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• How to draw a filled circle in Java?

  - by Roman

  I have a JPanel with a Grid Layout. In the "cells" of the grid I can put different elements (for example JButtons). There is no problems with that. But now I want to put a filled circle in some of the cells. I also would like to relate an ActionListener with these circles. In more details, if I click the circle it disappears from the current cell and appears in another one. How can I do it in Java? I am using Swing.

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• Updating a database periodically with Java

  - by MSR

  I would like to perform updates to a MySQL database using two separate classes (that do different things) -- one doing so every 10 seconds, and the second every minute. I have a few gaps in my Java knowledge and I'm wondering what the best way to achieve it is. Importantly, if connectivity to the database is lost, I need reconnection attempts to occur indefinitely, and I'm guessing the use of Prepared Statements will make queries more efficient. Should the connection to the database be left open all the time or closed between the updates being run? Maybe I also need to think about clearing objects/resources out of memory if the class instances are going to be run indefinitely.

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• Deploy Java application on MacOSX (from a Windows system)

  - by Matías

  Hello, Here's the deal. I'm just starting with Java programming, I've made a simple application that uses SWT graphic library and I want to deploy it on a Mac (running the latest version of MacOS X). I did all the programming in my Windows 7 machine, so here are my questions: Q1) Can I make an executable file for MacOS X from my Windows machine? How? (I saw that it's possible to create .exe files on Windows, instead of using .jar; I want to do the same for the Mac, of course it won't be an .exe) Q2) If I export my project in Eclipse and I choose Runnable JAR File and then on Library Handling I pick Extract required libraries into generated JAR or Package required libraries into generated JAR I end up with a huge .JAR (about 15MB of size, my application consist in just a button on a Window and a tiny method that doesn't do much). Is that considered normal? Here's the list of libraries that my project appears to be using: Thanks in advance.

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• On demand population of dropdown menu Java/Swing?

  - by Cookie Monster

  When I code a popup menu, I can check the mouse event and then before calling show() prepare the menu. Now I want a similar functionality for drop down menus, that live in the menu bar. For example I have the following menu bar layout: Menu 1 MenuItem 1.1 MenuItem 1.1.1 MenuItem 1.1.2 .. MenuItem 1.1.n Menu 2 Basically I want to generate the list MenuItem 1.1.1, MenuItem 1.1.2, ..., MenuItem 1.1.n dynamically when the drop down menu is invoked and before it is shown. How could I do this in Java/Swing? Best Regards

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• Java PreparedStatement Throws MySQLSyntaxErrorException

  - by sqlBugs

  I have the following Java code: String query = "Select 1 from myTable where name = ? and age = ?"; PreparedStatement stmt = conn.prepareStatement(query); stmt.setString(1, name); stmt.setInt(2, age); ResultSet rs = stmt.executeQuery(); Whenever I run the above code, it throws an exception on line 2 (where the PreparedStatement is declared): Error 0221202: SQLException = com.mysql.jdbc.exceptions.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '? AND age = ?' at line 1 Does anyone have any suggestions about what I am doing wrong? Thanks!

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• Java: Get current Date and Time from Server not System clock

  - by Insectatorious

  In my Java program, I need to create an instance of the current moment in time. I use Date date = new Date(); This gives me the current date and time as per the host machine's system clock. Is there any way I can get the current date and time from an online server? The world time server perhaps? I have seen this post and it describes what I want but I'm afraid I need more help than what's provided there. In a nutshell, I want to get a date and time that is not dependant on the host machine's system clock. Thanks!

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• Java: How to clear socket bindings

  - by Matt1776

  I am having a few issues with sockets within my Java SIP client. When I bind to an address and port, if something goes wrong I have to attempt to reconnect, usually after I've stopped and restarted the process. Problem with that is then the port is bound and I am forced to increment the local port. How can I remove the binding to the port I am targeting before binding to it? If that isnt possible, then how can I trap the process just before it ends so that I can locate the socket binding and close it manually?

