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  • Java App Engine - ranked counter

    - by Richard
    I understand the sharded counter, here: http://code.google.com/appengine/articles/sharding_counters.html The problem is that a simple counter will not work in my application. I am sorting my entities by a particular variable so I am returned not so much a count, but more of a rank. My current method is: SELECT COUNT(this) FROM Entity.class WHERE value <= ? Result + 1 is then the rank of the parameter in relation to the value variable in the persistent Entity objects. The limitation of this is the highest rank being returned is 1001 because count() can give a maximum of 1000. The reason I cannot store the rank on the Entity object is that the ranks are updated very often, and re-setting this rank variable would be much too costly. Any ideas on the best way to accomplish this?

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  • Java generic return type

    - by Colby77
    Hi, I'd like to write a method that can accept a type param (or whatever the method can figure out the type from) and return a value of this type so I don't have to cast the return type. Here is a method: public Object doIt(Object param){ if(param instanceof String){ return "string"; }else if(param instanceof Integer){ return 1; }else{ return null; } } When I call this method, and pass in it a String, even if I know the return type will be a String I have to cast the return Object. This is similar to the int param. How shall I write this method to accept a type param, and return this type?

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  • Java Nimbus LAF with transparent text fields

    - by Software Monkey
    I have an application that uses disabled JTextFields in several places which are intended to be transparent - allowing the background to show through instead of the text field's normal background. When running the new Nimbus LAF these fields are opaque (despite setting setOpaque(false)), and my UI is broken. It's as if the LAF is ignoring the opaque property. Setting a background color explicitly is both difficult in several places, and less than optimal due to background images actually doesn't work - it still paints it's LAF default background over the top, leaving a border-like appearance (the splash screen below has the background explicitly set to match the image). Any ideas on how I can get Nimbus to not paint the background for a JTextField? Note: I need a JTextField, rather than a JLabel, because I need the thread-safe setText(), and wrapping capability. Note: My fallback position is to continue using the system LAF, but Nimbus does look substantially better. See example images below. Conclusions The surprise at this behavior is due to a misinterpretation of what setOpaque() is meant to do - from the Nimbus bug report: This is a problem the the orginal design of Swing and how it has been confusing for years. The issue is setOpaque(false) has had a side effect in exiting LAFs which is that of hiding the background which is not really what it is ment for. It is ment to say that the component my have transparent parts and swing should paint the parent component behind it. It's unfortunate that the Nimbus components also appear not to honor setBackground(null) which would otherwise be the recommended way to stop the background painting. Setting a fully transparent background seems unintuitive to me. In my opinion, setOpaque()/isOpaque() is a faulty public API choice which should have been only: public boolean isFullyOpaque(); I say this, because isOpaque()==true is a contract with Swing that the component subclass will take responsibility for painting it's entire background - which means the parent can skip painting that region if it wants (which is an important performance enhancement). Something external cannot directly change this contract (legitimately), whose fulfillment may be coded into the component. So the opacity of the component should not have been settable using setOpaque(). Instead something like setBackground(null) should cause many components to "no long have a background" and therefore become not fully opaque. By way of example, in an ideal world most components should have an isOpaque() that looks like this: public boolean isOpaque() { return (background!=null); }

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  • Java - Regex problem

    - by Yatendra Goel
    I want a regex to find the following types of strings: http://anything.abc.tld http://anything.abc.tld/ where abc - abc always remains abc anything - it could be any string tld - it could be any tld (top-level-domain) like .com .net .co.in .co.uk etc.

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  • Java repaint is slow under certain conditions.

    - by Gabriel A. Zorrilla
    I'm doing a simple grid which each square is highlighted by the cursor: They are a couple of JPanels, mapgrid and overlay inside a JLayeredPane, with mapgrid on the bottom. Mapgrid just draws on initialization the grid, its paint metodh is: public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2d = (Graphics2D) g; g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); for (int i = 0; i < h; i++) { for (int j = 0; j < w; j++) { g2d.setColor(new Color(128, 128, 128, 255)); g2d.drawRect(tileSize * j, i * tileSize, tileSize, tileSize); } } In the overlay JPanel is where the highlighting occurs, this is what is repainted when the mouse is moved: public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2d = (Graphics2D) g; g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); g2d.setColor(new Color(255, 255, 128, 255)); g2d.drawRect((pointerX/tileSize)*tileSize,(pointerY/ tileSize)*tileSize, tileSize, tileSize); } I noticed that even though the base layer (mapgrid) is NOT repainted when the mouse moves, just the transparent overlay layer, the performance is lacking. If i give the overlay JPanel a background, its way faster. If i remove the mapgrid Antialiasing, its a bit faster too. I don't know why giving a background to the overlay layer (and thus, hiding the mapgrid) or disabling antialiasing in the mapgrid leads to much better performance. Is there a better way to do this? Why does this happen?

