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• R from java with no graphics: is it worth moving to JRI

  - by LH

  I have a system set up that's been happily running R from a java servlet, spawning processed & hooking into the process's stdin, stdout, and stderr streams, as in the second andwer to this question. After a system upgrade (that included glibc), the input is no longer reaching the R process.* Until now, 'R --vanilla --slave -f [file] ...' was working fine for me. I also have no swing dependencies right now, so I'm somewhat reluctant to add them. (I may actually not be able to add swing dependencies; am I right that using REngine automatically brings swing in? The examples import all of swing.) Are there advantages to switching to JRI? What changes would I need to make to my R script? (It currently reads from stdin and writes to stdout). I'm not finding the provided examples terribly helpful for how to use JRI in this situation. Thanks for your help & comments. *I can't even tell if the problem is data being written too soon or too late, but that's a separate issue/question; if I move to JRI I'm hoping it all becomes moot.

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• Java Map question

  - by user552961

  I have one Map that contains some names and numbers Map<String,Integer> abc = new TreeMap<String,Integer>(); It works fine. I can put some values in it but when I call it in different class it gives me wrong order. For example: I putted abc.put("a",1); abc.put("b",5); abc.put("c",3); some time it returns the order (b,a,c) and some time (a,c,b). What is wrong with it? Is there any step that I am missing when I call this map?

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• Problem with underscore(_) in Collections.binarySearch (Java)

  - by Alex Cheng

  Hi all. Problem: I am using Java Tutorials™ sourcecode for this. This is the source code. I tried this: --following with another section of sorted words-- words.add("count"); words.add("cvs"); words.add("dce"); words.add("depth"); --following with another section of sorted words-- and it works perfectly. However when I use this: --just a section of sorted words-- words.add("count"); words.add("cvs"); words.add("dce_iface"); words.add("dce_opnum"); words.add("dce_stub_data"); words.add("depth"); --following with another section of sorted words-- It does show dce_iface when I type dce, but when I type _ then following with o or s it shows me something else like dce_offset where the offset comes from words.add("fragoffset"); somewhere in the list. What can I do to solve this problem? Thank you in advance.

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• Many-to-Many Relationship (with properties) in Google App Engine for Java

  - by rvandervort

  I understand from the official documentation on unowned relationships that the app must use sets of Key objects on either side of the relationship. This makes perfect sense. Coming from many years of RDBM-style programming, though, I'm pretty confused about how I can model properties of that relationship itself. For example, if I have entities Category and Entry in my many-to-many relationship and would like to persist a dateAdded property, or some other data that are only relevant when both sides of the relationship are known. I suppose it would be possible to create a third class : CategoryEntry that links the two, but this seems like a kludge. What is the proposed way to model this kind of situation ?

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• How to approach socket programming between C# -> Java (Android)

  - by Alex

  I've recently knocked up a server/client app for Windows & Android that allows one to send a file from Windows to an android phone over a socket connection. It works great for a single file but trying to send multiple files over in a single stream is causing me problems. I've also realised that aside from the binary data, I will need to send messages over the socket to indicate error states and other application messages. I have little experience with network programming and and wondering what is the best way forward. Basically the C# server side of the app just goes into a listening state and uses Socket.SendFile to transmit the file. On Android I use the standard Java Socket.getInputStream() to receive the file. That works great for a single file transfer, but how should I handle multiple files and error/messaging information? Do I need to use a different socket for each file? Should I be using a higher level framework to handle this or can I send everything over the single socket? Any other suggestions for frameworks or learning materials?

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• More than one unique key for HashMap problem (Java)

  - by Alex Cheng

  This question is a continuation of this thread: In short: To solve my problem, I want to use Map<Set<String>, String>. However, after I sort my data entries in Excel, remove the unnecessary parameters, and the following came out: flow content ==> content content flow content ==> content depth distance flow content ==> content depth within flow content ==> content depth within distance flow content ==> content within flow content ==> content within distance I have more than one unique key for the hashmap if that is the case. How do I go around this... anyone have any idea? I was thinking of maybe Map<Set <String>, List <String>> so that I can do something like: Set <flow content>, List <'content content','content depth distance','content depth within ', ..., 'content within distance'> But because I am parsing the entries line by line I can't figure out the way how to store values of the same repeated keys (flow content) into the same list and add it to the map. Anyone have a rough logic on how can this be done in Java? Thanks in advance.

