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• Java ServerSocketChannel SocketChannel (Callback)

  - by ikurtz

  I am trying to learn Java. I would like to implement a simple networked connect 4 game as well as a chat feature. I want my network logic to be non blocking so after much study I found that SocketChannel is what I am after regrading my needs. What has not made sense still is the lack of CallBack functions in SocketChannels.. Like one finds in C#. My query for this time is: How do I deliver the data received to the Chat or Game form (JFrame)? Some guidance is most welcome.

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• How to implement low pass filter using java

  - by chai

  Hello Everyone, I am trying to implement a low pass filter in Java. My requirement is very simple,I have to eliminate signals beyond a particular frequency (Single dimension). Looks like Butterworth filter would suit my need. Now the important thing is that CPU time should be as low as possible. There would be close to a million sample the filter would have to process and our users don't like waiting too long. Are there any readymade implementation of Butterworth filters which has optimal algorithms for filtering. Regards, Chaitannya

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• Java: ListA.addAll(ListB) fires NullPointerException?

  - by HH

  The err part is Capitalized in the code, it also comes in foreaching. Because of the abstract list, it cannot be initialized, declaration is in a static field. The lists have the same type. import java.util.*; public class Test { public static final List<String> highPrio = Arrays.asList("*","/"); public static List<String> ops; public static void main(String[] args) { //ERROR HERE, why do it throw nullPointer? ops.addAll(highPrio); for(String s : ops) { System.out.println(s); } } }

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• Adding Timestamp to Java's GC messages in Tomcat 6

  - by ripper234

  I turned on Java's GC log options -XX:+PrintGC -XX:+PrintGCTimeStamps -XX:+PrintGCDetails Which print out these messages to standard output (catalina.out): 314.884: [CMS-concurrent-mark-start] 315.014: [CMS-concurrent-mark: 0.129/0.129 secs] [Times: user=0.14 sys=0.00, real=0.13 secs] 315.014: [CMS-concurrent-preclean-start] 315.016: [CMS-concurrent-preclean: 0.003/0.003 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 315.016: [CMS-concurrent-abortable-preclean-start] 332.055: [GC 332.055: [ParNew: 17128K->84K(19136K), 0.0017700 secs] 88000K->70956K(522176K) icms_dc=4 , 0.0018660 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] CMS: abort preclean due to time 352.253: [CMS-concurrent-abortable-preclean: 0.023/37.237 secs] [Times: user=0.78 sys=0.02, real=37.23 secs] How can I make these log lines appear with an actual timestamp (including date) instead of these numbers, which presumably mean "time since JVM started" ?

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• How to implement a unit converter in java

  - by Mohit Deshpande

  How could I possibly implement a unit converter in Java??? I was thinking of having a abstract base class: public abstract class Unit { ... public void ConvertTo(Unit unit); } Then having each class like Meter Kilometer Inch Centimeter Millimeter ... derive from that base Unit class. All the units of length would be in a package called com.unitconverter.distance, then a package, com.unitconverter.energy, for energy etc. etc. So is this the best way to implement a unit converter? Or is there a better or more easier way?

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• Thread Jobs in Java

  - by Bragaadeesh

  Hi, I want to spawn 200 threads simultaneously in Java. What I'm doing right now is running into a loop and creating 200 threads and starting them. After these 200 gets completed, I want to spawn another 200 set of threads and so on. The gist here is that the first 200 threads I spawned need to be FINISHED before spawning the next set. I tried the code below, but its not working for(int i=0;i<200;i++){ Thread myThread = new Thread(runnableInstance); myThread.start(); } for(int i=0;i<200;i++){ Thread myThread = new Thread(runnableInstance); myThread.start(); } Note: I have intentionally put the for loop Twice, but the desired effect I intend is not happening simply because the second for loop is executed before the first set of threads end their execution. Please advise

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• Java - jar with librairies included

  - by kozher

  I am currently trying to make a Jar with all my librairies included. What I have done. I have created folders like this : - main folder - class (which contain all my classes) - ressources (containing all my librairies : mongo, jedis...) - MANIFEST.MF My main class is named process. My manifest is like this : Main-Class: processEAN Class-Path: ressources\commons-pool-1.5.6.jar ressources\jedis-2.0.0.jar resources\mongo-2.6.3.jar class - I have generated the JAR with this command : jar cvmf MANIFEST.MF processEAN.jar class/*.class ressources/*.jar My problem : When executing the JAR I have still the message "Exception in thread "main" java.lang.NoClassDefFoundError: processEAN" Any ideas ? Thanks

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• [java] How to get ALL the information from a socket

  - by raven

  Hello, I'll begin this question with the claim that I have read the java networking guide before asking you. I do not understand how to READ the socket and get all the info summed up into a string. the socket might contains more than 1 line [trying to make a chat]. Please do no refer me to any other site unless it clearly states "this exact line does this.." because I failed to understand what this code part does BufferedReader stdIn = new BufferedReader( new InputStreamReader(System.in)); String userInput; while ((userInput = stdIn.readLine()) != null) { out.println(userInput); System.out.println("echo: " + in.readLine()); } Please, I just want to make a loop that will receive information from a socket, get all the content together into one string [I also want it to know where to add another line]. Thanks allot for anyone who helps, I have been trying to get an answer from tuts for hours and just failed to understand!

