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  • Java: Using multiple Threads to paint simultaniously on a JPanel

    - by user347217
    I have a JPanel on which I wish to have several threads painting "animations" on. An "animation" consists of a JLabel with an ImageIcon on it, which is being moved from one area of the screen to another area. Now, problem is - I want several such animations to be portrayed on screen by those threads mentioned. Problem is - the JPanel's "paint()" method can only be trigged by one thread at a time - causing the animations to execute serially, instead of in a parallel way. Any idea how to have several such animations on screen at the same time?

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  • How to transform huge xml files in java?

    - by fx42
    As the title says it, I have a huge xml file (GBs) <root> <keep> <stuff> ... </stuff> <morestuff> ... </morestuff> </keep> <discard> <stuff> ... </stuff> <morestuff> ... </morestuff> </discard> </root> and I'd like to transform it into a much smaller one which retains only a few of the elements. My parser should do the following: 1. Parse through the file until a relevant element starts. 2. Copy the whole relevant element (with children) to the output file. go to 1. step 1 is easy with SAX and impossible for DOM-parsers. step 2 is annoying with SAX, but easy with the DOM-Parser or XSLT. so what? - is there a neat way to combine SAX and DOM-Parser to do the task?

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  • ArrayList to Array of Strings in java

    - by rajivpradeep
    ArrayList<String> newArray = new ArrayList<String>(); newArray = urlList.getUrl(); for( int i = 0 ; i < newArray.size();i++) { System.out.println(newArray.get(i)); } newArray.toArray(mStrings );// is this correct mStrings = newArray.toArray();// or this to convert ArrayList ot String array here for( int i = 0 ; i < mStrings.length;i++) { System.out.println(mStrings[i]); }

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  • Trying to get the associated value from an Enum at runtime in Java

    - by devoured elysium
    I want to accomplish something like the following (my interest is in the toInt() method). Is there any native way to accomplish this? If not, how can I get the integer associated with an enum value (like in C#) ? enum Rate { VeryBad(1), Bad(2), Average(3), Good(4), Excellent(5); private int rate; private Rate(int rate) { this.rate = rate; } public int toInt() { return rate; } } Thanks

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  • Code explanation in java

    - by Gandalf StormCrow
    Hello everyone, this morning I came across this code, and I have absolutely no idea what that means, can anyone explain me what do these represent, ex: public class MyClass<T> ... some bits of code then private Something<T> so; private OtherThing<T> to; private Class<T> c; Thank you

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  • Java:How to align Jpanels

    - by John
    I have this code but it doesn't work: jPanel1.add(jLabel1); jPanel2.add(jButton1); jPanel2.add(jButton2); jPanel3.add(jPanel1,jPanel1.TOP_ALIGNMENT); jPanel3.add(jPanel2,jPanel2.BOTTOM_ALIGNMENT); setContentPane(jPanel3); pack(); Please tell me why!

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  • Why does java.util.concurrent.ArrayBlockingQueue use 'while' loops instead of 'if' around calls to

    - by theFunkyEngineer
    I have been playing with my own version of this, using 'if', and all seems to be working fine. Of course this will break down horribly if signalAll() is used instead of signal(), but if only one thread at a time is notified, how can this go wrong? Their code here - check out the put() and take() methods; a simpler and more-to-the-point implementation can be seen at the top of the JavaDoc for Condition. Relevant portion of my implementation below. public Object get() { lock.lock(); try { if( items.size() < 1 ) hasItems.await(); Object poppedValue = items.getLast(); items.removeLast(); hasSpace.signal(); return poppedValue; } catch (InterruptedException e) { e.printStackTrace(); return null; } finally { lock.unlock(); } } public void put(Object item) { lock.lock(); try { if( items.size() >= capacity ) hasSpace.await(); items.addFirst(item); hasItems.signal(); return; } catch (InterruptedException e) { e.printStackTrace(); } finally { lock.unlock(); } } P.S. I know that generally, particularly in lib classes like this, one should let the exceptions percolate up.