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• java regex for alpha and spaces is including [ ] \

  - by JayAvon

  This is my regex for my JTextField to not be longer than x characters and to not include anything other than letters or spaces. For some reason it is allowing [ ] and \ characters. This is driving me crazy. Is my regex wrong?? package com.jayavon.game.helper; import java.awt.Toolkit; import javax.swing.text.AttributeSet; import javax.swing.text.BadLocationException; import javax.swing.text.PlainDocument; public class CharacterNameCreationDocument extends PlainDocument { private static final long serialVersionUID = 1L; private int limit; public CharacterNameCreationDocument(int limit) { super(); this.limit = limit; } public void insertString(int offset, String str, AttributeSet attr) throws BadLocationException { if (str == null || (getLength() + str.length()) > limit || !str.matches("[a-zA-z\\s]*")){ Toolkit.getDefaultToolkit().beep(); return; } else { super.insertString(offset, str, attr); } } }

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• Java: Efficient Equivalent to Removing while Iterating a Collection

  - by Claudiu

  Hello everyone. We all know you can't do this: for (Object i : l) if (condition(i)) l.remove(i); ConcurrentModificationException etc... this apparently works sometimes, but not always. Here's some specific code: public static void main(String[] args) { Collection<Integer> l = new ArrayList<Integer>(); for (int i=0; i < 10; ++i) { l.add(new Integer(4)); l.add(new Integer(5)); l.add(new Integer(6)); } for (Integer i : l) { if (i.intValue() == 5) l.remove(i); } System.out.println(l); } This, of course, results in: Exception in thread "main" java.util.ConcurrentModificationException ...even though multiple threads aren't doing it... Anyway. What's the best solution to this problem? "Best" here means most time and space efficient (I realize you can't always have both!) I'm also using an arbitrary Collection here, not necessarily an ArrayList, so you can't rely on get.

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• singleton pattern in java- lazy Intialization

  - by flash

  public static MySingleton getInstance() { if (_instance==null) { synchronized (MySingleton.class) { _instance = new MySingleton(); } } return _instance; } 1.is there a flaw with the above implementation of the getInstance method? 2.What is the difference between the two implementations.? public static synchronized MySingleton getInstance() { if (_instance==null) { _instance = new MySingleton(); } return _instance; } I have seen a lot of answers on the singleton pattern in stackoverflow but the question I have posted is to know mainly difference of 'synchronize' at method and block level in this particular case.

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• java Sockets and Threads Problem

  - by vs4vijay

  I am doin a Some Socket Programing Stuff in Java.. Here i have created a button(Create Server)..and when i click it ,it starts server...but i want to change the button name to (Stop Server) after Starting the server... so i did this.. but when i press start server it starts and the button name remains the same... and when a client gets connected to it ,then it change the name to stop server... tell me whats the wrong with this code?? Here is My a SomePart Of Code... public void actionPerformed(ActionEvent ex) { if(ex.getActionCommand() == "CreateServer") { bt1.setText("Stop Server"); bt2.setEnabled(false); b5.setText("Server Started On Port " + tf2.getText()); System.out.println("Server started 1"); create(Integer.parseInt(tf2.getText())); //my func. to create server System.out.println("Server started 2"); } } and my create() fucn. contains some sockets and thread...so tell me what the problem...

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• Zoom in Java Swing application

  - by Shirky

  Hi there, I am looking for ways to zoom in a Java Swing application. That means that I would like to resize all components in a given JPanel by a given factor as if I would take an screenshot of the UI and just applied an "Image scale" operation. The font size as well as the size of checkboxes, textboxes, cursors etc. has to be adjusted. It is possible to scale a component by applying transforms to a graphics object: protected Graphics getComponentGraphics(Graphics g) { Graphics2D g2d=(Graphics2D)g; g2d.scale(2, 2); return super.getComponentGraphics(g2d); } That works as long as you don't care about self-updating components. If you have a textbox in your application this approach ceases to work since the textbox updates itself every second to show the (blinking) cursor. And since it doesn't use the modified graphics object this time the component appears at the old location. Is there a possibility to change a components graphics object permanently? There is also a problem with the mouse click event handlers. The other possibility would be to resize all child components of the JPanel (setPreferredSize) to a new size. That doesn't work for checkboxes since the displayed picture of the checkbox doesn't change its size. I also thought of programming my own layout manager but I don't think that this will work since layout managers only change the position (and size) of objects but are not able to zoom into checkboxes (see previous paragraph). Or am I wrong with this hypothesis? Do you have any ideas how one could achieve a zoomable Swing GUI without programming custom components? I looked for rotatable user interfaces because the problem seems familiar but I also didn't find any satisfying solution to this problem. Thanks for your help, Chris

