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  • Maintaining a pool of DAO Class instances vs doing new operator

    - by Fazal
    we have been trying to benchmark our application performance in multiple way for sometime now. I always believed that object creation in java using Class.newInstance() was not slow (at least after 1.4 version of java). But we anyways did a test to use newInstance method vs mainitain an object pool of 1000 objects. We did about 200K iterations of loading data from DB using JDBC and populating these objects. I was amazed (even shocked) to see that newInstance code compared to object pool code was almost 10 times slower. These objects represent tables with about 50 fields and all string type. Can someone share there thoughts on this issue as now I am more confused if object pooling of atleast some DAO instances is a better option. The pool size as I see right now should be large enough to meet size of average requests. There is a flip side as my memory footprint will go up but I am beginning to wonder if this kind of idea makes sense atleast for some of the DAO entities representing tables of about 50 or more columns Please share your ideas and let me know if this has been tried by someone or am I missing some point here

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  • JPanel Appears Behind JMenuBar

    - by Matt H
    import javax.swing.JFrame; import javax.swing.JMenu; import javax.swing.JMenuBar; import javax.swing.JMenuItem; @SuppressWarnings("serial") public class Main extends JFrame { final int FRAME_HEIGHT = 400; final int FRAME_WIDTH = 400; public static void main(String args[]) { new Main(); } public Main() { super("Game"); GameCanvas canvas = new GameCanvas(); JMenuBar menuBar = new JMenuBar(); JMenu fileMenu = new JMenu("File"); JMenuItem startMenuItem = new JMenuItem("Pause"); menuBar.add(fileMenu); fileMenu.add(startMenuItem); super.setVisible(true); super.setSize(FRAME_WIDTH, FRAME_WIDTH); super.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); super.setJMenuBar(menuBar); } } import java.awt.Canvas; import java.awt.Graphics; import javax.swing.JPanel; @SuppressWarnings("serial") public class GameCanvas extends JPanel { public void paint(Graphics g) { g.drawString("hI", 0, 0); } } This code causes the string to appear behind the JMenuBar. To see the string, you must draw it at (0,10). I'm sure this must be something simple, so do you guys have any ideas?

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  • Why I do not see a static variable in a loop?

    - by Roman
    I have a static method which sets a variable: static String[] playersNames; public static void setParameters(String[] players) { playersNames = players; } Then I have a static block: static { JRadioButton option; ButtonGroup group = new ButtonGroup(); // Wright a short explanation of what the user should do. partnerSelectionPanel.add(new JLabel("Pleas select a partner:")); // Generate radio-buttons corresponding to the options available to the player. // Bellow is the problematic line causing the null pointer exception: for (String playerName: playersNames) { final String pn = playerName; option = new JRadioButton(playerName, false); option.addActionListener(new ActionListener(){ @Override public void actionPerformed(ActionEvent evt) { partner = pn; } }); partnerSelectionPanel.add(option); group.add(option); } partnerSelectionPanel.add(label); // Add the "Submit" button to the end of the "form". JButton submitButton = new JButton("Submit"); submitButton.addActionListener(new ActionListener(){ @Override public void actionPerformed(ActionEvent evt) { partnerSelected(); } }); partnerSelectionPanel.add(submitButton); } Compiler does not complain about anything but when I try to execute the code I get problems. In this place SelectPartnerGUI.setParameters(players); I have: Exception in thread "main" java.lang.ExceptionInitializerError. and it is cause by java.lang.NullpointerException at this place for (String playerName: playersNames). Does my program do not see the palyersNames?