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  • Java File.isDirectory() returns False for a Directory in Linux

    - by shelt536
    Please see code snippet: File[] additionalFiles = new File(FILE_PATH).listFiles(); boolean isDirectory = file.isDirectory(); I have verified that the directory path is correct, and when I run the code on Windows, the value of isDirectory is true (as it should be). Any suggestions as to why this occurs on Linux (RedHat Enterprise Linux)?

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  • initiliase the object in java

    - by harigm
    is it the right Way we initialise the the object? I have a Class Sample(); I want to intialise the Object in my Sample1 Class After intialisation I dont require to use the object of Sample Class. In that Case Can I initialise that object as new Sample(); instead of Sample s = new Sample(), if I am not going to use s anywhere in my Sample1 Class My question, is this a good practice to do that? will there be any after affects

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  • Java loop and increment problem

    - by user552961
    Can any one tell me what is the problem in my program? String a[],b[]; int c[] = new int[b.length]; for (int j = 0; j < a.length; j++) { for (int k = 0; k < b.length; k++) { if (b[k].equals(a[j])) { c[k]++; } else { c[k] = 0; } } } I have thousands of words stored in a HashMap. Now I want to check in every file that how many time one word occurred from allWords. Can you point out mistake in my program or give me your idea that how I can do it?

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  • Java getMethod with subclass parameter

    - by SelectricSimian
    I'm writing a library that uses reflection to find and call methods dynamically. Given just an object, a method name, and a parameter list, I need to call the given method as though the method call were explicitly written in the code. I've been using the following approach, which works in most cases: static void callMethod(Object receiver, String methodName, Object[] params) { Class<?>[] paramTypes = new Class<?>[params.length]; for (int i = 0; i < param.length; i++) { paramTypes[i] = params[i].getClass(); } receiver.getClass().getMethod(methodName, paramTypes).invoke(receiver, params); } However, when one of the parameters is a subclass of one of the supported types for the method, the reflection API throws a NoSuchMethodException. For example, if the receiver's class has testMethod(Foo) defined, the following fails: receiver.getClass().getMethod("testMethod", FooSubclass.class).invoke(receiver, new FooSubclass()); even though this works: receiver.testMethod(new FooSubclass()); How do I resolve this? If the method call is hard-coded there's no issue - the compiler just uses the overloading algorithm to pick the best applicable method to use. It doesn't work with reflection, though, which is what I need. Thanks in advance!

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  • What is the explanation of this java code ?

    - by M.H
    I have the following code : public class Main { public void method(Object o) { System.out.println("Object Version"); } public void method(String s) { System.out.println("String Version"); } public static void main(String args[]) { Main question = new Main(); question.method(null);//1 } } why is the result is "String Version" ? and why there is a compiler error if the first method takes a StringBuffer object ?

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  • Problem decrementing in Java with '-='

    - by hanesjw
    I'm making a scrolling game on Android and am having a hard time figuring out why the code below does not decrement past 0. Objects start at the end of the screen (so the x position is equal to the width of the screen) the objects move accross the screen by decrementing their x positions. I want them to scroll off of the screen, but when the x position hits 0, the objects just stay at 0, they do not move into the negatives. Here is my code to move objects on the screen private void incrementPositions(long delta) { float incrementor = (delta / 1000F) * Globals.MAP_SECTION_SPEED; for(Map.Entry<Integer, HashMap<Integer, MapSection>> column : scrollingMap.entrySet()) { for(Map.Entry<Integer, MapSection> row : column.getValue().entrySet()) { MapSection section = row.getValue(); section.x -= incrementor; } } } It works ok if I change section.x -= incrementor; to section.x = section.x - (int)incrementor; but if i do that the scrolling doesn't appear as smooth.