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• Help with string equality in Java

  - by annayena

  The following function accepts 2 strings, the 2nd (not 1st) possibly containing *'s (asterisks). An * is a replacement for a string (empty, 1 char or more), it can appear appear (only in s2) once, twice, more or not at all, it cannot be adjacent to another * (ab**c), no need to check that. public static boolean samePattern(String s1, String s2) It returns true if strings are of the same pattern. It must be recursive, not use any loops, static or global variables. Also it's prohibited to use the method equals in the String class. Can use local variables and method overloading. Can use only these methods: charAt(i), substring(i), substring(i, j), length(). Examples: 1: TheExamIsEasy; 2: "The*xamIs*y" ---> true 1: TheExamIsEasy; 2: "Th*mIsEasy*" ---> true 1: TheExamIsEasy; 2: "*" ---> true 1: TheExamIsEasy; 2: "TheExamIsEasy" ---> true 1: TheExamIsEasy; 2: "The*IsHard" ---> FALSE I am stucked on this question for many hours now! I need the solution in Java please kindly help me.

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• Trouble understanding the semantics of volatile in Java

  - by HungryTux

  I've been reading up about the use of volatile variables in Java. I understand that they ensure instant visibility of their latest updates to all the threads running in the system on different cores/processors. However no atomicity of the operations that caused these updates is ensured. I see the following literature being used frequently A write to a volatile field happens-before every read of that same field . This is where I am a little confused. Here's a snippet of code which should help me better explain my query. volatile int x = 0; volatile int y = 0; Thread-0: | Thread-1: | if (x==1) { | if (y==1) { return false; | return false; } else { | } else { y=1; | x=1; return true; | return true; } | } Since x & y are both volatile, we have the following happens-before edges between the write of y in Thread-0 and read of y in Thread-1 between the write of x in Thread-1 and read of x in Thread-0 Does this imply that, at any point of time, only one of the threads can be in its 'else' block(since a write would happen before the read)? It may well be possible that Thread-0 starts, loads x, finds it value as 0 and right before it is about to write y in the else-block, there's a context switch to Thread-1 which loads y finds it value as 0 and thus enters the else-block too. Does volatile guard against such context switches (seems very unlikely)?

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• Timer in Java swing

  - by Yesha

  I'm trying to replace Thread.sleep with a java swing timer as I hear that is much better for graphics. Before, I had something set up like this, but it was interfering with the graphics. while(counter < array.size){ Thread.sleep(array.get(counter).startTime); //do first task Thread.sleep(array.get(counter).secondTime); //do second task Thread.sleep(array.get(counter).thirdTime); //do third task counter++ } Now, I'm trying to replace each Thread.sleep with one of these and then I have the actual events that happen after this, but it does not seem to be waiting at all. int test = array.get(counter).time; ActionListener taskPerformer = new ActionListener(){ public void actionPerformed(ActionEvent evt){ } }; Timer t = new Timer(test, taskPerformer); t.setRepeats(false); t.start(); Basically, how do I ensure that the program will wait without giving it any code to execute inside of the timer? Thank you!

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• Learning Java Swing (GUI builder or not?)

  - by Paul

  Well I know basic Java and wanted to learn Swing so of course looked at the Sun website first, where this tutorial is. I was going to start it but realised it relied heavily on NetBeans, which I'm not sure about. I'm not sure because it's learning that I want to acheive, not a nice looking program. So I thought using NetBeans like this would be great once I know it, but I don't want to be building things without a clue what's going on underneath, and of course this could also cause problems later. My first question is is this the right way to do it, should I try not to rely on an IDE heavily? Looking through questions on the site most people recommend using the Sun tutorial, and I've only seen one answer that agrees with what I'm thinking, and they linked to this resource which looks promising. Or perhaps I'm getting the wrong idea of the Sun tutorial, perhaps it doesn't rely on the IDE, it just seemed like that. My second question is, if you agree with me, what resources (apart from the one above) would you recommend? Thanks for your answers.

