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  • Building "isolated" and "automatically updated" caches (java.util.List) in Java.

    - by Aidos
    Hi Guys, I am trying to write a framework which contains a lot of short-lived caches created from a long-living cache. These short-lived caches need to be able to return their entier contents, which is a clone from the original long-living cache. Effectively what I am trying to build is a level of transaction isolation for the short-lived caches. The user should be able to modify the contents of the short-lived cache, but changes to the long-living cache should not be propogated through (there is also a case where the changes should be pushed through, depending on the Cache type). I will do my best to try and explain: master-cache contains: [A,B,C,D,E,F] temporary-cache created with state [A,B,C,D,E,F] 1) temporary-cache adds item G: [A,B,C,D,E,F] 2) temporary-cache removes item B: [A,C,D,E,F] master-cache contains: [A,B,C,D,E,F] 3) master-cache adds items [X,Y,Z]: [A,B,C,D,E,F,X,Y,Z] temporary-cache contains: [A,C,D,E,F] Things get even harder when the values in the items can change and shouldn't always be updated (so I can't even share the underlying object instances, I need to use clones). I have implemented the simple approach of just creating a new instance of the List using the standard Collection constructor on ArrayList, however when you get out to about 200,000 items the system just runs out of memory. I know the value of 200,000 is excessive to iterate, but I am trying to stress my code a bit. I had thought that it might be able to somehow "proxy" the list, so the temporary-cache uses the master-cache, and stores all of it's changes (effectively a Memento for the change), however that quickly becomes a nightmare when you want to iterate the temporary-cache, or retrieve an item at a specific index. Also given that I want some modifications to the contents of the list to come through (depending on the type of the temporary-cache, whether it is "auto-update" or not) and I get completly out of my depth. Any pointers to techniques or data-structures or just general concepts to try and research will be greatly appreciated. Cheers, Aidos

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  • Enumeration classes in Java

    - by Crystal
    I have one class that declares an enumeration type as: public enum HOME_LOAN_TERMS {FIFTEEN_YEAR, THIRTY_YEAR}; Is this type usable in another class? I'm basically trying to complete a homework assignment where we have two types of loans, and one loanManager class. When I try to use the HOME_LOAN_TERMS.THIRTY_YEAR in my loanManager class that does not extend or implement the loan class, I get an error saying it 'cannot find symbol HOME_LOAN_TERMS.' So I did not know if my loanManager class needed to implement the two different loan classes. Thanks.

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  • Confusion in RegExp Reluctant quantifier? Java

    - by Dusk
    Hi, Could anyone please tell me the reason of getting an output as: ab for the following RegExp code using Relcutant quantifier? Pattern p = Pattern.compile("abc*?"); Matcher m = p.matcher("abcfoo"); while(m.find()) System.out.println(m.group()); // ab and getting empty indices for the following code? Pattern p = Pattern.compile(".*?"); Matcher m = p.matcher("abcfoo"); while(m.find()) System.out.println(m.group());

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  • Java generics question

    - by user247866
    So I have 3 classes. Abstract class A Class B extends class A independent Class C In class D that contains the main method, I create a list of instances of class B List<B> b = methodCall(); // the method returns a list of instances of class B Now in class C I have one method that is common to both A and B, and hence I don't want to duplicate it. I want to have one method that takes as input an instance of class A, as follows: public void someMethod(List<A> a) However, when I do: C c = new C(); c.someMethod(b); I get an error that some-method is not applicable for the argument List<B>, instead it's expecting to get List<A>. Is there a good way to fix this problem? Many thanks!

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  • Java Ugly Rounding Error?

    - by billynomates
    Using series.add(180, 1); produces a perfectly valid chart like this (little red dot at the bottom with some PolarItemRenderer Mods!) but using series.add(3000/(6000/360), 1); produces this beast: I assume it's because somewhere, 6000/360 = 16.6... is getting rounded? How can I stop this happening? Thanks :)

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  • Java - Need help with binary/code string manipulation

    - by ShrimpCrackers
    For a project, I have to convert a binary string into (an array of) bytes and write it out to a file in binary. Say that I have a sentence converted into a code string using a huffman encoding. For example, if the sentence was: "hello" h = 00 e = 01, l = 10, o = 11 Then the string representation would be 0001101011. How would I convert that into a byte? <-- If that question doesn't make sense it's because I know little about bits/byte bitwise shifting and all that has to do with manipulating 1's and 0's.