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• strange bug - how to pause a java program?

  - by TerraNova993

  I'm trying to: display a text in a jLabel, wait for two seconds, then write a new text in the jLabel this should be simple, but I get a strange bug: the first text is never written, the application just waits for 2 seconds and then displays the final text. here is the example code: private void testButtonActionPerformed(java.awt.event.ActionEvent evt) { displayLabel.setText("Clicked!"); // first method with System timer /* long t0= System.currentTimeMillis(); long t1= System.currentTimeMillis(); do{ t1 = System.currentTimeMillis(); } while ((t1 - t0) < (2000)); */ // second method with thread.sleep() try { Thread.currentThread().sleep(2000); } catch (InterruptedException e) {} displayLabel.setText("STOP"); } with this code, the text "Clicked!" is never displayed. I just get a 2 seconds - pause and then the "STOP" text. I tried to use System timer with a loop, or Thread.sleep(), but both methods give the same result.

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• Comparing Each Character in Java String

  - by user2760357

  I am a beginner at java, and I am trying to create two strings and compare each character. If there is a matching character or characters, the code has to print out the length of each string, without the matching characters. For example, if one string is "super," and the other is "perfect," the program should interpret the strings as superfect, and print out 9 However, if there is no matching part, like pencil and eraser, the code should printout 12, which is the length of two strings combined. Right now, I am having a problem with comparing each character, since I tried to use if(input_word.compareToIgnoreCase(input_word2) != 0) but it only compared the string as a whole.. any suggestion? Thank you for your efforts

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• record mouse movements, clicks and keyboard input with Java or C++

  - by Joe

  I want to be able to record mouse movements, clicks and keyboard input from a user. It would be great if it was a cross platform solution. I'd like to get back something like this (pseudo code): mouse moved to 500, 500 mouse double clicked mouse moved to 800, 300 mouse left clicked keyboard typed "Hello World" Does either C++ or Java have any classes that can do this? If I was using C++, I would probably working with the QT framework. Edit: I should have said this originally, but I want to record the movements and clicks outside of the applications gui, so on the desktop too.

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• Making commercial Java software

  - by roddik

  Hi. I intend to make some software to be sold over internet. I've only created open-source before, so I have really no idea of how to protect it from being cracked and distributed as warez. Bearing in mind that I know like two programms that aren't either cracked or not really useful I decided that the only more or less reliable way may look like this: Connect to a server and provide licensing info and some sort of hardware summary info If everything is fine, the server returns some crucial missing parts of the program bound to that certain pc along with the usage limit of say 2 days That crucial stuff is not saved to hard drive, so it is downloaded every time the program starts, if the programm runs more than 2 days, data is downloaded again If the same info is used from different computers, suspend the customer account What do you think about this? It may seem a bit to restrictive, but I'd better make less sales at first then eventually see my precious killer app downloaded for free. Anyways, first I need some basic theory/tutorials/guides about how to ensure that user only uses a certain Java app if he has paid for it, so please suggest some. Thanks

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• How do I instantiate Class Dynamically in Java?

  - by kunjaan

  I have the class name stored in a property file. I know that the classes store will implement IDynamicLoad. How do I instantiate the class dynamically? Right now I have Properties foo = new Properties(); foo.load(new FileInputStream(new File("ClassName.properties"))); String class_name = foo.getProperty("class","DefaultClass"); //IDynamicLoad newClass = Class.forName(class_name).newInstance(); Does the newInstance only load compiled .class files? How do I load a Java Class that is not compiled?

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• Print number series in java

  - by user1898282

  I have to print the series shown below in java: ***1*** **2*2** *3*3*3* 4*4*4*4 My current implementation is: public static void printSeries(int number,int numberOfCharsinEachLine){ String s="*"; for(int i=1;i<=number;i++){ int countOfs=(numberOfCharsinEachLine-(i)-(i-1))/2; if(countOfs<0){ System.out.println("Can't be done"); break; } for(int j=0;j<countOfs;j++){ System.out.print(s); } System.out.print(i); for(int k=1;k<i;k++){ System.out.print(s); System.out.print(i); } for(int j=0;j<countOfs;j++){ System.out.print(s); } System.out.println(); } } But there are lot of for loops, so I'm wondering whether this can be done in a better way or not?