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• Java: howto write equals() shorter

  - by erikb

  I get headaches when I have to write nearly 10 lines of code to say 2 Objects are equal, when their type is equal and both's attribute is equal. You can easily see that in this way of writing the number of lines increase drastically with your number of attributes. public class Id implements Node { private String name; public Id(String name) { this.name = name; } public boolean equals(Object o) { if (o == null) return false; if (null == (Id) o) return false; Id i = (Id) o; if ((this.name != null && i.name == null) || (this.name == null && i.name != null)) return false; return (this.name == null && i.name == null) || this.name.equals(i.name); } }

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• getting duplicate array output - java

  - by dowln

  Hello, Can someone could be kind and help me out here. Thanks in advance... My code below outputs the string as duplicates. I don't want to use Sets or ArrayList. I am using java.util.Random. I am trying to write a code that checks if string has already been randomly outputted and if it does, then it won't display. Where I am going wrong and how do I fix this. public class Worldcountries { private static Random nums = new Random(); private static String[] countries = { "America", "Candada", "Chile", "Argentina" }; public static int Dice() { return (generator.nums.nextInt(6) + 1); } public String randomCounties() { String aTemp = " "; int numOfTimes = Dice(); int dup = 0; for(int i=0 ; i<numOfTimes; i++) { // I think it's in the if statement where I am going wrong. if (!countries[i].equals(countries[i])) { i = i + 1; } else { dup--; } // and maybe here aTemp = aTemp + countries[nums.nextInt(countries.length)]; aTemp = aTemp + ","; } return aTemp; } } So the output I am getting (randomly) is, "America, America, Chile" when it should be "America, Chile".

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• what does "do" do here? (java)

  - by David

  I saw this bit of code on the interents somewhere. I'm wondering what thedo is for. public class LoopControl { public static void main(String[] args) { int count = 0; do { if(count % 2 == 0) { for(int j = 0; j < count; j++) { System.out.print(j+1); if(j < count-1) System.out.print(", "); } System.out.println(); } count++; } while(count <= 5); } }

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• Java - Display % of upload done

  - by tr-raziel

  I have a java applet for uploading files to server. I want to display the % of data sent but when I use ObjectOutputStream.write() it just writes to the buffer, does not wait until the data has actually been sent. How can I achieve this. Perhaps I need to use thread synchronization or something. Any clues would be most helpful. This is the code I'm using right now: try{ for(File file : ficheiros){ FileInputStream stream = new FileInputStream (file); int bytesRead1 = 0;; int off1 = 0; int len1 = 100000; if(file.length() < 100000) len1 = new Long(file.length()).intValue(); byte[] bytes1 = new byte[len1]; while (off1 < file.length()) { bytes1 = new byte[len1]; if((file.length() - off1) < len1){ len1 = (new Long(file.length()).intValue() - off1); bytes1 = new byte[len1]; } if((bytesRead1 = stream.read(bytes1)) != -1){ //I want this to block until all data has been sent outputToServlet.write(bytes1, 0, bytesRead1 ); System.out.println("off1: " + off1); off1 = off1 + len1; outputToServlet.flush(); } sent += len1; if(sent>totalLength) sent = (int)totalLength; updateFeedback(sent,totalLength,false);//calls method to display % } updateFeedback(-1,-1,true); } }catch(Exception e){ e.printStackTrace(); } Thanks

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• Javascript enabled but not enabled in Firefox browser

  - by k s subramanisn

  I had installed Java ii icedtea-6-jre-cacao 6b24-1.11.5-0ubuntu1~12.04.1 Alternative JVM for OpenJDK, using Cacao ii icedtea-6-jre-jamvm 6b24-1.11.5-0ubuntu1~12.04.1 Alternative JVM for OpenJDK, using JamVM ii openjdk-6-jre-headless 6b24-1.11.5-0ubuntu1~12.04.1 OpenJDK Java runtime, using Hotspot JIT (headless) ii openjdk-6-jre-lib 6b24-1.11.5-0ubuntu1~12.04.1 OpenJDK Java runtime (architecture and had installed addon in Firefox browser QuickJava 1.8.0. And still keep getting message Javascript enabled, but Java is not enabled in Firefox browser while trying to use on-line bill payment facility.

