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  • Is -1 a magic number? An anti-pattern? A code smell? Quotes and guidelines from authorities

    - by polygenelubricants
    I've seen -1 used in various APIs, most commonly when searching into a "collection" with zero-based indices, usually to indicate the "not found" index. This "works" because -1 is never a legal index to begin with. It seems that any negative number should work, but I think -1 is almost always used, as some sort of (unwritten?) convention. I would like to limit the scope to Java at least for now. My questions are: What are the official words from Sun regarding using -1 as a "special" return value like this? What quotes are there regarding this issue, from e.g. James Gosling, Josh Bloch, or even other authoritative figures outside of Java? What were some of the notable discussions regarding this issue in the past?

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  • Choosing a distributed shared memory solution

    - by mindas
    I have a task to build a prototype for a massively scalable distributed shared memory (DSM) app. The prototype would only serve as a proof-of-concept, but I want to spend my time most effectively by picking the components which would be used in the real solution later on. The aim of this solution is to take data input from an external source, churn it and make the result available for a number of frontends. Those "frontends" would just take the data from the cache and serve it without extra processing. The amount of frontend hits on this data can literally be millions per second. The data itself is very volatile; it can (and does) change quite rapidly. However the frontends should see "old" data until the newest has been processed and cached. The processing and writing is done by a single (redundant) node while other nodes only read the data. In other words: no read-through behaviour. I was looking into solutions like memcached however this particular one doesn't fulfil all our requirements which are listed below: The solution must at least have Java client API which is reasonably well maintained as the rest of app is written in Java and we are seasoned Java developers; The solution must be totally elastic: it should be possible to add new nodes without restarting other nodes in the cluster; The solution must be able to handle failover. Yes, I realize this means some overhead, but the overall served data size isn't big (1G max) so this shouldn't be a problem. By "failover" I mean seamless execution without hardcoding/changing server IP address(es) like in memcached clients when a node goes down; Ideally it should be possible to specify the degree of data overlapping (e.g. how many copies of the same data should be stored in the DSM cluster); There is no need to permanently store all the data but there might be a need of post-processing of some of the data (e.g. serialization to the DB). Price. Obviously we prefer free/open source but we're happy to pay a reasonable amount if a solution is worth it. In any way, paid 24hr/day support contract is a must. The whole thing has to be hosted in our data centers so SaaS offerings like Amazon SimpleDB are out of scope. We would only consider this if no other options would be available. Ideally the solution would be strictly consistent (as in CAP); however, eventual consistence can be considered as an option. Thanks in advance for any ideas.

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  • Efficiency of while(true) ServerSocket Listen

    - by Submerged
    I am wondering if a typical while(true) ServerSocket listen loop takes an entire core to wait and accept a client connection (Even when implementing runnable and using Thread .start()) I am implementing a type of distributed computing cluster and each computer needs every core it has for computation. A Master node needs to communicate with these computers (invoking static methods that modify the algorithm's functioning). The reason I need to use sockets is due to the cross platform / cross language capabilities. In some cases, PHP will be invoking these java static methods. I used a java profiler (YourKit) and I can see my running ServerSocket listen thread and it never sleeps and it's always running. Is there a better approach to do what I want? Or, will the performance hit be negligible? Please, feel free to offer any suggestion if you can think of a better way (I've tried RMI, but it isn't supported cross-language. Thanks everyone

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  • How to compile runnable jar from packages?

    - by sacamano
    Hey. My java application has got a package structure similar to this; src/com/name/app , src/com/name/app/do , src/com/name/utils/db and so on. How would I go about compiling java files in these directories in to a runnable jar? I need to package required libraries into the generated JAR (jdbc). I've always done these things in Eclipse but now I need to supply a couple of people with a way to compile the repository without the use of eclipse and I was thinking of making a makefile or a script that invokes the necessary javac pattern. Any help is greatly appreciated.

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  • Why does a looser specification in an overriding method compile after the exception specification fo

    - by Everyone
    The code below has an overridden method with a looser exception specification as compared to the method being overridden. //AnotherMain.java public class AnotherMain { public void dummyMethod( String args[] ) throws IOException{ throw new IOException(); } } //SubAnotherMain.java public class SubAnotherMain extends AnotherMain{ @Override public void dummyMethod( String[] args ) throws Exception { // To get this to compile, change the above - throws IOException, Exception super.dummyMethod(args); throw new Exception("This will not compile unless the exception specification has IOException too"); } } Afaik, the overriding method should not compile at all as the looser specification might break substitutability. Why does it compile after the original exception specification is included in the override? What have I misunderstood?

