j++){ this.position[i][j] = new P4Board(i,j); //Meant to create each object at (line=i, column=j) } } } This causes a NullPointerException in the nested loops where I mention this.position[i][j]. I reference those objects in other methods of this class so I need them to be instance variables. I suppose the exception is due to the fact that I have not listed the table element position[i][j] as an instance variable at the beginning of the class. my question to people here is (1) is my assumption correct, and if so (2) what would be the syntax to declare instance variables of this form? Thank you all for your help with what I realize is a very basic question. Hopefully it will also benefit other newbies. Cheers, JDelage

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  • Java Swing: how to listen to JComboBox's width changes?

    - by agnieszka
    I tried PropertyChangeListener with property set to "width", "Width", "size" and "Size". PropertyChangeListener widthChangeListener = new PropertyChangeListener() { @Override public void propertyChange(PropertyChangeEvent evt) { //code } }; streamsComboBox.addPropertyChangeListener("width", widthChangeListener); projectsComboBox.addPropertyChangeListener("width", widthChangeListener); vobsComboBox.addPropertyChangeListener("width", widthChangeListener); Nothing works - the handler method is never fired. What should I do to handle JComboBox's size change? Where does the property name come from anyway?

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  • Pass in the object a java class is embedded in as a parameter.

    - by Leif Andersen
    I'm building an android application, which has a list view, and in the list view, a click listener, containing an onItemClick method. So I have something like this: public class myList extends ListActivity { @Override public void onCreate(Bundle savedInstanceState) { getListView().setOnItemClickListener(new OnItemClickListener() { public void onItemClick(AdapterView<?> parent, View view, int position, long id) { /* Do something*/ } } } Normally, this works fine. However, many times I find myself needing too preform an application using the outer class as a context. thusfar, I've used: parent.getContext(); to do this, but I would like to know, is that a bad idea? I can't really call: super because it's not really a subclass, just an embedded one. So is there any better way, or is that considered cosure? Also, if it is the right way, what should I do if the embedded method doesn't have a parameter to get the outside class? Thank you.

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  • java methods and race condition in a jsp/servlets application.

    - by A.S al-shammari
    Hi. Suppose that I have a method called doSomething() and I want to use this method in a multithreaded application (each servlet inherits from HttpServlet).I'm wondering if it is possible that a race condition will occur in the following cases: doSomething() is not staic method and it writes values to a database. doSomething() is static method but it does not write values to a database. what I have noticed that many methods in my application may lead to a race condition or dirty read/write. for example , I have a Poll System , and for each voting operation, a certain method will change a single cell value for that poll as the following: [poll_id | poll_data ] [1 | {choice_1 : 10, choice_2 : 20}] will the JSP/Servlets app solve these issues by itself, or I have to solve all that by myself? Thanks..

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  • Straight Java/Groovy versus ETL tool (Talend/etc) - what libraries would you use?

    - by Alex R
    Assume you have a small project which on the surface looks like a good match for an ETL tool like Talend. But assume further, that you have never used Talend and furthermore, you do not trust "visual programming" tools in general and would rather code everything the old fashioned way (text on a nice IDE!) with the help of an appropriate language & support libraries. What are some language patterns & support libraries that could help you stay away from the ETL tool temptation/trap?

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  • Java: How to test methods that call System.exit()?

    - by Chris Conway
    I've got a few methods that should call System.exit() on certain inputs. Unfortunately, testing these cases causes JUnit to terminate! Putting the method calls in a new Thread doesn't seem to help, since System.exit() terminates the JVM, not just the current thread. Are there any common patterns for dealing with this? For example, can I subsitute a stub for System.exit()? [EDIT] The class in question is actually a command-line tool which I'm attempting to test inside JUnit. Maybe JUnit is simply not the right tool for the job? Suggestions for complementary regression testing tools are welcome (preferably something that integrates well with JUnit and EclEmma).

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  • Java - How to force resize JCheckBox to prevent clicking the empty space ?

    - by Brad
    When i create a JCheckBox in my Swing application i leave some extra space after its label, so if the JCheckBox label is for example 100 pixels width, i make the JCheckBox 120 pixels for safety. The problem as at runtime, it's not nice that a user can click on the empty space after the JCheckBox label and it can be actually clicked, like this : I wonder if there is a way to resize the JCheckBox at runtime to exactly fit the text inside it, depending on the font type/size used ? This seems fancy a bit, but i like to make things look perfect :)

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  • When does the call() method get called in a Java Executor using Callable objects?