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• retrieving 'nulls' from website using Java URL input stream

  - by Roio

  hi all, i'm trying to read the text from a website using the Java URL input stream as follows - URL u = new URL(str); br3 = new BufferedReader(new InputStreamReader(u.openStream())); while(true) System.out.println(br3.readLine()); this seems to work fine for most websites, but for some url shortening services like linkbee, the object draws a blank. e.g. http://linkbee.com/FUAKF, i can view the source code using an explorer, however i repeatedly get nulls when i use the above code.

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• Duel Masters game in Java

  - by Arun Ramasubramanian

  I was trying to make a Duel Masters card game in Java using BlueJ, and came up with a lot of ideas. However, I could not exactly figure out how to sort a deck on basis of the card names in the game. I have an array of Card objects(each has, as its instance variables: String name, int cost, int civ), and I want to sort them based on name. ie: if I have the cards "Pyrofighter Magnus", "Bazagazeal Dragon" and another "Pyrofighter Magnus" in the array, the cards should be sorted on basis of their names. I know that I could use compareTo(), but is there an easier method? Anyone? Remember, the method that sorts the cards should be a modifier.

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• illigal start of type error (java).

  - by David

  here is the relevent code snippet: public static Rand searchCount (int[] x) { int a ; int b ; int c ; int d ; int f ; int g ; int h ; int i ; int j ; Rand countA = new Rand () ; for (int l= 0; l<x.length; l++) { if (x[l] = 0) a++ ; else if (x[l] = 1) b++ ; } } return countA ; } (Rand is the name of the class that this method is in) when compiling it get this error message: Rand.java:77: illegal start of type return countA ; ^ what's going wrong here? what does this error message mean?

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• Java Authenticator on a per connection basis?

  - by Martijn Laarman

  I'm building an Eclipse plugin that talks to a REST interface which uses Basic Authentication. When the authentication fails I would like to popup my plugin's settings dialog and retry. Normally I could use the static Authenticator.setDefault() to setup an authenticator for all HttpURLConnection's for this, but since I am writing a plugin I don't want to overwrite Eclipse's default Authenticator (org.eclipse.ui.internal.net.auth); I thought of setting my custom Authenticator before loading and putting Eclipse's default back afterwards, but I imagine this will cause all sorts of race issues with multithreading so I quickly lost that notion. Google searches yield all sorts of results basically telling me it's not possible: The Java URLConnection API should have a setAuthenticator(Authenticator) method for making it easier to use this class in multi-threaded context where authentication is required. Source If applications contains few third party plugins and each plugin use its own Authenticator what we should do? Each invocation of "Authenticator.setDefault()" method rewrite previously defined Authenticator... Source Are there any different approaches that might help me overcome this issue?

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• how to compress a PNG image using Java

  - by 116213060698242344024

  Hi I would like to know if there is any way in Java to reduce the size of an image (use any kind of compression) that was loaded as a BufferedImage and is going to be saved as an PNG. Maybe some sort of png imagewriteparam? I didnt find anything helpful so im stuck. heres a sample how the image is loaded and saved public static BufferedImage load(String imageUrl) { Image image = new ImageIcon(imageUrl).getImage(); bufferedImage = new BufferedImage(image.getWidth(null), image.getHeight(null), BufferedImage.TYPE_INT_ARGB); Graphics2D g2D = bufferedImage.createGraphics(); g2D.drawImage(image, 0, 0, null); return bufferedImage; } public static void storeImageAsPng(BufferedImage image, String imageUrl) throws IOException { ImageIO.write(image, "png", new File(imageUrl)); }

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• Java: set-size List issue UnsupportedOperationException thrown

  - by tuckster

  I am having a problem changing a List that has a set-size in Java. I understand that I can't add or remove from this list but why can't I use set? When I use set the UnsupportedOperationException is thrown as well as when I use add and remove which is expected. set public Object set(int index, Object element) Replaces the element at the specified position in this list with the specified element (optional operation). I understand its an optional operation its just that want to replace that one element of the list with another element. Is there any way I can do this?