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  • Is there a recommended way to use the Observer pattern in MVP using GWT?

    - by Tomislav Nakic-Alfirevic
    I am thinking about implementing a user interface according to the MVP pattern using GWT, but have doubts about how to proceed. These are (some of) my goals: - the presenter knows nothing about the UI technology (i.e. uses nothing from com.google.*) - the view knows nothing about the model or the presenter - the model knows nothing of the view or the presenter (...obviously) I would place an interface between the view and the presenter and use the Observer pattern to decouple the two: the view generates events and the presenter gets notified. What confuses me is that java.util.Observer and java.util.Observable are not supported in GWT. This suggests that what I'm doing is not the recommended way to do it, as far as GWT is concerned, which leads me to my questions: what is the recommended way to implement MVP using GWT, specifically with the above goals in mind? How would you do it?

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  • JavaFX Threading issue - GUI freezing while method call ran.

    - by David Meadows
    Hi everyone, I hoped someone might be able to help as I'm a little stumped. I have a javafx class which runs a user interface, which includes a button to read some text out loud. When you press it, it invokes a Java object which uses the FreeTTS java speech synth to read out loud a String, which all works fine. The problem is, when the speech is being read out, the program stops completely until its completed. I'm not an expert on threaded applications, but I understand that usually if I extend the Thread class, and provided my implementation of the speech synth code inside an overridden run method, when I call start on the class it "should" create a new Thread, and run this code there, allowing the main thread which has the JavaFX GUI on to continue as normal. Any idea why this isn't the case? Thanks a lot in advance!

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  • Auto-Complete Suggestions in Source Code Editor

    - by Jim
    Hello, Most IDEs (Eclipse, Netbeans, Intelij) provide contextually smart suggestions about the current statement you're writing. We would like to do the same thing (In Java for Java). We considered tokenizing the input and building our own abstract syntax trees, but quickly realized that could be a month long project in and of its self. We also started digging through the source code for the above mentioned IDEs, but it appears (correct me if I'm wrong) that the auto-complete code is pretty tightly woven with the rest of the IDE. We're wondering if anyone knows of a relatively isolated package that we could pull into our project to provide this auto-complete functionality. Thanks!

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  • How to catch printf from a dll?

    - by Xarx
    I've got a C++ console application that uses a third-party dll (jvm.dll, indirectly) that uses printf to print various error messages (Java stacktrace). I need to catch these stacktraces to a string in order to process them further, or at least to see them printed on the console. The thing is that I see the stacktrace only when debugging my application in VisualStudio (VS 2010). When I run my application in the "normal way", i.e. from the command line, nothing is printed on the console. So VS is able to somehow interfere the java output and display it. I need to be able to do the same thing. I've already tried freopen(), but without success. Also, I've found this question on the same problem, but without a clear answer.

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  • makefile compilation problem

    - by mistique
    He I have a problem with a makefile. I have three classes. They do pretty simple stuff. One does an addition on a subtraction, and the last one will instantiate the two and simply print the resulted addition and subtraction. Now when I create my makefile, I compile my Plus.java and my Minus.java but don't know how to compile the main class because it depends on the previous two. I want to compile and run it from the makefile if it's possible. I get the above results when I try to run make: javac -g Plus.class Minus.class javac: invalid flag: Plus.class Usage: javac use -help for a list of possible options make: * [Operation.class] Error 2 I don't know how to procede, please forgive me if my question is to simple but I am new working with these stuff. I've searched many sites but with no answer.

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  • JPanel components paint-time problem

    - by Tom Brito
    I'm having a problem that when my frame is shown (after a login dialog) the buttons are not on correct position, then in some miliseconds they go to the right position (the center of the panel with border layout). When I make a SSCCE, it works correct, but when I run my whole code I have this fast-miliseconds delay to the buttons to go to the correct place. Unfortunately, I can't post the whole code, but the method that shows the frame is: public void login(JComponent userView) { centerPanel.removeAll(); centerPanel.add(userView); centerPanel.revalidate(); centerPanel.repaint(); frame.setVisible(true); } What would cause this delay to the panel layout? (I'm running everything in the EDT) -- update In my machine, this SSCCE shows the layout problem in 2 of 10 times I run it: import java.awt.BorderLayout; import javax.swing.JButton; import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.SwingUtilities; public class TEST { public static void main(String[] args) throws Exception { SwingUtilities.invokeAndWait(new Runnable() { @Override public void run() { System.out.println("Debug test..."); JPanel btnPnl = new JPanel(); btnPnl.add(new JButton("TEST")); JFrame f = new JFrame("TEST"); f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); f.getContentPane().setLayout(new BorderLayout()); f.getContentPane().add(btnPnl); f.pack(); f.setSize(800, 600); f.setVisible(true); System.out.println("End debug test!"); } }); } } The button first appers in the up-left, and then it goes to the center. Please, note that I'm understand, not just correct. Is it a java bug? --update OK, so the SSCCE don't show the problem with you that tried till now. Maybe it's my computer performance problem. But this don't answer the question, I still think Java Swing is creating new threads for make the layout behind the scenes.