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• Failed to create symbolic link to keytool

  - by mt0s

  Keytool is /usr/bin/keytool and points to /etc/alternatives/keytool which in turn points to /usr/lib/jvm/java-6-openjdk-i386/jre/bin/keytool. Now I have installed java version 1.7.0_45 so I need to change keytool to the new path : /usr/lib/jvm/jdk1.7.0_45/jre/bin/keytool I tried deleting the /usr/bin/keytool with rm -rf and then adding a new link like : sudo ln -s /usr/bin/keytool /usr/lib/jvm/jdk1.7.0_45/jre/bin/keytool but what I get is ln: failed to create symbolic link `/usr/lib/jvm/jdk1.7.0_45/jre/bin/keytool': File exists I also tried : sudo update-alternatives --config keytool There is only one alternative in link group keytool: /usr/lib/jvm/java-6-openjdk-i386/jre/bin/keytool Nothing to configure. update-alternatives: warning: forcing reinstallation of alternative /usr/lib/jvm/java-6-openjdk-i386/jre/bin/keytool because link group keytool is broken. but doesn't works too. Any suggestions ? Thank you

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• Turn On Your PC/Computer Programmatically / Automatically –Wake On LAN ( WOL ) Over Internet- Wake O

  Start your Computer by C , C++ , JAVA , .NET ..

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• Android “open for embedded”? Must-read Ars Technica article

  - by terrencebarr

  A few days ago ars technica published an article “Google’s iron grip on Android: Controlling open source by any means necessary”. If you are considering Android for embedded this article is a must-read to understand the severe ramifications of Google’s tight (and tightening) control on the Android technology and ecosystem. Some quotes from the ars technica article: “Android is open – except for all the good parts“ “Android actually falls into two categories: the open parts from the Android Open Source Project (AOSP) … and the closed source parts, which are all the Google-branded apps” “Android open source apps … turn into abandonware by moving all continuing development to a closed source model.” “Joining the OHA requires a company to sign its life away and promise to not build a device that runs a competing Android fork.” “Google Play Services is a closed source app owned by Google … to turn the “Android App Ecosystem” into the “Google Play Ecosystem” “You’re allowed to contribute to Android and allowed to use it for little hobbies, but in nearly every area, the deck is stacked against anyone trying to use Android without Google’s blessing“ Compare this with a recent Wired article “Oracle Makes Java More Relevant Than Ever”: “Oracle has actually opened up Java even more — getting rid of some of the closed-door machinations that used to be part of the Java standards-making process. Java has been raked over the coals for security problems over the past few years, but Oracle has kept regular updates coming. And it’s working on a major upgrade to Java, due early next year.” Cheers, – Terrence Filed under: Embedded, Mobile & Embedded Tagged: Android, embedded, Java Embedded, Open Source

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• Why not Green Threads?

  - by redjamjar

  Whilst I know questions on this have been covered already (e.g. http://stackoverflow.com/questions/5713142/green-threads-vs-non-green-threads), I don't feel like I've got a satisfactory answer. The question is: why don't JVM's support green threads anymore? It says this on the code-style Java FAQ: A green thread refers to a mode of operation for the Java Virtual Machine (JVM) in which all code is executed in a single operating system thread. And this over on java.sun.com: The downside is that using green threads means system threads on Linux are not taken advantage of and so the Java virtual machine is not scalable when additional CPUs are added. It seems to me that the JVM could have a pool of system processes equal to the number of cores, and then run green threads on top of that. This could offer some big advantages when you have a very number large of threads which block often (mostly because current JVM's cap the number of threads). Thoughts?

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• JavaOne Latin America Underway

  - by Tori Wieldt

  JavaOne Latin America started officially today, but lots of networking has already happened. Last night some JUG leaders, Java Champions, and members of the Oracle Java development and marketing teams had dinner together. The conversation ranged from the new direction of JavaFX to how to improve JUG attendance. Maricio Leal shared the idea some Brazilian JUGs have of putting Java Evangelists and experts on a boat and having them visit JUGs on cities along the Amazon river.  We discussed ideas, and shared dessert pizza. It was the perfect community get together! If you see Brazilian Java Man Bruno Souza, ask him what he is bringing to the party.Today, at JavaOne Latin America, all the sessions were full, and developers were spilling into the hallways. Session content was selected with the help of 14 Java thought leaders from Latin America. JavaOne Program Committee Chair, Sharat Chander, said "I'm thrilled that at this JavaOne over half of the content is coming from the community." Between sessions, developers take advantage of the Oracle Technology Network lounge to grab a snack and use their laptops.  OTN LoungeIt promises to be a great JavaOne.

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