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  • Java - Get a list of all Classes loaded in the JVM

    - by Walter White
    Hi all, I would like to get a list of all the classes loaded in the JVM at a particular point in time. The classes are in a particular package and are accessible via /WEB-INF/classes and not through a jar file in /WEB-INF/lib. How would I get a list of classes? Would I simply get the classpath, list all the files, then look for the names? Walter

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  • Add Hexidecimal Header Info to JPEG File Using Java

    - by jboyd
    I need to add header info to a JPEG file in order to get it to work properly when shared on some websites, I've tracked down the correct info through a lot of Hex digging, but now I'm kind of stuck trying to get it into the file. I know where in the file it needs to go, and I know how long it is, my problem is that RandomAccessFile just overwrites existing data in the file and FileOutputStream appends the data to the end. I don't want either, I want to INSERT data starting at the third byte. My example code: File fileToChange = new File("someimage.jpg"); byte[] i = new byte[2]; i[0] = (byte)Integer.decode("0xcc"); i[1] = (byte)Integer.decode("0xcc"); RandomAccessFile f = new RandomAccessFile(new File("videothing.jpg"), "rw"); long aPositionWhereIWantToGo = 2; f.seek(aPositionWhereIWantToGo); // this basically reads n bytes in the file f.write((byte[])i); f.close(); So this doesn't work because it overwrites, and does not insert, I can't find any way to just insert data into a file

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  • Java Junit testing problem

    - by agazerboy
    Hi All, I am using Junit 4. My whole program is working fine. I am trying to write a test case. But there is one error... here is very basic sample test public class di extends TestCase{ private static Records testRec; public void testAbc() { Assert.assertTrue( "There should be some thing.", di.testRec.getEmployee() > 0); } } and when i run this it give me error that fName can not be null if i use super and do like this public TestAgnes() { super("testAbc"); } it work all fine. It wasn't this before with JUnit 3.X am I doing wrong or they changed it :( Sorry if I am not clear Is there any way to executre test without super? or calling functions etc. ?

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  • Java, LinkedList of Strings. Insert in alphabetical order

    - by user69514
    I have a simple linked list. The node contains a string (value) and an int (count). In the linkedlist when I insert I need to insert the new Node in alphabetical order. If there is a node with the same value in the list, then I simply increment the count of the node. I think I got my method really screwed up. public void addToList(Node node){ //check if list is empty, if so insert at head if(count == 0 ){ head = node; head.setNext(null); count++; } else{ Node temp = head; for(int i=0; i<count; i++){ //if value is greater, insert after if(node.getItem().getValue().compareTo(temp.getItem().getValue()) > 0){ node.setNext(temp.getNext()); temp.setNext(node); } //if value is equal just increment the counter else if(node.getItem().getValue().compareTo(temp.getItem().getValue()) == 0){ temp.getItem().setCount(temp.getItem().getCount() + 1); } //else insert before else{ node.setNext(temp); } } } }

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  • Weird Java Math ,10 ^ 1 = 11?

    - by Simon
    For an exercise I was writing a loop that turns a string into an integer without using the built in functions by multiplying each individual value by its numerical position. 75 would be 7*(10 ^ 1) + 5*(10 ^ 0), for example. However, for some reason (10 ^ 1) keeps coming back as 11. Is there some mistake I have made or an explanation for this?