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• how to use ByteArrayOutputStream and DataOutputStream simultaneously (Java)

  - by Manuel

  Hi! I'm having quite a problem here, and I think it is because I don't understand very much how I should use the API provided by Java. I need to write an int and a byte[] into a byte[] I thought of using a DataOutputStream to solve the data writing with writeInt(int i) and write(byte[] b), and to be able to put that into a byte array, I should use ByteArrayOutputStream's method toByteArray(). I understand that this classes use the Wrapper pattern, so I had two options: DataOutputStream w = new DataOutputStream(new ByteArrayOutputStream()); or ByteArrayOutputStream w = new ByteArrayOutputStream(new DataOutputStream()); but in both cases, I "loose" a method. in the first case, I can't access the toByteArray method, and in the second, I can't access the writeInt method. How should I use this classes together?

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• how to return value from groovy to java

  - by Sid

  Hi I am very new to groovy and having trouble with some parts. I have a jsp page tied to a servlet that runs groovy scripts. I am able to get to the groovy script from the servlet. But after the script runs how do I return the response from the groovy script back to the servlet to be displayed in the jsp page? My java servlet code is as follows: File file = new File("TestScript.groovy"); ClassLoader parent = getClass().getClassLoader(); GroovyClassLoader loader = new GroovyClassLoader(parent); Class groovyClass = loader.parseClass(file); Object[] args = {}; GroovyObject groovyObject = (GroovyObject) groovyClass.newInstance(); groovyObject.invokeMethod("runTest", args);

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• Java Package, Project , NoSuchMethod error

  - by hamam

  I have 2 projects linked and these 2 projects each have a package under them. XProject - XPackage - XClass - X1Method(); X2Method(); YProject - YPackage - YClass - Y1Method(); I'm trying to call X1 and X2 methods from Y1 Method. I can call X1 Method but when I call X2 method I get a runtime error (java.lang.NoSuchMethodError:) All methods are public and there is nothing wrong with method names. It is just nonsense to have one of them working while other is giving runtime errors. Any help would be appreciated. Thanks.

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• Java concurrency - Should block or yield?

  - by teto

  Hi, I have multiple threads each one with its own private concurrent queue and all they do is run an infinite loop retrieving messages from it. It could happen that one of the queues doesn't receive messages for a period of time (maybe a couple seconds), and also they could come in big bursts and fast processing is necessary. I would like to know what would be the most appropriate to do in the first case: use a blocking queue and block the thread until I have more input or do a Thread.yield()? I want to have as much CPU resources available as possible at a given time, as the number of concurrent threads may increase with time, but also I don't want the message processing to fall behind, as there is no guarantee of when the thread will be reescheduled for execution when doing a yield(). I know that hardware, operating system and other factors play an important role here, but setting that aside and looking at it from a Java (JVM?) point of view, what would be the most optimal?

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• A strange error in java generic.

  - by ???

  This is ok: Class<? extends String> stringClass = "a".getClass(); But this gets error: <T> void f(T obj) { Class<? extends T> objClass = obj.getClass(); } I know I can cast it like: <T> void f(T obj) { @SuppressWarnings("unchecked") Class<? extends T> objClass = (Class<? extends T>) obj.getClass(); } But why the previous error? Will the next release of Java 7 will support such usage?

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• Java: Can't implement runnable on a test case: void run() collides

  - by Zombies

  So I have a test case that I want to make into a thread. I cannot extend Thread nor can I implement runnable since TestCase already has a method void run(). The compilation error I am getting is Error(62,17): method run() in class com.util.SeleneseTestCase cannot override method run() in class junit.framework.TestCase with different return type, was class junit.framework.TestResult. What I am trying to do is to scale a Selenium testcase up to perform stress testing. I am not able to use selenium grid/pushtotest.com/amazon cloud at this time (installation issues/install time/resource issues). So this really is more of a Java language issue for me.