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  • Riddle: Spot the serious bug in this bubble sort implementation

    - by ripper234
    (No, this isn't a homework assignment, I just found the bug and thought it might be useful to share it here) import java.util.List; public class BubbleSorter { public <T extends Comparable<T>> void sort(List<T> list) { while (true) { boolean didWork = false; for (int i = 0; i < list.size() - 1; ++i) { if (list.get(i).compareTo(list.get(i + 1)) > 0) { swap(list, i, i + 1); didWork = true; break; } } if (!didWork) return; } } private static <T> void swap(List<T> list, int i, int j) { T tmp = list.get(i); list.set(i, list.get(j)); list.set(j, tmp); } }

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  • Understanding the workings of equals and hashCode in a HashMap

    - by andandandand
    I have this test code: import java.util.*; class MapEQ { public static void main(String[] args) { Map<ToDos, String> m = new HashMap<ToDos, String>(); ToDos t1 = new ToDos("Monday"); ToDos t2 = new ToDos("Monday"); ToDos t3 = new ToDos("Tuesday"); m.put(t1, "doLaundry"); m.put(t2, "payBills"); m.put(t3, "cleanAttic"); System.out.println(m.size()); } } class ToDos{ String day; ToDos(String d) { day = d; } public boolean equals(Object o) { return ((ToDos)o).day == this.day; } // public int hashCode() { return 9; } } When // public int hashCode() { return 9; } is uncommented m.size() returns 2, when it's left commented it returns three. Why?

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  • How do I write JPA QL statements that hints to the runtime to use the DEFAULT value ?

    - by Jacques René Mesrine
    I have a table like so: mysql> show create table foo; CREATE TABLE foo ( network bigint NOT NULL, activeDate datetime NULL default '0000-00-00 00:00:00', ... ) In the domain object, FooVO the activeDate member is annotated as Temporal. If I don't set activeDate to a valid Date instance, a new record is inserted with NULLs. I want the default value to take effect if I don't set the activeDate member. Thanks.

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  • What is the difference between connection and read timeout for sockets?

    - by corgrath
    3 questions: 1) What is the difference between connection and read timeout for sockets? 2) What does connection timeout set to "infinity" mean? In what situation can it remain in an infinitive loop? and what can trigger that the infinity-loop dies? 3) What does read timeout set to "infinity" mean? In what situation can it remain in an infinitive loop? and what can trigger that the infinity-loop dies?

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  • Minimizing the number of boxes that cover a given set of intervals

    - by fortran
    Hi, this is a question for the algorithms gurus out there :-) Let S be a set of intervals of the natural numbers that might overlap and b a box size. Assume that for each interval, the range is strictly less than b. I want to find the minimum set of intervals of size b (let's call it M) so all the intervals in S are contained in the intervals of M. Trivial example: S = {[1..4], [2..7], [3..5], [8..15], [9..13]} b = 10 M = {[1..10], [8..18]} // so ([1..4], [2..7], [3..5]) are inside [1..10] and ([8..15], [9..13]) are inside [8..18] I think a greedy algorithm might not work always, so if anybody knows of a solution of this problem (or a similar one that can be converted into), that would be great. Thanks!

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  • Using set with values from a table

    - by gozzilli
    I'm writing a database of all DVDs I have at home. One of the fields, actors, I would like it to be a set of values from an other table, which is storing actors. So for every film I want to store a list of actors, all of which selected from a list of actors, taken from a different table. Is it possible? How do I do this? It would be a set of foreign keys basically. I'm using a MySQL database for a Django application (python), so any hint in SQL or Python would be much appreciated. I hope the question is clear, many thanks.

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  • servlet resopnse data for autocomplete

    - by shams haque
    Hello experts, Following code is in php. i want to do same in java. Please tell me how do i generate this type of array or collection in java. I need this to response to json autocomplete. <?php $q = strtolower($_GET["q"]); if (!$q) return; $items = array( "Peter Pan"=>"[email protected]", "Molly"=>"[email protected]", "Forneria Marconi"=>"[email protected]", "Master Sync"=>"[email protected]", "Dr. Tech de Log"=>"[email protected]", "Don Corleone"=>"[email protected]", "Mc Chick"=>"[email protected]", "Donnie Darko"=>"[email protected]", "Quake The Net"=>"[email protected]", "Dr. Write"=>"[email protected]" ); $result = array(); foreach ($items as $key=>$value) { if (strpos(strtolower($key), $q) !== false) { array_push($result, array( "name" => $key, "to" => $value )); } } echo json_encode($result); ?>

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  • Backreferences syntax in replacement strings (why dollar sign?)

