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  • What should Java programmer learn?

    - by Dieter
    Hi, I code only for 3 years now, I came thru C/C++, Delphi, SQL, VBA but I mostly code in Java. I do 90% GUIs, atm with Java swing. But time changes, so I have few questions : Should I switch to web development from GUIs? If GUIs, is C# and WPF suitable ? Should I learn .NET (C#,asp.net) or continue with Java (learn Spring, hibernate, JSP, JSF, JPA) ? What is faster to learn? Finish Java or start .NET Should I really consider using something other than Java/.NET ? Think of job opportunities. Thanx

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  • Java: Read POST data from a socket on an HTTP server

    - by danpalmer
    I have a website (python/django) that needs to use a load of Java resources that may or may not be on the same server. Therefore I am writing a mini webserver in Java that will receive a request and then when processing is finished, POST some data back to a url on the site. I have got the java code receiving connections on sockets and responding with some simple HTML. My problem is that I will POST data to the Java server and that code needs to act on the data. How do I go about reading the data that is posted in the HTML request, if it is even possible. If not, is there any other way you would do this. If you think I am going about this in completely the wrong way then please tell me and I will consider another method, but after conversing with some Java developers, this seemed like the best way for what I was doing. Thanks

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  • XML-RPC with java

    - by Mona
    hi, I'm developing a server in XML-RPC using Java , but when i compile it , i get this error ServeurSomDiff.java:33: cannot find symbol symbol : method addHandler(java.lang.String,java.lang.String) location: class org.apache.xmlrpc.webserver.WebServer server.addHandler("SOMDIFF",new ServeurSomDiff ()); here 's my server : import java.util.Hashtable; import org.apache.xmlrpc.webserver.*; public class ServeurSomDiff { public ServeurSomDiff (){ } public Hashtable sumAndDifference (int x, int y) { Hashtable result = new Hashtable(); result.put("somme", new Integer(x + y)); result.put("difference", new Integer(x - y)); return result; } public static void main (String [] args) { try { WebServer server = new WebServer(8000); server.addHandler("SOMDIFF",new ServeurSomDiff()); server.start(); System.out.println("Serveur lance sur http://localhost:8000/RPC2"); } catch (Exception exception) {System.err.println("JavaServer: " + exception.toString()); } } } any ideas on how to fix this . thanks

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  • Java: initialization problem with private-final-int-value and empty constructor

    - by HH
    $ javac InitInt.java InitInt.java:7: variable right might not have been initialized InitInt(){} ^ 1 error $ cat InitInt.java import java.util.*; import java.io.*; public class InitInt { private final int right; InitInt(){} public static void main(String[] args) { // I don't want to assign any value. // just initialize it, how? InitInt test = new InitInt(); System.out.println(test.getRight()); // later assiging a value } public int getRight(){return right;} } Initialization problem with Constructor InitInt{ // Still the error, "may not be initialized" // How to initialise it? if(snippetBuilder.length()>(charwisePos+25)){ right=charwisePos+25; }else{ right=snippetBuilder.length()-1; } }

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  • Catching java.lang.OutOfMemoryError

    - by dotsid
    Documentation for java.lang.Error says: An Error is a subclass of Throwable that indicates serious problems that a reasonable application should not try to catch But as java.lang.Error is subclass of java.lang.Throwable I can catch this type of throwable. I understand why this is not good idea to catch this sort of exceptions. As far as I understand, if we decide to caught it, the catch handler should not allocate any memory by itself. Otherwise OutOfMemoryError will be thrown again. So, my question is: is there any real word scenarios when catching java.lang.OutOfMemoryError may be a good idea? if we catching java.lang.OutOfMemoryError how can we sure that catch handler doesn't allocate any memory by itself (any tools or best practicies)? Thanks a lot.

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  • Should Java IOException have been an unchecked RuntimeException?

    - by Derek Mahar
    Do you agree that the designers of Java class java.io.IOException should have made it an unchecked run-time exception derived from java.lang.RuntimeException instead of a checked exception derived only from java.lang.Exception? I think that class IOException should have been an unchecked exception because there is little that an application can do to resolve problems like file system errors. However, in When You Can't Throw An Exception, Elliotte Rusty Harold claims that most I/O errors are transient and so you can retry an I/O operation several times before giving up: For instance, an IOComparator might not take an I/O error lying down, but — because many I/O problems are transient — you can retry a few times, as shown in Listing 7: Is this generally the case? Can a Java application correct I/O errors or wait for the system to recover? If so, then it is reasonable for IOException to be checked, but if it is not the case, then IOException should be unchecked so that business logic can delegate handling this exception to a separate system error handler.