    - by MalcomTucker
    This is some sample code from an example. What I need to know is when call() gets called on the callable? What triggers it? public class CallableExample { public static class WordLengthCallable implements Callable { private String word; public WordLengthCallable(String word) { this.word = word; } public Integer call() { return Integer.valueOf(word.length()); } } public static void main(String args[]) throws Exception { ExecutorService pool = Executors.newFixedThreadPool(3); Set<Future<Integer>> set = new HashSet<Future<Integer>>(); for (String word: args) { Callable<Integer> callable = new WordLengthCallable(word); Future<Integer> future = pool.submit(callable); //**DOES THIS CALL call()?** set.add(future); } int sum = 0; for (Future<Integer> future : set) { sum += future.get();//**OR DOES THIS CALL call()?** } System.out.printf("The sum of lengths is %s%n", sum); System.exit(sum); } }

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  • java - how to split string in to multiple parts?

    - by Ewen
    I have a string that contains a value "firstword second third", and an ArrayList. I want to split the whole string in to by spaces and add the splitted strings in to the ArrayList. For example,"firstword second third" can be split to three separate strings and added three times in to the ArrayList. "1 2 3 4" can be splitted in to 4 strings and added 4 times in to the ArrayList. See the code below: public void separateAndAdd(String notseparated) { for(int i=0;i<canBeSepartedinto(notseparated);i++{ //what should i put here in order to split the string via spaces? thearray.add(separatedstring); } } public int canBeSeparatedinto(String string) //what do i put here to find out the amount of spaces inside the string? return .... } Please leave a comment if you dont get what I mean or I should fix some errors in this post. Thanks for your time!

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  • How can I rotate an image using Java/Swing and then set its origin to 0,0?

    - by JT
    I'm able to rotate an image that has been added to a JLabel. The only problem is that if the height and width are not equal, the rotated image will no longer appear at the JLabel's origin (0,0). Here's what I'm doing. I've also tried using AffineTransform and rotating the image itself, but with the same results. Graphics2D g2d = (Graphics2D)g; g2d.rotate(Math.toRadians(90), image.getWidth()/2, image.getHeight()/2); super.paintComponent(g2d); If I have an image whose width is greater than its height, rotating that image using this method and then painting it will result in the image being painted vertically above the point 0,0, and horizontally to the right of the point 0,0.

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  • JAVA: 500 Worker Threads, what kind of thread pool?

    - by Submerged
    I am wondering if this is the best way to do this. I have about 500 threads that run indefinitely, but Thread.sleep for a minute when done one cycle of processing. ExecutorService es = Executors.newFixedThreadPool(list.size()+1); for (int i = 0; i < list.size(); i++) { es.execute(coreAppVector.elementAt(i)); //coreAppVector is a vector of extends thread objects } I do need a separate threads for each running task, so changing the architecture isn't an option. I tried making my threadPool size equal to Runtime.getRuntime().availableProcessors() which attempted to run all 500 threads, but only let 8 (4xhyperthreading) of them execute. The other threads wouldn't surrender and let other threads have their turn. I tried putting in a wait() and notify(), but still no luck. If anyone has a simple example or some tips, I would be grateful!

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  • How to (simply) create new service objects in java jax-ws webservices?

    - by cibercitizen1
    Is it possible in jax-ws to have a webmethod that creates a new object (of a service class) and returns a reference to it to the client caller (for the client, it's a remote reference) so that the client and this new service object maintain a session? (Therefore each client is served by a different instance). Schematically: client server o:Session -------- -------- ---------- s = server.access() ------------------> o = new Session() return o <--- o.doSomething() ----------------------------------------------> make it <--- o.doMore() --------------------------------------------------> make it <---

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  • Is it bad to explicitly compare against boolean constants e.g. if (b == false) in Java?

    - by polygenelubricants
    Is it bad to write: if (b == false) //... while (b != true) //... Is it always better to instead write: if (!b) //... while (!b) //... Presumably there is no difference in performance (or is there?), but how do you weigh the explicitness, the conciseness, the clarity, the readability, etc between the two? Note: the variable name b is just used as an example, ala foo and bar.

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