    - by polygenelubricants
    In Java, and it seems in a few other languages, backreferences in the pattern is preceded by a slash (e.g. \1, \2, \3, etc), but in a replacement string it's preceded by a dollar sign (e.g. $1, $2, $3, and also $0). Here's a snippet to illustrate: System.out.println( "left-right".replaceAll("(.*)-(.*)", "\\2-\\1") // WRONG!!! ); // prints "2-1" System.out.println( "left-right".replaceAll("(.*)-(.*)", "$2-$1") // CORRECT! ); // prints "right-left" System.out.println( "You want million dollar?!?".replaceAll("(\\w*) dollar", "US\\$ $1") ); // prints "You want US$ million?!?" System.out.println( "You want million dollar?!?".replaceAll("(\\w*) dollar", "US$ \\1") ); // throws IllegalArgumentException: Illegal group reference Questions: Is the use of $ for backreferences in replacement strings unique to Java? If not, what language started it? What flavors use it and what don't? Why is this a good idea? Why not stick to the same pattern syntax? Wouldn't that lead to a more cohesive and an easier to learn language? Wouldn't the syntax be more streamlined if statements 1 and 4 in the above were the "correct" ones instead of 2 and 3?

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  • How to import a class from default package

    - by mykhaylo
    Hi, I am using Eclipse 3.5 and I have created a project with some package structure along with the default package. I have one class in default package - Calculations.java and I want to make the use of that class in any of the package (for instance in com.company.calc). When I try to make the use of the class which is default package, its giving me compile error. Its not able to recognise the class in default package. Where is a problem? Calculations.java - source code public class Calculations{ native public int Calculate(int contextId); native public double GetProgress(int contextId); static { System.loadLibrary("Calc"); } } I can put my class in any other package. This class has some native method which is implemented in Delphi . If I put that class in any of the folder,I will have to make the change that DLL which I want to avoid(really - I can not). Thats why I put my class in the default package.

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  • Why can't I wrap the ServletRequest when trying to capture JSP Output

    - by Patrick Cornelissen
    I am trying to dispatch in a servlet request handler to the JSP processor and capture the content of it. I am providing wrapper instances for the ServletRequest and ServletResponse, they implement the corresponding HTTPServletRequest/-Response interfaces, so they should be drop-in replacements. All methods are currently passed to the original Servlet Request object (I am planning to modify some of them soon). Additionally I have introduced some new methods. (If you want to see the code: http://code.google.com/p/gloudy/source/browse/trunk/gloudyPortal/src/java/org/gloudy/gloudlet/impl/RenderResponseImpl.java) The HttpServletResponse uses it's own output streams to capture the output. When I try to call request.getRequestDispatcher("/WEB-INF/views/test.jsp").include(request, response); With my request and response wrappers the method returns and no content has been captured. When I tried to pass the original request object it worked! But that's not what I need in the long run... request.getRequestDispatcher("/WEB-INF/views/test.jsp").include(request.getServletRequest(), response); This works. getservletRequest() returns the original Request, given by the servlet container. Does anyone know why this is not working with my wrappers?

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  • Interpreting WPF Dependency properties as a set.

    - by moogs
    So, I have a control. It displays an image based some xml document and an optional parameter "Document" - XML document "RenderingOption" - optional image-rendering ( sharpen, soften ) So: <XMLRenderingWidget Document="xxxxxx"/> The above will render the document once <XMLRenderingWidget Document="xxxxxx" RenderingOption="Sharpen"/> The above will, sometimes render the document once, more oftentimes: Perform the rendering of the document as if no Rendering was set then, re-render the document with the Sharpen option I do the rendering on the PropertyChangedCallback assigned to the property. How do I tell the control to "hey, before doing the rendering, apply the changes on the other properties being set, too" Is this not possible? Should I bundle them up as one property instead?