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• Program output to file in Java (and reading it again)

  - by Cohagen

  I have a large main method in an IO class which creates objects from four different classes in my program (which all use one another to some extent). My main method takes all info in using a scanner, from the console window, and uses this info to call the constructors and methods in the other classes. As this is my first full program in Java I have been focussed on making the main method work via the console, without properly considering file input and output. I cannot see an easy way of making that work now. Ideally what I require is some way of writing everything I input to the console while running the main method to a file, in a format that can be read again and inputed back through the main method? I have refrained from posting the main method as it is 250+ lines long, but will post any relevant parts of it if required. Any help appreciated

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• RFC822 Timezone Parsing in Java

  - by Jamen

  Hi, I have a JS date that is being converted by Dojo into RFC822 format. The function call - dojo.date.toRfc3339(jsDate), generates the following date - 2007-02-26T20:15:00+02:00. I have an application that uses a Java date SimpleDateFormat to parse in the dates generated above. I am having problems parsing this date format due to the timezone. I have attempted to use yyyy-mm-DD'T'hh:mm:ssZ This fails as the 'Z' for timezone doesn't expect a ':' character. Does anyone know how I would specify a pattern to handle a RFC822 date with the ':'? Thanks Jamen

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• What Java tools/apis to use for decrypting/encrypting

  - by Java_bear

  I am trying to decrypt (and later encrypt) an email message (ebXML). The message contains a Signature element that contains child elements to specify the SignedInfo, SignatureValue and KeyInfo. Also, the message contains an encrypted attachment. Question: What Java tools/apis should be used for decrypting? I would like to find some tool/api that would (automagically) instantiate objects based on whatever is included with the Signature element, so that the data (message) could be easily validated. And the other way around: Creating objects (specifying methods, signature value and keyinfo) and then outputting the xml to go into the message.

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• Can a thread call wait() on two locks at once in Java (6)

  - by Dr. Monkey

  I've just been messing around with threads in Java to get my head around them (it seems like the best way to do so) and now understand what's going on with synchronize, wait() and notify(). I'm curious about whether there's a way to wait() on two resources at once. I think the following won't quite do what I'm thinking of: synchronized(token1) { synchronized(token2) { token1.wait(); token2.wait(); //won't run until token1 is returned System.out.println("I got both tokens back"); } } In this (very contrived) case token2 will be held until token1 is returned, then token1 will be held until token2 is returned. The goal is to release both token1 and token2, then resume when both are available (note that moving the token1.wait() outside the inner synchronized loop is not what I'm getting at). A loop checking whether both are available might be more appropriate to achieve this behaviour (would this be getting near the idea of double-check locking?), but would use up extra resources - I'm not after a definitive solution since this is just to satisfy my curiosity.

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• Java ME Runnable object takes up memory although not made an instance yet

  - by user1646684

  I am facing a strange problem with memory in Java ME. here is a part of my code: int variable=1; while (true) { if (variable==2) { display = Display.getDisplay(this); MyCanvas mc = new MyCanvas(this); // MyCanvas is a runnable object mcT = new Thread(mc); // new thread for MyCanvas mc.repaint(); display.setCurrent(mc); mcT.start(); // run thread } if (variable==1) { // Do some other stuff } } The problem is that although still the variable is set to 1, so it does not come through the if (variable==2) condition the program consumes 300kB more memory than when I delete the code after condition if (variable==2). As far as I know the code should by executed and the objects shall be created only when I set variable to value 2. But it consumes the memory also when the code after condition "if (variable==2)" is not executed. Why does this happen?

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• syntax problem crating a method that returns an object (java)

  - by David

  I'm trying to create a method that will sum two timeO objects and return a new TimeO object called sum. Here is the relevant code snippet: public static TimeO add (TimeO t1, TimeO t2) { TimeO sum = new TimeO ; ... } When i try to compile it i get this error message: TimeO.java:15: '(' or '[' expected TimeO sum = new TimeO ; ^ 1 error i cant think of any reason why it would want me to open a set of parenthasies or brackets here but its possible that i dont' quite understand the syntax. Whats going wrong here?

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