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  • How to keep Java Frame from waiting?

    - by pypmannetjies
    I am writing a genetic algorithm that approximates an image with a polygon. While going through the different generations, I'd like to output the progress to a JFrame. However, it seems like the JFrame waits until the GA's while loop finishes to display something. I don't believe it's a problem like repainting, since it eventually does display everything once the while loop exits. I want to GUI to update dynamically even when the while loop is running. Here is my code: while (some conditions) { //do some other stuff gui.displayPolygon(best); gui.displayFitness(fitness); gui.setVisible(true); } public void displayPolygon(Polygon poly) { BufferedImage bpoly = ImageProcessor.createImageFromPoly(poly); ImageProcessor.displayImage(bpoly, polyPanel); this.setVisible(true); } public static void displayImage(BufferedImage bimg, JPanel panel) { panel.removeAll(); panel.setBounds(0, 0, bimg.getWidth(), bimg.getHeight()); JImagePanel innerPanel = new JImagePanel(bimg, 25, 25); panel.add(innerPanel); innerPanel.setLocation(25, 25); innerPanel.setVisible(true); panel.setVisible(true); }

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  • How to rotate an image properly in JPanel (Java)

    - by Bruce
    Hi guys, I'm working on rotating a loaded image. I set the graphics on a JPanel and then use standard AffineTransform in order to rotate it, say, 45 degrees. Unfortunately, the image is being cut, if it exceeds the panel area. How may I force JPanel to add scrolls to itself (while loading an image file, I would like to adjust the size of JPanel by adding the scrolls, without adjusting the size of JFrame). Or, in other words, how to correctly rotate the whole image? Thank you in advance for the reply!

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  • java thread - run() and start() methods

    - by JavaUser
    Please explain the output of the below code: If I call th1.run() ,the output is EXTENDS RUN RUNNABLE RUN If I call th1.start() , the output is : RUNNABLE RUN EXTENDS RUN Why this inconsistency . Please explain. class ThreadExample extends Thread{ public void run(){ System.out.println("EXTENDS RUN"); } } class ThreadExampleRunnable implements Runnable { public void run(){ System.out.println("RUNNABLE RUN "); } } class ThreadExampleMain{ public static void main(String[] args){ ThreadExample th1 = new ThreadExample(); //th1.start(); th1.run(); ThreadExampleRunnable th2 = new ThreadExampleRunnable(); th2.run(); } }

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  • Java Programming Homework

    - by user1427476
    Write a program to read in a file containing the names of the employ of a company and store them in an array of Strings named Employ []. Read another file containing the Salaries of each employ written in the same order and store them in another array of integers named salary[] (contents of both files are shown below). Finally create a file stating for example. Mr. XYZ receive $75,500.00 per year (Note that salary is stored as integer but displayed here as double with a comma separating thousands. This formatting needs to be done using DecimalFormat Class)

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  • Selenium Webdriver Java - looking for alternatives for Actions and Robot when performing drag-and-drop

    - by Ja-ke Alconcel
    I first tried Actions class and the drag-and-drop does work on different elements, however it was unable to locate the a specific draggable element on it's exact screen/webpage position. Here's the code I've used: Point loc = driver.findElement(By.id("thiselement")).getLocation(); System.out.println(loc); WebElement drag = driver.findElement(By.id("thiselement")); Actions test = new Actions(driver); test.dragAndDropBy(drag, 0, 60).build().perform(); I checked the element with it's pixel location and it prints (837, -52), which was somewhere on top of the webpage and was pixels away from the actual element. Then I tried using the Robot class and works perfectly fine on my script, but can only provide constant successful runs on a single test machine, running it with a different machine with different screen resolution and screen size will render the script to fail due to the dependency of Robot on the pixel location of the element. The sample code of the Robot script I'm using: Robot dragAndDrop = new Robot(); dragAndDrop.mouseMove(945, 166); //actual pixel location of the draggable element dragAndDrop.mousePress(InputEvent.BUTTON1_MASK); sleep(3000); dragAndDrop.mouseMove(945, 226); dragAndDrop.mouseRelease(InputEvent.BUTTON1_MASK); sleep(3000); Is there any alternative for Actions and Robot to automate drag-and-drop? Or maybe a help on working the script to work on Actions as I really can't use Robot. Thanks in advance.

