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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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  • 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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  • 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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  • 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 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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  • 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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  • 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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  • 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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  • 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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  • Cannot create an array of LinkedLists in Java...?

    - by kchau
    I'm working on a sparse matrix class that needs to use an array of LinkedLists to store the values of a matrix. Each element of the array (i.e. each LinkedList) represents a row of the matrix. And, each element in the LinkedLists represents a column and the stored value. In my class, I have a declaration of the array as: private LinkedList<IntegerNode>[] myMatrix; And, in my constructor for the SparseMatrix, I try to define: myMatrix = new LinkedList<IntegerNode>[numRows]; The error I end up getting is "Cannot create a generic array of LinkedList<IntegerNode>." So, I have two issues with this, 1) What am I doing wrong, and 2) Why is the type acceptable in the declaration for the array if it can't be created? Edit: IntegerNode is a class that I have created. And, all of my class files are packaged together.

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  • Java-Counting occurrence of word from huge textfile

    - by Naveen
    I have a text file of size 115MB. It consists of about 20 million words. I have to use the file as a word collection, and use it to search the occurrence of each user-given words from the collection. I am using this process as a small part in my project. I need a method for finding out the number of occurrence of given words in a faster and correct manner since i may use it in iterations. I am in need of suggestion about any API that i can make use or some other way that performs the task in a quicker manner. Any recommendations are appreciated.

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  • Why does (360 / 24) / 60 = 0 ... in Java

    - by Ankur
    I am trying to compute (360 / 24) / 60 I keep getting the answer 0.0 when I should get 0.25 In words: I want to divide 360 by 24 and then divide the result by 60 public class Divide { public static void main(String[] args){ float div = ((360 / 24) / 60); System.out.println(div); } } This prints out: 0.0 Why is that? Am I doing something really stupid, or is there a good reason for this

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  • Java variables across methods

    - by NardCake
    I'm making a basic text editor, and I have 2 methods the first one is triggered when a user click 'Open' and it prompts the user to pick a file and it opens the file fine. I just want to access the same file path which is in a variable in the method that is triggered when the user clicks save. My methods are public, Iv'e tried accessing it through a class, still no. Please help! Code: public void open(){ try{ //Open file JFileChooser fc = new JFileChooser(); fc.showOpenDialog(null); File file = fc.getSelectedFile(); String haha = file.getPath(); BufferedReader br = new BufferedReader(new FileReader(file.getPath())); String line; while((line = br.readLine()) != null){ text.append(line + "\n"); } } catch (FileNotFoundException e){ e.printStackTrace(); }catch (IOException e){ } } public void save(){ try { BufferedWriter bw = new BufferedWriter(new FileWriter(file.filePath)); bw.write(text.getText()); bw.close(); } catch (IOException e) { e.printStackTrace(); } }

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  • Insertion into BST without header Node JAVA

    - by Petiatil
    I am working on a recursive insertion method for a BST. This function is suppose to be a recursive helper method and is in a private class called Node. The Node class is in a class called BinarySearchTree which contains an instance variable for the root. When I am trying to insert an element, I get a NullPointerException at : this.left = insert(((Node)left).element); I am unsure about why this occurs. If I understand correctly, in a BST, I am suppose to insert the item at the last spot on the path transversed. Any help is appreciated! private class Node implements BinaryNode<E> { E item; BinaryNode<E> left, right; public BinaryNode<E> insert(E item) { int compare = item.compareTo(((Node)root).item); if(root == null) { root = new Node(); ((Node)root).item = item; } else if(compare < 0) { this.left = insert(((Node)left).item); } else if(compare > 0) { this.right = insert(((Node)right).item); } return root; } }

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  • Accessing variables in other classes (Java)

    - by George
    Why doesn't the following program return 0, since I am accessing p from a new A(), which has not had main called on it? public class A { public int p = 0; public static void main(String[] args) { p = Integer.parseInt(args[0]); new B().go(); } } class B { public void go() { System.out.println(new A().p); } }

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  • Converting Java code block to Objective-C

    - by user1123688
    I am trying to convert my Android app to iOS. This will be my first iOS app. I can't seem to translate this code properly. If someone wouldn't mind showing me how its done, that would be greatly appreciated. //scrambBase20 is a Byte array String descramble(String input){ char[] ret; ret = input.toCharArray(); int offset = -scrambBase20.length; for(int i=0;i<input.length();i++){ if(i%scrambBase20.length==0) offset+=scrambBase20.length; ret[scrambBase20[i%scrambBase20.length]+offset]=(char) ((byte) (input.charAt(i))^0x45); } String realRet = ""; for (char x : ret){ realRet+=x; } realRet = realRet.trim(); return realRet; }

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  • List Question in Java

    - by TiNS
    Hello All, I have a following ArrayList, [Title,Data1,Data2,Data3] [A,2,3,4] [B,3,5,7] And I would like to convert this one like this, [Title,A,B] [Data1,2,3] [Data2,3,5] [Data3,4,7] I'm bit confused with the approach. Any hint would be much appreciated. Thanks.

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