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  • How do implement a breadth first traversal?

    - by not looking for answer
    //This is what I have. I thought pre-order was the same and mixed it up with depth first! import java.util.LinkedList; import java.util.Queue; public class Exercise25_1 { public static void main(String[] args) { BinaryTree tree = new BinaryTree(new Integer[] {10, 5, 15, 12, 4, 8 }); System.out.print("\nInorder: "); tree.inorder(); System.out.print("\nPreorder: "); tree.preorder(); System.out.print("\nPostorder: "); tree.postorder(); //call the breadth method to test it System.out.print("\nBreadthFirst:"); tree.breadth(); } } class BinaryTree { private TreeNode root; /** Create a default binary tree */ public BinaryTree() { } /** Create a binary tree from an array of objects */ public BinaryTree(Object[] objects) { for (int i = 0; i < objects.length; i++) { insert(objects[i]); } } /** Search element o in this binary tree */ public boolean search(Object o) { return search(o, root); } public boolean search(Object o, TreeNode root) { if (root == null) { return false; } if (root.element.equals(o)) { return true; } else { return search(o, root.left) || search(o, root.right); } } /** Return the number of nodes in this binary tree */ public int size() { return size(root); } public int size(TreeNode root) { if (root == null) { return 0; } else { return 1 + size(root.left) + size(root.right); } } /** Return the depth of this binary tree. Depth is the * number of the nodes in the longest path of the tree */ public int depth() { return depth(root); } public int depth(TreeNode root) { if (root == null) { return 0; } else { return 1 + Math.max(depth(root.left), depth(root.right)); } } /** Insert element o into the binary tree * Return true if the element is inserted successfully */ public boolean insert(Object o) { if (root == null) { root = new TreeNode(o); // Create a new root } else { // Locate the parent node TreeNode parent = null; TreeNode current = root; while (current != null) { if (((Comparable)o).compareTo(current.element) < 0) { parent = current; current = current.left; } else if (((Comparable)o).compareTo(current.element) > 0) { parent = current; current = current.right; } else { return false; // Duplicate node not inserted } } // Create the new node and attach it to the parent node if (((Comparable)o).compareTo(parent.element) < 0) { parent.left = new TreeNode(o); } else { parent.right = new TreeNode(o); } } return true; // Element inserted } public void breadth() { breadth(root); } // Implement this method to produce a breadth first // search traversal public void breadth(TreeNode root){ if (root == null) return; System.out.print(root.element + " "); breadth(root.left); breadth(root.right); } /** Inorder traversal */ public void inorder() { inorder(root); } /** Inorder traversal from a subtree */ private void inorder(TreeNode root) { if (root == null) { return; } inorder(root.left); System.out.print(root.element + " "); inorder(root.right); } /** Postorder traversal */ public void postorder() { postorder(root); } /** Postorder traversal from a subtree */ private void postorder(TreeNode root) { if (root == null) { return; } postorder(root.left); postorder(root.right); System.out.print(root.element + " "); } /** Preorder traversal */ public void preorder() { preorder(root); } /** Preorder traversal from a subtree */ private void preorder(TreeNode root) { if (root == null) { return; } System.out.print(root.element + " "); preorder(root.left); preorder(root.right); } /** Inner class tree node */ private class TreeNode { Object element; TreeNode left; TreeNode right; public TreeNode(Object o) { element = o; } } }

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  • XSL: Get variable data without exslt:node-set

    - by Louis W
    Using native XSL lib in PHP. Is it possible to get a node value inside a variable without having to call it through exslt:node-set every time.... it long and ugly. <xsl:variable name="mydata"> <foo>1</foo> <bar>2</bar> </xsl:variable> <!-- How currently being done --> <xsl:value-of select="exslt:node-set($mydata)/foo" /> <!-- I want to be able to do this --> <xsl:value-of select="$mydata/foo" />

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  • Why setPreferredSize does not change the size of the button?