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  • Get annotations of return type in Java

    - by Apropos
    I'm using Spring MVC and am using aspects to advise my controllers. I'm running into one issue: controllers that return a value annotated with the @ResponseBody type. How are you able to find the annotations applied to the return type? @Around("myPointcut()") private Object checkAnnotations(ProceedingJoinPoint pjp) throws Throwable { Object result = pjp.proceed(); Method method = ((MethodSignature)pjp.getSignature()).getMethod(); System.out.println("Checking return type annotations."); for(Annotation annotation : method.getReturnType().getAnnotations()){ System.out.println(annotation.toString()); } System.out.println("Checking annotations on returned object."); for(Annotation annotation : result.getClass().getAnnotations()){ System.out.println(annotation.toString()); } return result; } Unfortunately, neither of these methods seem to have the desired effect. I can retrieve annotations on the type of object being returned, but not the ones being added at return time.

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  • Adding instances of a class to an Arraylist in java

    - by Olga
    I have 10 instances of the class movie which I wish to add to an Arraylist named Catalogue1 in a class containing a main method I write the following ArrayList catalogue1= new ArrayList () //the class movie is defined in another class Movie movie1= new Movie () Movie movie2= new Movie () Catalogue.Add (1, movie1) What is wrong? Should I define somewhere what kind of Objects this arraylist named catalogue should contain? Thank you in advance

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  • Why is run() not immediately called when start() called on a thread object in java

    - by pi
    Or is it? I have a thread object from: Thread myThread = new Thread(pObject); Where pObject is an object of a class implementing the Runnable interface and then I have the start method called on the thread object like so: myThread.start(); Now, my understanding is that when start() is called, the JVM implicitly (and immediately) calls the run() method which may be overridden (as it is in my case) However, in my case, it appears that the start() method is not called immediately (as desired) but until the other statements/methods are completed from the calling block i.e. if I had a method after the start() call like so: myThread.start(); doSomethingElse(); doSomthingElse() gets executed before the run() method is run at all. Perhaps I am wrong with the initial premise that run() is always called right after the start() is called. Please help! The desired again is making executing run() right after start(). Thanks.

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  • For-Each and Pointers in Java

    - by John
    Ok, so I'm tyring to iterate through an ArrayList and remove a specefic element. However, I am having some trouble using the For-Each like structure. When I run the following code: ArrayList<String> arr = new ArrayList<String>(); //... fill with some values (doesn't really matter) for(String t : arr) { t = " some other value "; //hoping this would change the actual array } for(String t : arr) { System.out.println(t); //however, I still get the same array here } My question in, how can I make 't' a pointer to 'arr' so that I am able to change the values in a for-each loop? I know I could loop through the ArrayList using a different structure, but this one looks so clean and readable, it would just be nice to be able to make 't' a pointer. All comments are appreciated! Even if you say I should just suck it up and use a different construct.

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  • How to extract byte-array from one xml and store it in another in Java

    - by grobartn
    So I am using DocumentBuilderFactory and DocumentBuilder to parse an xml. So it is DOM parser. But what I am trying to do is extract byte-array data (its an image encoded in base64) Store it in one object and later in code write it out to another xml encoded in base64. What is the best way to store this in btw. Store it as string? or as ByteArray? How can I extract byte array data in best way and write it out. I am not experienced with this so wanted to get opinion from the group. UPDATE: I am given XML I do not have control of incoming XML that comes in binary64 encoded < byte-array > ... base64 encoded image ... < /byte-array > Using parser I have I need to store this node and question is should that be byte or string and then writing it out to another node in new xml. again in base64 encoding. thanks

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