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  • Java nullPointerException with getter and setters on an object

    - by 12345
    I'm getting a nullPointerException below. Can someone explain why? Thanks! private SpatialPooler spatialPooler; private Region region; private Column column33; public void setUp() { this.spatialPooler = new SpatialPooler(); this.region = new Region(30, 40, 6, 8, 1.0f, 1, 1); this.column33 = this.region.getColumn(3, 3); } public void addActiveColumn(Column activeColumn) { this.activeColumns.add(activeColumn); // nullPointerException here! } public Column getActiveColumn(int x, int y) { for (Column activeColumn : this.activeColumns) { if (activeColumn.getX() == x && activeColumn.getY() == y) { return activeColumn; } } return null; } // in a test class that is in the same package. public void testGetAndAddActiveColumn() { this.spatialPooler.addActiveColumn(this.column33); assertNull(this.spatialPooler.getActiveColumn(3, 3)); this.column33.setActiveState(true); assertEquals(this.column33, this.spatialPooler.getActiveColumn(3, 3)); }

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  • Java inheritance 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 = method-call();` // 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 some-method(LIst<A> a) However, when I do: C c = new C(). c. some-method(b) I get an error that some-method is not applicable for the argument List, instead it's expecting to get List. Is there a good way to fix this problem? Many thanks!

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  • Java threading problem

    - by Krt_Malta
    Hi! I'm using multiple threads in my application. Basically I have a combo box and upon selecting Inbox, p1 resumes and p2 is suspended and upon selecting Send, p2 starts and p1 stops. Below is the code (I'm sure it's not perfect) public void modifyText(ModifyEvent e) { if (combo.getText().equals("Inbox")) { synchronized(p2) { p2.cont = false; } table.removeAll(); synchronized(p1) { p1.cont = true; p1.notify(); } } else if (combo.getText().equals("Sent")) { synchronized(p2) { p1.cont = false; } table.removeAll(); synchronized(p1) { p2.cont = true; p2.notify(); } } } }); and for P1 and P2 I have this inside their while loops: synchronized (this) { while (cont == false) try { wait(); } catch (Exception e) { } } ... As it is it's now working (I'm a beginner to threads). On pressing Sent in the combo box, I get an IllegalStateMonitorException. Could anyone help me solve the problem plz? Thanks and regards, Krt_Malta

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  • Can i query a List? Java

    - by Nitesh Panchal
    Hello, Say i have List<SomeObject> objList = new ArrayList<SomeObject>(); If someObject contains a field named id. Can we find it through some query like objList.filter('id=2'); wihout looping through the list? If not, then why? This can be so useful method and used as an alternative to write tedious for loop? Just a question that came to my mind so i thought i must clear it here :) Thanks in advance :)

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  • How to return a string from char[] array using recursion loop.(java)

    - by Daniel
    I am very bed in recursion... I need to convert a char[] array by using recursion loop only, into string. Without using for(),while()... loops. For example if i have char array: a[0]='H', a[1]='e', a[2]='l',a[3]= 'l',a[4]= 'o', it returns H e l l o. What I doing wrong? public String toFormattedString(char[] a) { int temp =a.length; if (a == null) return "null"; if (a.length == 0) return "0"; if( a.length == 1 ) else if( a[0] == a[a.length] ) return toFormattedString (a[a.length -1])+a[a.length];

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  • Dynamic Image Caching with Java

    - by zteater
    I have a servlet with an API that delivers images from GET requests. The servlet creates a data file of CAD commands based on the parameters of the GET request. This data file is then delivered to an image parser, which creates an image on the file system. The servlet reads the image and returns the bytes on the response. All of the IO and the calling of the image parser program can be very taxing and images of around 80kb are rendering in 3-4000ms on a local system. There are roughly 20 parameters that make up the GET request. Each correlates to a different portion of the image. So, the combinations of possible images is extremely large. To alleviate the loading time, I plan to store BLOBs of rendered images in a database. If a GET request matches one previously executed, I will pull from cache. Else, I will render a new one. This does not fix "first-time" run, but will help "n+1 runs". Any other ideas on how I can improve performance?

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