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• Efficiency of Java code with primitive types

  - by super89

  Hello! I want to ask which piece of code is more efficient in Java? Code 1: void f() { for(int i = 0 ; i < 99999;i++) { for(int j = 0 ; j < 99999;j++) { //Some operations } } } Code 2: void f() { int i,j; for(i = 0 ; i < 99999;i++) { for(j = 0 ; j < 99999;j++) { //Some operations } } } My teacher said that second is better, but I can't agree that opinion.

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• Making your class an event source in Java

  - by Crystal

  I'm making a custom button in Java that has two states, mousePressed, and mouseReleased. At the same time, if I wanted to reuse this button, so that other event listeners can register with it, are these the appropriate steps I should do: override addActionListener(ActionListener action) override removeActionListener(ActionListener action) have a private variable like List <ActionListener> list = new List <ActionListener>() to keep track of when events get added and some sort of function with for loop to run all the actions: public void runListeners() { for (ActionListener al : list) { al.actionPerfomed; } } I'm not really sure if this is the way you can do it or if there are other things I am missing. Like does my custom class have to be implements ActionListener? Thanks.

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• Manipulating and comparing floating points in java

  - by Praneeth

  In Java the floating point arithmetic is not represented precisely. For example following snippet of code float a = 1.2; float b= 3.0; float c = a * b; if(c == 3.6){ System.out.println("c is 3.6"); } else { System.out.println("c is not 3.6"); } actually prints "c is not 3.6". I'm not interested in precision beyond 3 decimals (#.###). How can I deal with this problem to multiply floats and compare them reliably? Thanks much

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• Convert Word doc to HTML programmatically in Java

  - by kaychaks

  Hi, I need to convert a Word document into HTML file(s) in Java. The function will take input an word document and the output will be html file(s) based on the number of pages the word document has i.e. if the word document has 3 pages then there will be 3 html files generated having the required page break. I searched for open source/non-commercial APIs which can convert doc to html but for no result. Anybody who have done this type of job before please help. Thanks

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• Count the number of lines in a Java String

  - by Simon Guo

  Need some compact code for counting the number of lines in a string in Java. The string is to be separated by \r or \n. Each instance of those newline characters will be considered as a separate line. For example, "Hello\nWorld\nThis\nIs\t" should return 4. The prototype is private static int countLines(String str) {...} Can someone provide a compact set of statements? I have solution at here but it is too long, I think. Thank you.

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• Java String Replace and null characters

  - by praspa

  Testing out someone elses code (of course it was ...) , I noticed a few JSP pages printing funky non-ascii characters. Taking a dip into the source I found this tidbit. // remove any periods from first name e.g. Mr. John --> Mr John firstName = firstName.trim().replace('.','\0'); Does replacing a character in a String with a null character even work in Java? I know that '\0' will terminate a c-string. Would this be the culprit to the funky characters? Thanks PR

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• Problem with "scopes" of variables in try catch blocks in Java

  - by devoured elysium

  Could anyone explain me why in the last lines, br is not recognized as variable? I've even tried putting br in the try clause, setting it as final, etc. Does this have anything to do with Java not support closures? I am 99% confident similar code would work in C#. private void loadCommands(String fileName) { try { final BufferedReader br = new BufferedReader(new FileReader(fileName)); while (br.ready()) { actionList.add(CommandFactory.GetCommandFromText(this, br.readLine())); } } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { if (br != null) br.close(); //<-- This gives error. It doesn't // know the br variable. } } Thanks

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• Can you dynamically resize a java.util.concurrent.ThreadPoolExecutor while it still has tasks waitin

  - by Edward Shtern

  I'm working with a java.util.concurrent.ThreadPoolExecutor to process a number of items in parallel. Although the threading itself works fine, at times we've run into other resource constraints due to actions happening in the threads, which made us want to dial down the number of Threads in the pool. I'd like to know if there's a way to dial down the number of the threads while the threads area actually working. I know that you can call setMaximumPoolSize() and/or setCorePoolSize(), but these only resize the pool once threads become idle, but they don't become idle until there are no tasks waiting in the queue.

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• Java/Swing offscreen rendering (Cobra HTMLPanel -> BufferedImage) Problem: Component doesn't finish

  - by Alterscape

  I'm trying to render the contents of a the Java/Swing Cobra HTML renderer to an offscreen BufferedImage, for use elsewhere in my app: slideViewPanel.setDocument(document, rendererContext); BufferedImage test = new BufferedImage(300,300,BufferedImage.TYPE_INT_RGB); Graphics g = test.getGraphics(); slideViewPanel.paint(g); The resulting image in g shows a partially rendered page -- sometimes the contents of the HTMLFrame before the new document was set; sometimes a half-rendered version of the new document. I gather this is because Cobra's setDocument method just schedules the document for re-rendering, but I'm stepping through in the debugger and I don't see a second thread to do re-rendering. Anyone have any insight into what might be happening here?

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• Performance intensive string splitting and manipulation in java

  - by juhanic

  What is the most efficient way to split a string by a very simple separator? Some background: I am porting a function I wrote in C with a bunch of pointer arithmetic to java and it is incredibly slow(After some optimisation still 5* slower). Having profiled it, it turns out a lot of that overhead is in String.split The function in question takes a host name or ip address and makes it generic: 123.123.123.123-*.123.123.123 a.b.c.example.com-*.example.com This can be run over several million items on a regular basis, so performance is an issue.

