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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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• 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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• 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: 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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• 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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• 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: 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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• 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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• 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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• 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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• 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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• 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 input Letter

  - by xyvyre

  I'm doing an java activity that if Name start with letter A-G and Ends with Letter H-z the output is invalid heres my code: System.out.print("Enter your name: "); String str = in.readLine(); if(str.startsWith("a" )){ System.out.print("INVALID!"); } if(str.endsWith("h")){ System.out.print("INVALID!"); } This works but how can i implement letter a to g and h to z i already try this [a-g] and it not WORK!

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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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• 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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• 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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• Java synchronizing static list ?

  - by JavaUser

  Hi, In a Java class , i am having a static list so this list is shared across all the objects of this class.The business logic in this class will run periodically which is invoked by some method with out passing instance parameters.Now I want to invoke this run method based on the list(I will add some vales into this list based on JMS) ,this list may empty sometimes and after finishing the run , i am emptying this list.Now my question is , whether I need to synchronize this list or not? Also let me know is there any other way to pass value in one object instance(Thread1) to other object instance (Thread2) other than having Static variable(static list)? Thx

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• Java Trusting ssl CA

  - by LuigiEdlCarno

  I guess I am out of ideas here. I am trying to consume a web service in java which has an ssl certificate. I createt a a keystore file in which I have added the certificate. The file lies in my project folder. I imported it using: System.setProperty("javax.net.ssl.keyStore", "folder\\keystore.jks"); System.setProperty("javax.net.ssl.keyStorePassword", "SECRET"); Apparently, the web service call checks the keystore because when giving a wrong path to the file the application throws an exception when invoking the WS, not when setting the system property. Anyway, when giving the correct path to the keystore file, I still get AxisFault faultCode: {http://xml.apache.org/axis/}HTTP faultSubcode: faultString: (401)Authorization Required Someone told me I had to trust the CA, before any of this would work. How do I do this?

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• Aligning all panel components java

  - by destructo_gold

  I am using the BoxLayout layout manager in java, and have aligned a bunch of components: myLabel.setAlignmentX(Component.LEFT_ALIGNMENT); myTextBox.setAlignmentX(Component.LEFT_ALIGNMENT); myButton.setAlignmentX(Component.LEFT_ALIGNMENT); ... I have a lot of components, and this seems over the top. Is there a shorthand way? I tried the following, but setAlignmentX isn't a method inside Component? for (Component c : personPanel.getComponents()) { c.setAlignmentX(Component.LEFT_ALIGNMENT); }

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• Poll for pressed buttons in Java

  - by directedition

  I have a WorldWind application build based on the Java SDK. It has a great event handler for detecting when you click on objects, but I've run into a snag. While I can click on and select individual objects, I can't determine if the user is pressing the control key while they click (if they want to select multiple objects). I can implement event handlers for both the mouse and the keyboard, but I can't for the life of me figure out how to tie the two together. How could I make my mouse listener poll the system for a list of currently depressed keys?

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• Cant communicate with server in java

  - by cerq

  i m trying to write server to client program but i cant communicate with server in java. Below there is code block in my main. InetAddress addr = InetAddress.getLocalHost(); ipAddress = "78.162.206.164"; ServerSocket serverSocket = new ServerSocket(0); String randomStringForPlayerName = RandomStringGenerator.generateRandomString(); baseForReqOpp += ipAddress + " " + serverSocket + " " + randomStringForPlayerName; Socket socket = new Socket(host,2050); socket.setSoTimeout(100); in = new BufferedReader(new InputStreamReader(socket.getInputStream())); out = new PrintWriter(socket.getOutputStream()); out.write(baseForReqOpp); out.flush(); System.out.println(in.read()); i know there is no problem in server code and all the ports in communication are ok. But i cant read anything from server. What can be the problem?

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• Threads in JAVA

  - by theband

  I was today asked in an interview over the Thread concepts in JAVA? The Questions were... What is a thread? Why do we go for threading? A real time example over the threads. Can we create threads in Spring framework service class. Can flex call a thread? I did not answer any questions apart from definition of Thread, that too i just learnt from internet. Can anyone explain me clearly over this.

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• how to export a 2D table in java

  - by kate

  hello i would like to ask you about the 2D tables in java!!my code is this an i would like to make a system out in order t see the registrations in mytable citylink can anyone help me? int i=0; while(i<=citylink.length){ for(Xml polh_is:fetchsite.child("site").child("poleis").children("polh")){ //url if((polh_is.string("name")=="")||(polh_is.content()==""))//attribute error += "Error in polh: name is - " + polh_is.string("name") + " with url - " + polh_is.content() + " -.\n"; else for(int j=0; j<citylink.length; j++){ citylink[j][0]=HtmlMethods.removeBreaks(polh_is.string("name")); citylink[j][1]=HtmlMethods.removeBreaks(polh_is.string("with url -"+polh_is.content() +"-.\n")); i++; } }

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• Passing a generic class to a java function?

  - by rodo

  Is it possible to use Generics when passing a class to a java function? I was hoping to do something like this: public static class DoStuff { public <T extends Class<List>> void doStuffToList(T className) { System.out.println(className); } public void test() { doStuffToList(List.class); // compiles doStuffToList(ArrayList.class); // compiler error (undesired behaviour) doStuffToList(Integer.class); // compiler error (desired behaviour) } } Ideally the List.class and ArrayList.class lines would work fine, but the Integer.class line would cause a compile error. I could use Class as my type instead of T extends Class<List> but then I won't catch the Integer.class case above.

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