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  • using Java interfaces

    - by mike_hornbeck
    I need to create interface MultiLingual, that allows to display object's data in different languages (not data itself, but introduction like "Author", "Title" etc.). Printed data looks like this : 3 grudnia 1998 10th of June 1924 Autor: Tolkien Tytul: LoTR Wydawnictwo: Amazon 2010 Author: Mitch Albom Title: Tuesdays with Morrie Publishing House: Time Warner Books 2003 37 360,45 PLN 5,850.70 GBP 3rd of December 1998 10th of June 1924 Author: Tolkien Title: LoTR Publishing House: Amazon 2010 Author: Mitch Albom Title: Tuesdays with Morrie Publishing House: Time Warner Books 2003 37,360.45 GBP 5,850.70 GBP Test code looks like this : public class Main { public static void main(String[] args){ MultiLingual gatecrasher[]={ new Data(3,12,1998), new Data(10,6,1924,MultiLingual.ENG), new Book("LoTR", "Tolkien", "Amazon", 2010), new Book("Tuesdays with Morrie", "Mitch Albom", "Time Warner Books",2003, MultiLingual.ENG), new Money(1232895/33.0,MultiLingual.PL), new Money(134566/23.0,MultiLingual.ENG), }; for(int i=0;i < gatecrasher.length;i++) System.out.println(gatecrasher[i]+"\n"); for(int i=0;i < gatecrasher.length;i++) System.out.println(gatecrasher[i].get(MultiLingual.ENG)+"\n"); } } So i need to introduce constants ENG, PL in MultiLingual interface, as well as method get(int language) : public interface MultiLingual { int ENG = 0; int PL= 1; String get(int lang); } And then I have class Book. Problem starts with the constructors. One of them needs to take MultiLingual.ENG as argument, but how to achieve that ? Is this the proper way? : class Book implements MultiLingual { private String title; private String publisher; private String author; public Book(String t, String a, String p, int y, MultiLingual lang){ } Or should I treat this MultiLingual.ENG as int variable , that will just change automatically constants in interface? Second constructor for book doesn't take MultLingual as argument, but following implementation is somehow wrong : public Book(String t, String a, String p, int y){ Book someBook = new Book(t, a, p, y, MultiLingual m); } I could just send int m in place of MultiLingual m but then I will have no control if language is set to PL or ENG. And finally get() method for Boook but I think at least this should be working fine: public String get(int lang){ String data; if (lang == ENG){ data = "Author: "+this.author+"\n"+ "Title: "+this.title+"\n"+ "Publisher: "+this.publisher+"\n"; } else { data = "Autor: "+this.author+"\n"+ "Tytul: "+this.title+"\n"+ "Wydawca: "+this.publisher+"\n"; } return data; } @Override public String toString(){ return ""; } }

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  • Taking User Input in Java

    - by jdbeverly87
    I'm creating a program that checks if a word or phrase is a palindrome. I have the actual "palindrome tester" figured out. What I'm stuck with is where and what to place in my code to have the console read out "Enter palindrome..." and then text. I've tried with IO but it doesnt work out right. Also, how do I create a loop to keep going? This code only allows one at a time `public class Palindrome { public static void main(String args[]) { String s=""; int i; int n=s.length(); String str=""; for(i=n-1;i>=0;i--) str=str+s.charAt(i); if(str.equals(s)) System.out.println(s+ " is a palindrome"); else System.out.println(s+ " is not a palindrome"); } }

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  • Write Java Method Signature with Annotated paramaters with JDT

    - by Scott
    Hi, I am writing an eclipse plug-in which generates code. I am leveraging eclipse jdt to gen out classes, fields, and methods. One of the requirements I have is to generate methods with annotated paramaters... public returnType foo(@someAnnotation int id) { ..... ..... } Does anybody know how to write out the @someAnnotation using JDT? To write out normal parameters in JDT you could do something like the following Signature.createTypeSignature("int", false)

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  • Static initializer in Java

    - by Szere Dyeri
    My question is about one particular usage of static keyword. It is possible to use static keyword to cover a code block within a class which does not belong to any function. For example following code compiles: public class Test { private static final int a; static { a = 5; doSomething(a); } private static int doSomething(int x) { return (x+5); } } If you remove the static keyword it complains because the variable a is final. However it is possible to remove both final and static keywords and make it compile. It is confusing for me in both ways. How am I supposed to have a code section that does not belong to any method? How is it possible to invoke it? In general, what is the purpose of this usage? Or better, where can I find documentation about this?

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  • Create a mirrored linked list in Java

    - by glacier89
    Linked-List: Mirror Consider the following private class for a node of a singly-linked list of integers: private class Node{ public int value; public Node next; } A wrapper-class, called, ListImpl, contains a pointer, called start to the first node of a linked list of Node. Write an instance-method for ListImpl with the signature: public void mirror(); That makes a reversed copy of the linked-list pointed to by start and appends that copy to the end of the list. So, for example the list: start 1 2 3 after a call to mirror, becomes: start 1 2 3 3 2 1 Note: in your answer you do not need to dene the rest of the class for ListImpl just the mirror method.

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  • Java - AWT / Swing - handling the Event Descriptor Thread

    - by waitinforatrain
    Hi, I have a question about the 'Event Descriptor Thread'. I have a Main class that is also a JFrame. It initialises the rest of the components in the code, some of them do not involve Swing and some of them do. Is it enough to simply initialise the Main class using the EDT like this?... public static void main(String[] args) { javax.swing.SwingUtilities.invokeLater(new Runnable() { public void run() { new Main(); } }); } This way everything would run on the Event Dispatcher thread.