    - by Roman
    Here is the code: import javax.swing.*; import java.awt.event.*; import java.awt.*; public class TestGrid { public static void main(String[] args) { JFrame frame = new JFrame("Colored Trails"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); JPanel mainPanel = new JPanel(); mainPanel.setLayout(new BoxLayout(mainPanel, BoxLayout.Y_AXIS)); JPanel panel = new JPanel(); panel.setLayout(new GridLayout(4, 9)); panel.setMaximumSize(new Dimension(9*30-20,4*30)); JButton btn; for (int i=1; i<=4; i++) { for (int j=1; j<=4; j++) { btn = new JButton(); btn.setPreferredSize(new Dimension(30, 30)); panel.add(btn); } btn = new JButton(); btn.setPreferredSize(new Dimension(30, 10)); panel.add(btn); for (int j=1; j<=4; j++) { btn = new JButton(); btn.setPreferredSize(new Dimension(30, 30)); panel.add(btn); } } mainPanel.add(panel); frame.add(mainPanel); frame.setSize(450,950); frame.setVisible(true); } } I suppose to have a table of buttons with 4 rows and 9 columns. And the middle column should be narrower that other columns. I tried Dimension(30, 10) and Dimension(30, 10) both have no effect on the width of the middle column. Why?

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  • jvm issue at startup

    - by Mack
    I can set the max memory as 1000 and not more than that, if I set the memory more than that, it throws the following error. Error occurred during initialization of VM Could not reserve enough space for object heap Could not create the Java virtual machine. My question is, why jvm looks for the max memory at startup? Thanks in advance.

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  • Synchronizing screencasting (ffmpeg) and capturing from the webcam (OpenCV)

    - by lyuba
    As from my previous questions, I am trying to build a simple eye tracker. Decided to start from a Linux version (run Ubuntu). To complete this task one should organize screencasting and webcam capturing in such way that frames from both streams exactly match each other and there is the same number of frames in each of them totally. Screencasting fsp fully depends on the camera's fsp, so each time we get the image from the webcam we can potentially grab a screen frame and stay happy. However, all the tools for the fast screencasting, like ffmpeg, for example, return the .avi file as the result and require the fsp already known to be started. From the other side, tools like Java+Robot or ImageMagick seem to require around 20ms to return the .jpg screenshot, which is pretty slow for the task. But they may be requested right after each time the webcam frame is grabbed and provide the needed synchronization. So the sub-questions are: 1. Does the USD camera's frame rate vary during a single session? 2. Are there any tools which provide fast screencasting frame by frame? 3. Is there any way to make ffmpeg push a new frame to the .avi file only when program initiates this request? For my task I may either use C++ or Java. I am, actually, an interface designer, not the driver programmer, and this task seems to be pretty low-level. I would be grateful for any suggestion and tip!

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  • TreeMap sort by value

    - by vito huang
    I'm new to java, i want to write an comparator to that will let me sort TreeMap by value instead of the default natural sorting. i tried something like this, but can't find out what went wrong: import java.util.*; class treeMap { public static void main(String[] args) { System.out.println("the main"); byValue cmp = new byValue(); Map<String, Integer> map = new TreeMap<String, Integer>(cmp); map.put("de",10); map.put("ab", 20); map.put("a",5); for (Map.Entry<String,Integer> pair: map.entrySet()) { System.out.println(pair.getKey()+":"+pair.getValue()); } } } class byValue implements Comparator<Map.Entry<String,Integer>> { public int compare(Map.Entry<String,Integer> e1, Map.Entry<String,Integer> e2) { if (e1.getValue() < e2.getValue()){ return 1; } else if (e1.getValue() == e2.getValue()) { return 0; } else { return -1; } } } I guess what am i asking is what controls what get pass to comparator function, can i get an Map.Entry pass to comparator?