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  • Shipping Java code with data baked into the .jar

    - by Andrew
    I need to ship some Java code that has an associated set of data. It's a simulator for a device, and I want to be able to include all of the data used for the simulated records in the one .JAR file. In this case, each simulated record contains four fields (calling party, called party, start of call, call duration). What's the best way to do that? I've gone down the path of generating the data as Java statements, but IntelliJ doesn't seem particularly happy dealing with a 100,000 line Java source file! Is there a smarter way to do this? In the C#/.NET world I'd create the data as a separate file, embed it in the assembly as a resource, and then use reflection to pull that out at runtime and access it. I'm unsure of what the appropriate analogy is in the Java world. FWIW, Java 1.6, shipping for Solaris.

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  • google maps export driving directions to kml file - java geogoogle

    - by maiky
    Hi Sorry at first for my poor grammar. I am writing a program in Java using geogoogle (Google Geocoder Java API) http://geo-google.sourceforge.net/ I need from two specific points to get the walking directions between these points and also these info to be exported in a KML file. Do you know how can I do it from Java? Is there an API that I can use? Perhaps making a call from the java program to google and handle the result - but how can it be done? Thanks in advance. PS. Google gives this functionality as i saw here http://www.gringod.com/2008/02/26/save-google-maps-driving-directions/ but I need all these to be called from Java.

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  • Socksifying a Java ServerSocket - how to approach

    - by Thorbjørn Ravn Andersen
    I would like to have a Java program running on network A have a ServerSocket living on another network B through a proxy. I have played with a SOCKS5 proxy (which works) but it appears that all the proxy facilities in Java only work with client connections, not with ServerSockets (no constructor taking a Proxy argument). Asking Google gives much hay and few needles. What is the approach I should take to get this running? If a specific client is better than a generic SOCKS or web proxy then fine, but it needs to be Java (that leaves sshd out). Target JVM is preferrably Java 5, and then Java 6.

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  • Controlling maximum Java standalone running in Linux

    - by Gnanam
    Hi, We've developed a Java standalone program. We've configured in our Linux (RedHat ES 4) cron schedule to execute this Java standalone every 10 minutes. Each standalone may sometime take more than 1 hour to complete, or sometime it may complete even within 5 minutes. My problem/solution I'm looking for is, the number of Java standalones executing at any time should not exceed, for example, 5 threads. So, for example, before even a Java standalone/thread starts, if there are already 5 threads running, then this thread should not be started; otherwise this would indirectly start creating OutOfMemoryError problems. How do I control this? I would also like to make this 5 thread as configurable. Other Information: I've also configured -Xms and -Xmx heap size settings. Is there any tool/mechanism by which we can control this? I also heard about Java Service Wrapper. What is this all about?

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  • Java: design problem with final-value and empty constructor

    - by HH
    $ javac InitInt.java InitInt.java:7: variable right might not have been initialized InitInt(){} ^ 1 error $ cat InitInt.java import java.util.*; import java.io.*; public class InitInt { private final int right; // Design Problem? // I feel the initialization problem is just due to bad style. InitInt(){} InitInt{ // Still the error, "may not be initialized" // How to initialise it? if(snippetBuilder.length()>(charwisePos+25)){ right=charwisePos+25; }else{ right=snippetBuilder.length()-1; } } public static void main(String[] args) { InitInt test = new InitInt(); System.out.println(test.getRight()); } public int getRight(){return right;} } Partial Solutions and Suggestions use "this" to access methods in the class, instead of creating empty constructor change final to non-final with final field value: initialize all final values in every constructor remove the empty constructor, keep your code simple and clean

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  • Where do Java Applets live?

    - by Wendi Peters
    I'm trying to figure out where java Applets that I run from the browser live. I'm using Firefox 3.0 on Windows XP with Java 1.6 if that makes any difference. From the Java Control Panel on the toolbar, I can access "Temporary Internet Files - Settings" to find the Java cache. From there I can show the resources and see a file called "dws2010066.dat". Does this resource correspond to a file on disk? I did a search in the Java cache/my whole computer and came up empty handed.