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  • Longest keyword chain?

    - by pg-robban
    As I was typing some constants in Java I noticed I had used 4 keywords in a row, which Eclipse highlighted for me: public static final int. I then took a break from my regular coding and asked myself (and google with no relevant results) what the longest chain of keywords I can use and still have valid code. After a while, the best I could come up with was this method definition: public synchronized static final strictfp int a() { ... which is 6 keywords in Java. Is it possible to go 7, or even higher? What about other languages?

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  • How the simples GUI countdown is supposed to work?

    - by Roman
    I am trying to write the simples GUI countdown. I found in Internet some code but it is already too fancy for me. I am trying to keep it as simple as possible. So, I just want to have a window saying "You have 10 second left". The number of second should decrease every second from 10 to 0. I wrote a code. And I think I am close to the working solution. But I still missing something. Could you pleas help me to find out what is wrong? Here is my code: import javax.swing.*; public class Countdown { static JLabel label; // Method which defines the appearance of the window. private static void showGUI() { JFrame frame = new JFrame("Simple Countdown"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); JLabel label = new JLabel("Some Text"); frame.add(label); frame.pack(); frame.setVisible(true); } // Define a new thread in which the countdown is counting down. static Thread counter = new Thread() { public void run() { for (int i=10; i>0; i=i-1) { updateGUI(i,label); try {Thread.sleep(1000);} catch(InterruptedException e) {}; } } }; // A method which updates GUI (sets a new value of JLabel). private static void updateGUI(final int i, final JLabel label) { SwingUtilities.invokeLater(new Runnable(i,label) { public Runnable(int i, JLabel label) { this.i = i; this.label = label; } public void run() { label.setText("You have " + i + " seconds."); } }); } // The main method (entry point). public static void main(String[] args) { javax.swing.SwingUtilities.invokeLater(new Runnable() { public void run() { showGUI(); //counter.start(); } }); //counter.start(); } } And I have several concrete question about this code: Where should I place the counter.start();? (In my code I put it on 2 places. Which one is correct?) Why compiler complains about the constructor for Runnable? It says that I have an invalid method declaration and I need to specify the returned type. ADDED: I made the suggested corrections. And then I execute the code and get: Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at Worker.run(Worker.java:12) In the Worker.java in the line 12 I have: label.setText("You have " + i + " seconds.");.

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  • Write a program that allows the user to enter a string and then prints the letters of the String sep

    - by WM
    The output is always a String, for example H,E,L,L,O,. How could I limit the commas? I want the commas only between letters, for example H,E,L,L,O. import java.util.Scanner; import java.lang.String; public class forLoop { public static void main(String[] args) { Scanner Scan = new Scanner(System.in); System.out.print("Enter a string: "); String Str1 = Scan.next(); String newString=""; String Str2 =""; for (int i=0; i < Str1.length(); i++) { newString = Str1.charAt(i) + ","; Str2 = Str2 + newString; } System.out.print(Str2); } }

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  • How to parse json data from https client in android

    - by Madhan Shanmugam
    I try to fetch data from https client. Same code i used to fetch from http client. but its working fine. when i try to use Https client its not working. i am getting the following error. java.net.UnknownHostException: Host is unresolved: https client address:443 Error Log: 10-27 10:01:08.280: W/System.err(21826): java.net.UnknownHostException: Host is unresolved: https client address.com 443 10-27 10:01:08.290: W/System.err(21826): at java.net.Socket.connect(Socket.java:1037) 10-27 10:01:08.290: W/System.err(21826): at org.apache.http.conn.ssl.SSLSocketFactory.connectSocket(SSLSocketFactory.java:317) 10-27 10:01:08.310: W/System.err(21826): at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:129) 10-27 10:01:08.310: W/System.err(21826): at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164) 10-27 10:01:08.310: W/System.err(21826): at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119) 10-27 10:01:08.310: W/System.err(21826): at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:348) 10-27 10:01:08.310: W/System.err(21826): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555) 10-27 10:01:08.320: W/System.err(21826): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487) 10-27 10:01:08.320: W/System.err(21826): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465) 10-27 10:01:08.320: W/System.err(21826): at com.myfile.JSONParser.getJSONFromUrl(JSONParser.java:38) 10-27 10:01:08.320: W/System.err(21826): at com.myfile.myfile.processThread(myfile.java:159) 10-27 10:01:08.330: W/System.err(21826): at com.peripay.PERIPay$1$1.run(myfile.java:65) 10-27 10:01:08.330: E/Buffer Error(21826): Error converting result java.lang.NullPointerException 10-27 10:01:08.330: E/JSON Parser(21826): Error parsing data org.json.JSONException: A JSONObject text must begin with '{' at character 0 of

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  • New tomcat install on OSX choking on startup.