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  • Search and replace with sed

    - by Binoy Babu
    Last week I accidently externalized all my strings of my eclipse project. I need to revert this and my only hope is sed. I tried to create scripts but failed pathetically because I'm new with sed and this would be a very complicated operation. What I need to do is this: Strings in class.java file is currently in the following format(method) Messages.getString(<key>). Example : if (new File(DataSource.DEFAULT_VS_PATH).exists()) { for (int i = 1; i <= c; i++) { if (!new File(DataSource.DEFAULT_VS_PATH + Messages.getString("VSDataSource.89") + i).exists()) { //$NON-NLS-1$ getnewvfspath = DataSource.DEFAULT_VS_PATH + Messages.getString("VSDataSource.90") + i; //$NON-NLS-1$ break; } } } The key and matching Strings are in messages.properties file in the following format. VSDataSource.92=No of rows in db = VSDataSource.93=Verifying db entry : VSDataSource.94=DB is open VSDataSource.95=DB is closed VSDataSource.96=Invalid db entry for VSDataSource.97=\ removed. So I need the java file back in this format: if (new File(DataSource.DEFAULT_VS_PATH).exists()) { for (int i = 1; i <= c; i++) { if (!new File(DataSource.DEFAULT_VS_PATH + "String 2" + i).exists()) { //$NON-NLS-1$ getnewvfspath = DataSource.DEFAULT_VS_PATH + "String 1" + i; //$NON-NLS-1$ break; } } } How can I accomplish this with sed? Or is there an easier way?

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  • Raw types and subtyping

    - by Dmitrii
    We have generic class SomeClass<T>{ } We can write the line: SomeClass s= new SomeClass<String>(); It's ok, because raw type is supertype for generic type. But SomeClass<String> s= new SomeClass(); is correct to. Why is it correct? I thought that type erasure was before type checking, but it's wrong. From Hacker's Guide to Javac When the Java compiler is invoked with default compile policy it performs the following passes: parse: Reads a set of *.java source files and maps the resulting token sequence into AST-Nodes. enter: Enters symbols for the definitions into the symbol table. process annotations: If Requested, processes annotations found in the specified compilation units. attribute: Attributes the Syntax trees. This step includes name resolution, type checking and constant folding. flow: Performs data ow analysis on the trees from the previous step. This includes checks for assignments and reachability. desugar: Rewrites the AST and translates away some syntactic sugar. generate: Generates Source Files or Class Files. Generic is syntax sugar, hence type erasure invoked at 6 pass, after type checking, which invoked at 4 pass. I'm confused.

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  • How can I work around WinXP using ports 1025-5000 as ephemeral?

    - by Chris Dolan
    If you create a TCP client socket with port 0 instead of a non-zero port, then the operating system chooses any free ephemeral port for you. Most OSes choose ephemeral ports from the IANA dynamic port range of 49152-65535. However in Windows Server 2003 and earlier (including XP) Microsoft used ports 1025-5000 as the ephemeral range, according to their bind() documentation. I run multiple Java services on the same hardware. On rare occasions, this range collides with well-known ports that I use for other services (e.g. port 4160 for Jini discovery). While rare, this has caused real problems. Is there any easy way to tell Windows or Java to use a different port range for client sockets? Microsoft's docs indicate that I can change the high end of that range via the MaxUserPort TcpIP registry setting, but I see no way to change the low end. Update: I've made some progress on this. It looks like Microsoft has a concept of reserved ports that are exceptions to the ephemeral port range. There's a registry setting that lets you change this permanently and apparently there must be an API to do the same thing because there's a data structure that holds high/low values for reserved port ranges, but I can't find the actual function call anywhere... The registry solution may work, but now I'm fixated on this API.

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