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  • How to get java to recognize symbolic links under cygwin

    - by Keith Randall
    Here's a very simple java program to print the first line of a file: import java.io.* public class test { public static void main(String[] args) throws IOException { System.out.print(new BufferedReader(new FileReader(args[0])).readLine()); } } When I run this program under cygwin and pass it the name of a symbolic link, it prints the contents of the symbolic link, not the target of that link: $ echo foo > testfile $ ln -s testfile symlink_to_testfile $ java test testfile foo $ java test symlink_to_testfile !<symlink> ?t e s t f i l e How do I convince java to follow the symlink? I was hoping there was something simpler than implementing the redirect myself.

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  • How to stop java application using a shell script

    - by Fernando Moyano
    I have a shell script, which is run under a opensuse linux, that starts a java application (under a jar), the script is: #!/bin/sh #export JAVA_HOME=/usr/local/java #PATH=/usr/local/java/bin:${PATH} #---------------------------------# # dynamically build the classpath # #---------------------------------# THE_CLASSPATH= for i in `ls ./lib/*.jar` do THE_CLASSPATH=${THE_CLASSPATH}:${i} done #---------------------------# # run the application # #---------------------------# java -server -Xms512M -Xmx1G -cp ".:${THE_CLASSPATH}" com.package.MyApp > myApp.out 2>&0 & This script is working fine. Now, what I want, is to write a script to kill gracefully this app, something that allows me to kill it with the -15 argument from Linux kill command. The problem, is that there will be many java applications running on this server, so I need to specifically kill this one. Any help? Thanks in advance, Fernando

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  • Java compiler error: "cannot find symbol" when trying to access local variable

    - by HH
    $ javac GetAllDirs.java GetAllDirs.java:16: cannot find symbol symbol : variable checkFile location: class GetAllDirs System.out.println(checkFile.getName()); ^ 1 error $ cat GetAllDirs.java import java.util.*; import java.io.*; public class GetAllDirs { public void getAllDirs(File file) { if(file.isDirectory()){ System.out.println(file.getName()); File checkFile = new File(file.getCanonicalPath()); }else if(file.isFile()){ System.out.println(file.getName()); File checkFile = new File(file.getParent()); }else{ // checkFile should get Initialized at least HERE! File checkFile = file; } System.out.println(file.getName()); // WHY ERROR HERE: checkfile not found System.out.println(checkFile.getName()); } public static void main(String[] args) { GetAllDirs dirs = new GetAllDirs(); File current = new File("."); dirs.getAllDirs(current); } }

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  • What is the most efficient Java Collections library?

    - by dehmann
    What is the most efficient Java Collections library? A few years ago, I did a lot of Java and had the impression back then that trove is the best (most efficient) Java Collections implementation. But when I read the answers to the question "Most useful free Java libraries?" I noticed that trove is hardly mentioned. So which Java Collections library is best now? UPDATE: To clarify, I mostly want to know what library to use when I have to store millions of entries in a hash table etc. (need a small runtime and memory footprint).

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  • Java RMI : connection refused

    - by mihsathe
    I have written following code for the client of RMI. But getting java.rmi.ConnectException: Connection refused to host: localhost; nested exception is: java.net.ConnectException: Connection refused: connect code : import java.rmi.*; import java.net.*; import java.rmi.registry.*; class client { public static void main(String [] ars) { Iface serv; Registry r; String serveraddr = ars[0]; String serverport = ars[1]; String text = "Hey jude"; System.out.println("Sending" + text); try{ r = LocateRegistry.getRegistry( serveraddr, (new Integer(serverport)).intValue() ); serv = (Iface) r.lookup("rmi://server"); serv.receive(text); } catch(Exception e){ System.out.println(e); } } }

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  • java.io.IOException: Invalid argument

    - by Luixv
    Hi I have a web application running in cluster mode with a load balancer. It consists in two tomcats (T1, and T2) addressing only one DB. T2 is nfs mounted to T1. This is the only dofference between both nodes. I have a java method generating some files. If the request runs on T1 there is no problem but if the request is running on node 2 I get an exception as follows: java.io.IOException: Invalid argument at java.io.FileOutputStream.close0(Native Method) at java.io.FileOutputStream.close(FileOutputStream.java:279) The corresponding code is as follows: for (int i = 0; i < dataFileList.size(); i++) { outputFileName = outputFolder + fileNameList.get(i); FileOutputStream fileOut = new FileOutputStream(outputFileName); fileOut.write(dataFileList.get(i), 0, dataFileList.get(i).length); fileOut.flush(); fileOut.close(); } The exception appears at the fileOut.close() Any hint? Luis