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  • Java: Last access of 2D HashMap

    - by JamieFlowers
    I have the following structure: HashMap< String, HashMap< String, String Now i want to know the last accessed element in the 2nd dimension. I know there is TreeMap which makes sense in the 1rst dimension but after that it doesn't make any sense. How can I keep track of a 2D HashMap ordering? With access i mean: value = hashmap.get("a").get("1") value = hashmap.get("b").get("2") value = hashmap.get("c").get("3") hashmap.removeLast(); hashmap.removeLast(); hashmap.removeLast();

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  • Specify connection timeout in java.nio

    - by miorel
    Using non-blocking I/O, the code for connecting to a remote address looks something like: SocketChannel channel = SelectorProvider.provider().openSocketChannel(); channel.configureBlocking(false); channel.connect(address); The connection process will then have to be finished by invoking finishConnect() on the channel when some selector says the corresponding key isConnectable(). Is there a way to specify the connection timeout when using this idiom?

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  • Quick Java question about variables

    - by Spencer
    I'm declaring a variable: private static final String filename = "filename.txt"; First, does the order of private static final matter? If not, is there a standard excepted sequence or convention? Second, the filename in my application is fixed. Is this the best was to store it's value? Thanks, Spencer

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  • Java Charset problem on linux

    - by scot
    Hi, problem: I have a string containing special characters which i convert to bytes and vice versa..the conversion works properly on windows but on linux the special character is not converted properly.the default charset on linux is UTF-8 as seen with Charset.defaultCharset.getdisplayName() however if i run on linux with option -Dfile.encoding=ISO-8859-1 it works properly.. how to make it work using the UTF-8 default charset and not setting the -D option in unix environment. edit: i use jdk1.6.13 edit:code snippet works with cs = "ISO-8859-1"; or cs="UTF-8"; on win but not in linux String x = "½"; System.out.println(x); byte[] ba = x.getBytes(Charset.forName(cs)); for (byte b : ba) { System.out.println(b); } String y = new String(ba, Charset.forName(cs)); System.out.println(y); ~regards daed

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  • loop through HashMap Java jsp

    - by blub
    Hello, the related Questions couldn't help me very much. How can i loop through a HashMap in jsp like this example: <% HashMap<String, String> countries = MainUtils.getCountries(l); %> <select name="ccountry" id="ccountry" > <% //HERE I NEED THE LOOP %> </select>*<br/>

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  • Java JFrame method pack() problem

    - by Oliver
    Hi, I have a frame with 4 JPanels and 1 JScrollPane, the 4 panels are in border layout north, east, south, west and the scrollpane in the center. I have been trying to get the pack method for a frame fuctioning but when run you just get the title bar of the window. Any Ideas? Thank you in advance. JFrame conFrame; JPanel panel1; JPanel panel2; JPanel panel3; JPanel panel4; JScrollPane listPane; JList list; Object namesAr[]; ... ... ... namesAr= namesA.toArray(); list = new JList(namesAr); list.setSelectionMode(ListSelectionModel.SINGLE_SELECTION); list.setLayoutOrientation(JList.HORIZONTAL_WRAP); list.setVisibleRowCount(-3); list.addListSelectionListener(this); listPane = new JScrollPane(list); panel1 = new JPanel(); panel2 = new JPanel(); panel3 = new JPanel(); panel4 = new JPanel(); conFrame.setLayout(new BorderLayout()); panel1.setPreferredSize(new Dimension(100, 100)); panel2.setPreferredSize(new Dimension(100, 100)); panel3.setPreferredSize(new Dimension(100, 100)); panel4.setPreferredSize(new Dimension(100, 100)); panel1.setBackground(Color.red); panel2.setBackground(Color.red); panel3.setBackground(Color.red); panel4.setBackground(Color.red); conFrame.pack(); conFrame.add(panel1, BorderLayout.NORTH); conFrame.add(panel2, BorderLayout.EAST); conFrame.add(panel3, BorderLayout.SOUTH); conFrame.add(panel4, BorderLayout.WEST); conFrame.add(listPane, BorderLayout.CENTER); conFrame.setVisible(true);

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  • Runtime binding of XML Schema to Java code

    - by Yaneeve
    Hi all, The situation is thus: I have an application which provides editing capabilities to XML an file. This file follows a certain Schema. The Schema belongs to a subset of Schemas which actually follow a line of evolution from one to another - so they are not so different from one another. The main difference between the schemas is an enumeration of string labels. I now have need to save "meta data" in XML format (This is a second type of XML file). This "meta data" contains a list of labels from the set enumerated in the schema. The application can accept a new schema at runtime and adjust itself. Therefore I have an XML file that must be validated by two schemas one static containing the basic structure of the "meta data" stored in the XML and one which contains the 'proper' label enumeration. The latter schema is determined at runtime. I have glanced over JAXB, XMLBeans and JiBX. I can't figure out what technology to choose that would allow for a runtime bind of code and schema in the way that would most benefit my use-case. Any suggestions? Thanks!

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