    - by baudot
    I've completed a fresh install of Tomcat6 on an OS X box that didn't have it before. It's behaved a bit strangely in other ways, but the current hang-up is that it won't start at all. In response to running startup.sh, the catalina.out log collects this error: Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/catalina/startup/Bootstrap Caused by: java.lang.ClassNotFoundException: org.apache.catalina.startup.Bootstrap at java.net.URLClassLoader$1.run(URLClassLoader.java:202) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:190) at java.lang.ClassLoader.loadClass(ClassLoader.java:307) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) at java.lang.ClassLoader.loadClass(ClassLoader.java:248) Other bits of strangeness noticed with this installation: the .sh scripts in the bin directory had no execute permission, and had to be manually chmodded. The log folder wasn't created, causing an earlier script crash. After I manually created the log folder, the startup script made it to this new error before failing. Running other scripts in the bin folder generates similar error messages involving NoClassDefFoundError. Bootstrap.java is indeed in the right place, though Bootstrap.class isn't in the same folder. For that matter, if any of the myriad class files for tomcat should have already been generated from their .java files, I haven't seen it.

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  • Consume restful webservice through web proxy

    - by Chico
    Hello, I'm trying to consume a restful webservice in java using the Apache Wink framework through my school web proxy requiring authentification ClientConfig clientConfig = new ClientConfig(); clientConfig.proxyHost("proxy.school.com"); clientConfig.proxyPort(3128); //nothing to set username and password :( RestClient client = new RestClient(clientConfig); Resource resource = client.resource("http://vimeo.com/api/v2/artist/videos.xml"); String response = resource.accept("text/plain").get(String.class); I've also tried to use the BasicAuthSecurityHandler but it seems to be used to authenticate directly to a web server, not the web proxy BasicAuthSecurityHandler basicAuthHandler = new BasicAuthSecurityHandler(); basicAuthHandler.setUserName("username"); basicAuthHandler.setPassword("password"); config.handlers(basicAuthHandler); It still fail with a HTTP 407 error code : Proxy Authentication Required. I've googled the best I could, nothing came up better to consume a webservice from a Java client through a web proxy, if someone has another idea, feel free to respond

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  • Class Methods Inheritence

    - by Roman A. Taycher
    I was told that static methods in java didn't have Inheritance but when I try the following test package test1; public class Main { /** * @param args the command line arguments */ public static void main(String[] args) { TB.ttt(); TB.ttt2(); } } package test1; public class TA { static public Boolean ttt() { System.out.println("TestInheritenceA"); return true; } static public String test ="ClassA"; } package test1; public class TB extends TA{ static public void ttt2(){ System.out.println(test); } } it printed : TestInheritenceA ClassA so do java static methods (and fields have) inheritance (if you try to call a class method does it go down the inheritance chai looking for class methods). Was this ever not the case,are there any inheritance OO languages that are messed up like that for class methods?

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  • ADF vs. EJB/Spring: Where should I invest my time?

    - by Arthur Huxley
    I am a junior Java SE developer, planning to become a Java Standard Edition professional. Which technologies/frameworks will be the smartest thing for me to learn? I will invest a lot of time and energy on the technologies that I eventually choose and it will be the basis for my carreer. I need to choose carefully. I have one question in particular regarding Oracle ADF: How can it be better than Spring or EJB 3.x? No offense to the ADF developers - and please excuse my ignorance - but is there a reason for using ADF other than locking customers to Oracle products? If ADF is an inferior technology I fear I will be making a mistake choosing to specialize in ADF.

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  • Practical programming test in interview

    - by redspike
    I have been invited to do a second interview for a company recruiting for a software engineer. This interview will consist of a 45 minute programmatic test on a laptop followed by a whiteboard presentation on the solution. This position is Java/J2EE based so I'm assuming (hoping) the test will be implemented using Java. Have you ever done anything like this? What was the nature of the problem you had to solve? What is a good way to prepare for this type of interview?

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