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  • Sanitize json input to a java server

    - by morgancodes
    I'm using json to pass data between the browser and a java server. I'm using Json-lib to convert between java objects and json. I'd like to strip out susupicious looking stuff (i.e "doSomethingNasty().) from the user input while converting from json to java. I can imagine several points at which I could do this: I could examine the raw json string and strip out funny-looking stuff I could look for a way to intercept every json value on its way into the java object, and look for funny stuff there. I could traverse my new java objects immediately after reconstitution from json, look for any fields that are Strings, and stripp stuff out there. What's the best approach? Are there any technologies built for this this task that I tack tack on to what I have already?

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  • why do we all learn and study java or .net or why java or .net are popular?

    - by tadeze
    My question to be clear is why do we all need to learn java or .net(C#) , still java or .net are more popular than delphi or c++ and even there are lot of resource,articles or books compared to c++ or delphi about java and .net. However, I heard majority, if I am right about 80% of software are developed using c++ or delphi in the software industry. so, why do we bother about other languages specifically about the cosmopolitan languages such as java or .net in education as well as for job interview. Although, still I know the elegance of java and .net, their safe code execution,fully objected oriented behavior ...etc, but still according to the statics they are not preferred on software develpement as a primary language mainly because of their execution time compared to c++ or delphi. So my question are why do they choose them for jobs or educational purpose and everything else? why do we lose our time learning these language if we are forced to use the other languages in the industry?

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  • How to compile these 2 java files correctly?

    - by user198729
    I'm following the steps here, it's basically : Compile the DataSource and LiveStream classes: javac -d . DataSource.java LiveStream.java Run using JMStudio: java JMStudio screen://0,0,160,120/10 But when I compile them, got lots of errors like javax.media doesn't exist and so on. Here's the directory structure: D:\>dir 2010-06-11 22:25 <DIR> . 2010-06-11 22:25 <DIR> .. 2010-06-11 22:25 3,730 DataSource.java 2010-06-11 22:25 6,860 LiveStream.java Can someone give more detailed steps how to set up the environment correctly to compile correctly?

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  • java.lang.UnsupportedClassVersionError in eclipse

    - by Derek
    Hi all, I am not a Java programmer really, so I am posting this question. The exception is being thrown java.lang.UnsupportedClassVersionError in my main class in an eclipse project. If I comment out the imports that this class has, it compiles and runs fine. If I put the imports back in, it does not work. Does this mean that the libraries I am importing were compiled with a newer or older version of java than I have? when i do java -version on the system i get 1.5_07 I could've sworn this was actually working last week, but maybe some setting in eclipse got tweaked? Is the Java Build Path in eclipse what I need to look for to check the JRE and compiler versions?

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  • Create Java method from a string?

    - by drozzy
    Is it possible in Java, to declare a method with a string instead of an identifier? For example can I do something like the following: class Car{ new Method("getFoo", { return 1+1; }); } //Use it Car car = new Car(); car.getFoo(); EDIT: I am adding a Purpose WHY I need this. In order to not hardcode method names when using Jersey and it's UriBuilder, which requires a method name: https://jsr311.dev.java.net/nonav/releases/1.1/javax/ws/rs/core/UriBuilder.html See path() method with signature: public abstract UriBuilder path(java.lang.Class resource, java.lang.String method) throws java.lang.IllegalArgumentException I hope my question is clear, if not - let me know and I can clarify it.

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  • ANTLR - Embedding Java code, evaluate before or after?