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• Java - Set Color by switch case function

  - by user369150

  I want to set the color of the TextView by the function getcolorss. I tried a lot of different ways but i cant get in it. Please help me i think the solution is easy. import java.awt.*; import android.graphics.Color; public class test extends Activity { TextView text1 = (TextView) findViewById(R.id.text1); text1.setTextColor(getcolorss(1)); public Color getcolorss(int x) { switch(x) { case 1: return Color.BLUE; case 2: return Color.RED; } } }

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• Use of class definitions inside a method in Java

  - by Bragaadeesh

  Hi public class TestClass { public static void main(String[] args) { TestClass t = new TestClass(); } private static void testMethod(){ class TestMethodClass{ int a; int b; int c; } TestMethodClass testMethodClass = new TestMethodClass(); } } I found out that the above piece of code is perfectly legal in Java. I have the following questions. What is the use of ever having a class definition inside a method? Will a class file be generated for TestMethodClass Its hard for me to imagine this concept in an Object Oriented manner. Having a class definition inside a behavior. Probably can someone tell me with equivalent real world examples. Thanks

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• How to get value from Java object

  - by JSF User

  I have this Java object private List<NewAccountObj> dataList; public class NewAccountObj { private int userid; public NewAccountObj(int userid) { this.userid = userid; } public int getUserid() { return userid; } public void setUserid(int userid) { this.userid = userid; } public List<NewAccountObj> getdataList() { return dataList; } What is the proper way to access a value from the object? Is this correct? <h:inputText id="userid" value="#{NewAccountController.dataList.userid}" validator="#{ValidatorAccountController.validateUserID}" autocomplete="off"> <f:ajax event="blur" render="useridvalidator" /> </h:inputText> Is there any other solution?

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• JAVA bytecode optimization

  - by Idob

  This is a basic question. I have code which shouldn't run on metadata beans. All metadata beans are located under metadata package. Now, I use reflection API to find out whether a class is located in the the metadata package. if (newEntity.getClass().getPackage().getName().contains("metadata")) I use this If in several places within this code. The question is: Should I do this once with: boolean isMetadata = false if (newEntity.getClass().getPackage().getName().contains("metadata")) { isMetadata = true; } C++ makes optimizations and knows that this code was already called and it won't call it again. Does JAVA makes optimization? I know reflection API is a beat heavy and I prefer not to lose expensive runtime.

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• How to draw a filled circle in Java?

  - by Roman

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

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• Method to concatenate 2 Strings in Java

  - by GooF

  I have a method in Java that concatenates 2 Strings. It currently works correctly, but I think it can be written better. public static String concat(String str1, String str2) { String rVal = null; if (str1 != null || str2 != null) { rVal = ""; if (str1 != null) { rVal += str1; } if (str2 != null) { rVal += str2; } } return rVal; } Here are some of the requirements: If both str1 and str2 are null, the method returns null If either str1 or str2 is null, it will just return the not null String If str1 and str2 are not null, it will concatenate them It never adds "null" to the result Can anyone do this with less code?

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• Replace String pattern in Java

  - by Hirantha

  I have the following string "value=\"\\d{4}((((0[1-9])|(1[0-2]))((0[1-9])|([12]\\d)|(3[01]))?)?|(\\-(((0[1-9])|(1[0-2]))(\\-((0[1-9])|([12]\\d)|(3[01])))?)?)?)d{4}" There I want to replace all the occurrences of "{" with NCHAR(0x7B) "}" with NCHAR(0x7D). An the content in-between "{ }" should remain unchanged: Ex: \\d{4} after replacing -> NCHAR(0x7B) 4 NCHAR(0x7D). Is there a way to do this using Regular Expressions in Java?. Anyway, this can be done processing the whole string using string operations.

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• Updating a database periodically with Java

  - by MSR

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

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• find number range in java

  - by Gandalf StormCrow

  How to get number range in java? for instance how can verify is the number 2389 within 10 numbers from 2400. its not but 2389 is. Ok here is the rephrase : Number 1000 is the range number 990 is comming in the loop, I return true because the between 990 and 1000 is 10 numbers diference. In comes the next number 989 range is always 1000, I return false because the between 989 and 1000 is 11 numbers diference. In comes the next number 1013 range is always 1000, I return false because the between 1013 and 1000 is 13 numbers diference.

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• Embedded Java Databases for Large Data Sets

  - by ExAmerican

  I would like to port a PHP/MySQL-based client/server application to be a standalone desktop application written in Java. The database has grown to be fairly large, with several tables with hundreds of thousands of rows. I expect these could grow to over a million entries for certain tables. What embedded database would best handle this? HSQLDB and Sqlite seem to be the obvious choices, though I'm guessing there are others out there as well. My main priorities are the ability to perform queries on large amounts of data efficiently (this thread seems to confirm Sqlite can handle this) and the ease with which I can import old data from MySQL (I remember HSQLDB being kind of a pain for that). Note: I am aware that similar questions comparing embedded databases have been posted before (for example here and here) but as my priorities differ somewhat from most applications considering the large data migration I thought it justified a new question.

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• How to pass sockets created to another Java Process

  - by whoi

  Hi; We have an application which creates many sockets which belongs to its thread, By design if this application somehow fails, all threads stop which is not wanted. So to overcome this issue, each thread must be separated from the main application, if one of the threads fails, the other ones should be running. One thing in our mind is to pass created socket to another java process, so what is the correct way? An other approach also is welcome? Waiting for your suggestions...

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