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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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  • 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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  • Why is my program freezing when I use a method? (Java)

    - by user2915567
    When I use a boolean method in the Main body, my program freezes and stops working. I've tried putting the method at different places but the exact same thing happens - it freezes. The method is really simple and well-written, I'm not sure what's causing the problem. P.S. The method is on the bottom of the code. Thanks for your help! Edit: That was a dumb question now that I look at it. Thanks again everyone! public static void main(String[] args) { Scanner keyboard = new Scanner(System.in); int stringNumber = 0; String[] stringArray = new String[10]; for (int i = 0; i <= stringArray.length; i++) { boolean itemExists = false; boolean AddItem = AddItem(); if (AddItem == true) { out.println("\nEnter a string"); String input = keyboard.next(); if (i > 0) { for (int j = 0; j < stringArray.length; j++) { if (input.equalsIgnoreCase(stringArray[j])) { itemExists = true; out.println("Item \"" + input + "\" already exists."); break; } } } if (itemExists == false) { stringArray[stringNumber] = input; out.println("\"" + stringArray[stringNumber] + "\"" + " has been stored.\n"); } else { out.println("Try again."); i--; } PrintArray(stringArray); stringNumber++; } } } // This is the method I was talking about // public static boolean AddItem() { Scanner keyboard = new Scanner(System.in); int input = keyboard.nextInt(); out.println("If you want to add an item, Press 1"); if (input == 1) { return true; } else { out.println("Invalid input."); return false; } }

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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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  • Java - Adding a Node in a doubly-linked list.

    - by jacobnlsn
    Hi, I am working on some code were I need to add a Node into a doubly linked-list, this is the code I have so far: Node tempNext = cursor.getNext(); temp = new Node(item, null, cursor, tempNext); tempNext.setPrev(temp); cursor is the Node that is right before the new added Node should go.

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  • Java HashSet is allowing dupes; problem with comparable?

    - by IVR Avenger
    Hi, all. I've got a class, "Accumulator", that implements the Comparable compareTo method, and I'm trying to put these objects into a HashSet. When I add() to the HashSet, I don't see any activity in my compareTo method in the debugger, regardless of where I set my breakpoints. Additionally, when I'm done with the add()s, I see several duplicates within the Set. What am I screwing up, here; why is it not Comparing, and therefore, allowing the dupes? Thanks, IVR Avenger

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  • What's the best way to keep java app data stored redundantly in a file?

    - by Bijan
    If I have systems that are based on realtime data, how can I ensure that all the information that is current is redundantly stored in a file? So that when the program starts again, it uses this information to initialize itself back to where it was when it closed. I know of xstream and HSQLDB. but wasn't sure if this was the best option for data that needs to be a literal carbon copy.

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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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  • Array inside of Arrays; Java (Help with Lab Assignment)

    - by Adam
    We are working on a lab assignment for my CS&E class and I think I can ask this question without going into detail of the entire lab requirements, but is it possible for an array to be inside of an array? For example, would this work: int [] arrayOne = new int[3]; arrayOne[0] = Start of an array If this is possible how do you go about doing it?

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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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  • What's a reasonable way to mutate a primitive variable from an anonymous Java class?

    - by Steve
    I would like to write the following code: boolean found = false; search(new SearchCallback() { @Override void onFound(Object o) { found = true; } }); Obviously this is not allowed, since found needs to be final. I can't make found a member field for thread-safety reasons. What is the best alternative? One workaround is to define final class MutableReference<T> { private T value; MutableReference(T value) { this.value = value; } T get() { return value; } void set(T value) { this.value = value; } } but this ends up taking a lot of space when formatted properly, and I'd rather not reinvent the wheel if at all possible. I could use a List<Boolean> with a single element (either mutating that element, or else emptying the list) or even a Boolean[1]. But everything seems to smell funny, since none of the options are being used as they were intended. What is a reasonable way to do this?

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  • Java: how do I get a class literal from a generic type?

    - by Tom
    Typically, I've seen people use the class literal like this: Class<Foo> cls = Foo.class; But what if the type is generic, e.g. List? This works fine, but has a warning since List should be parameterized: Class<List> cls = List.class So why not add a <?>? Well, this causes a type mismatch error: Class<List<?>> cls = List.class I figured something like this would work, but this is just a plain ol' a syntax error: Class<List<Foo>> cls = List<Foo>.class How can I get a Class<List<Foo>> statically, e.g. using the class literal? I could use @SuppressWarnings("unchecked") to get rid of the warnings caused by the non-parameterized use of List in the first example, Class<List> cls = List.class, but I'd rather not. Any suggestions? Thanks!

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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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  • Better Java method Syntax? Return early or late? [closed]

    - by Gandalf
    Duplicate: Should a function have only one return statement? and Single return or multiple return statements? Often times you might have a method that checks numerous conditions and returns a status (lets say boolean for now). Is it better to define a flag, set it during the method, and return it at the end : boolean validate(DomainObject o) { boolean valid = false; if (o.property == x) { valid = true; } else if (o.property2 == y) { valid = true; } ... return valid; } or is it better/more correct to simply return once you know the method's outcome? boolean validate(DomainObject o) { if (o.property == x) { return true; } else if (o.property2 == y) { return true; } ... return false; } Now obviously there could be try/catch blocks and all other kinds of conditions, but I think the concept is clear. Opinions?

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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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  • 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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