    - by wvd
    Hello all, I'm writing a simple scripting language on top of Java/JVM, where you can also embed Java code using the {} brackets. The problem is, how do I parse this in the grammar? I have two options: 1] Allow everything to be in it, such as: [a-z|a-Z|0-9|_|$], and go on 2] Get an extra java grammar and use that grammar to parse that small code (is it actually possible and efficient?) Since option 2] is basically a double-check since when evaluating java code it's also being checked. Now my last question is -- is way that can dynamically execute java code also with objects which have been created at runtime? Thanks, William van Doorn

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  • Swing object: first setText() gets "stuck" when using Mac Java SE 6

    - by Tim
    Hi there, I am a Java newbie trying to maintain an application that works fine under J2SE 5.0 (32- and 64-bit) but has a very specific problem when run under Java SE 6 64-bit: [Tims-MPB:~] tlynch% java -version java version "1.6.0_15" Java(TM) SE Runtime Environment (build 1.6.0_15-b03-226) Java HotSpot(TM) 64-Bit Server VM (build 14.1-b02-92, mixed mode) The application is cross-platform and reportedly works correctly on Java SE 6 under Windows, though I haven't been able to verify that myself. The program uses a JTextField for some text entry and a JLabel to indicate the text to be entered. The first time the showDialog() method is called to set the label text and display the dialog, it works correctly, but subsequent calls all result in the display of the label from the initial invocation rather than the one most recently specified via setText(). public void showDialog(String msgText) { System.out.println("set ChatDialog: " + msgText); jLabel1.setText(msgText); jLabel1.repaint(); // I added this; it didn't help System.out.println("get ChatDialog: " + jLabel1.getText()); super.setVisible(true); } [the full text of the class is provided below] The added printlns validate that expected text is passed to the label's setText() method and is confirmed by retrieving it using getText(), but what shows up on the screen/GUI is always the text from the very first time the method was called for the object. A similar issue is observed with a JTextArea used to label another dialog box. These problem are consistent across multiple Mac systems running Java SE 6 under OS 10.5.x and 10.6.x, but they are never observed when one reverts to J2SE 5.0. If there is some background information pertinent to this problem that I have omitted, please let me know. Any insights or advice appreciated. package gui; import java.awt.*; import java.awt.event.KeyEvent; import javax.swing.*; // Referenced classes of package gui: // MyJPanel, ChatDialog_jTextField1_keyAdapter, WarWindow public class ChatDialog extends JDialog { public ChatDialog(JFrame parent, WarWindow w) { super(parent, true); text = ""; borderLayout1 = new BorderLayout(); jPanel1 = new MyJPanel(); borderLayout2 = new BorderLayout(); jPanel2 = new MyJPanel(); jPanel3 = new MyJPanel(); jLabel1 = new JLabel(); jTextField1 = new JTextField(); warWindow = w; try { jbInit(); } catch(Exception exception) { System.out.println("Problem with ChatDialog init"); exception.printStackTrace(); } return; } public String getText() { return text; } void jTextField1_keyPressed(KeyEvent e) { int id = e.getKeyCode(); switch(id) { case 10: // '\n' text = jTextField1.getText(); setVisible(false); break; } } private void jbInit() throws Exception { setLocation(232, 450); setSize(560, 60); setModal(true); setResizable(false); setUndecorated(true); getContentPane().setLayout(borderLayout1); jPanel1.setLayout(borderLayout2); jPanel2.setMinimumSize(new Dimension(10, 20)); jPanel2.setPreferredSize(new Dimension(10, 20)); jLabel1.setPreferredSize(new Dimension(380, 15)); jLabel1.setHorizontalAlignment(0); jLabel1.setText("Chat Message"); jTextField1.setPreferredSize(new Dimension(520, 21)); jTextField1.setRequestFocusEnabled(false); jTextField1.addKeyListener(new ChatDialog_jTextField1_keyAdapter(this)); getContentPane().add(jPanel1, "Center"); jPanel1.add(jPanel2, "North"); jPanel2.add(jLabel1, null); jPanel1.add(jPanel3, "Center"); jPanel3.add(jTextField1, null); } public void setVisible(boolean b) { jTextField1.setText(""); super.setVisible(b); } public void showDialog(String msgText) { System.out.println("set ChatDialog: " + msgText); jLabel1.setText(msgText); jLabel1.repaint(); // I added this; it didn't help System.out.println("get ChatDialog: " + jLabel1.getText()); super.setVisible(true); } void this_keyPressed(KeyEvent e) { int id = e.getKeyCode(); switch(id) { case 10: // '\n' System.exit(88); break; } } BorderLayout borderLayout1; BorderLayout borderLayout2; JLabel jLabel1; JPanel jPanel1; JPanel jPanel2; JPanel jPanel3; JTextField jTextField1; String text; WarWindow warWindow; }

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