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• creative way for implementing Data object with it's corespanding buisness logic class in java

  - by ekeren

  I have a class that need to be serialized (for both persistentcy and client-server communication) for simplicity reasons lets call the classes Business a BusinessData and I prefix for their Interfaces. All the getter and setter are delegated from Business class to BusinessData class. I thought about implementing IBusinessData interface that will contain all the getter and setters and IBusiness interface that will extend it. I can either make Business extend BuisnessData so I will not need to implement all getter and setter delegates, or make some abstract class ForwardingBusinessData that will only delegate getter and setters. Any of the above option I loose my hierarchy freedom, does any of you have any creative solution for this problem... I also reviewed DAO pattern: http://java.sun.com/blueprints/patterns/DAO.html

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• Java: I can't interact with my JFrame

  - by Wooooo

  Hi, I have a java application (1.4.2) that uses 2 JFrames. The first is Modal=true and appears on top of the second JFrame. The first JFrame allows the user to "open" a file. Once the file is ready to be displayed, the JFrame is set to setModal=false, and this.dispose() 'd of. This leaves only the second JFrame on the screen. However, I can't interact with it. The code does not throw any errors and appears to run perfectly fine. BUT I can;t interact with the second JFrame. The ONLY way to exit the JFrame is to hit the stop button on my development envirnment. I literally cannot stop the JFrame by clicking the close button, because I can't even interact with that portion of the JFrame. Any thoughts?

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• Java Spring 3.0 MVC Annotation vs COC. Whats the preferred method in the Java community?

  - by Athens

  I am using Spring's MVC framework for an application I'm hosting on Google's App Engine. So far, my controllers are registered via the @Controller annotation; however, prior to getting into Spring, I evaluated ASP.net MVC 2 which requires no configuration and is based on convention. Is convention over configuration (COC) the current and preferred method in the Java community to implement MVC with Spring. Also, this may be a result of my limited knowledge so far but i noticed that i could only instantiate my Controllers the required constuctor injection if i use the COC method via the ControllerClassNameHandlerMapping. For instance the following controller bean config will fail if i use the defaultannotationhandlermapping. <bean id="c" class="com.domain.TestController"> <constructor-arg ref="service" /> </bean> <bean id="service" class="com.domain.Service" /> My com.domain.TestController controller works fine if i use ControllerClassNameHandlerMapping/COC but it results in an error when i use defaultannotationhandlermapping/Annotations.

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• Java: constructing a file from a URI?

  - by AP257

  I need to obtain a File object from a URI, working in Java, but keep getting a length of zero - though I know the file size is not zero. I need the File object to pass to another constructor. I'm not sure if it's because I'm constructing it in the wrong way? Here's my code: File videoFile = new File(videoURI.getPath()); if (videoFile == null) { Log.d(LOG_TAG, "File not found!"); return false; } Log.d(LOG_TAG, "about to upload, filepath: " + videoFile.getPath()); Log.d(LOG_TAG, "File length: " + String.valueOf(videoFile.length())); The log output doesn't spit out 'File not found!', and prints a non-null path, but shows a length of 0.

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• Searching through Collections in Java

  - by Click Upvote

  I have a java properties file containing a key/value pair of country names and codes. I will load the contents of this file into a Collection like List or HashMap. Then, I want users to be able to search for a country, e.g if they type 'Aus' in a textbox and click submit, then I want to search through the collection I have, containing a key/value pair of country codes/names (e.g AUS=Australia), and return those countries which are found matching. Is there any more efficient way of doing this, other than looping through the elements of the collection and using charAt()?

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• Connecting Java se Client to Glassfish

  - by Henrik Bierbum Bacher

  We are having some difficulties connecting our Java SE standalone client with the EJB module deployed on a remote GlassFish server. Pointers to how we are supposed to connect our client would be appreciated. The client code we currently has to get the initial context: props.setProperty("org.omg.CORBA.ORBInitialHost", "*remotehost*"); props.setProperty("org.omg.CORBA.ORBInitialPort", "portNumber"); javax.naming.InitialContext ic = new javax.naming.InitialContext(props); *We have tried several different port numbers; 3700, 7676, 8080.. The closest we are getting, got us the error: "Error in GIOP magic". I read that jms are using port 7676 as a broker port for a bunch of dynamically generated ports, but can't figure out how to specify those ports in order to create proper port-forwards.

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• Java: IDE working well with Maven War overlays

  - by Thorbjørn Ravn Andersen

  We have a Java EE 6 web application which is fully mavenized, and we use the Maven "war overlay" facility to add customer specific files, and which currently runs in Glassfish 3.1. We have traditionally used Eclipse for development, but I have found that the combination of Maven processing and War deployments may not be optimal in terms of deployment times, and that the mavenization allows us to use any IDE with good Maven support. Therefore is Eclipse the best bet for our particular scenario (maven war overlays - glassfish, and debugging it) or is e.g. Netbeans or IntelliJ better? Please, back opinions with actual experiences, thanks.

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• About local Final varibles in java

  - by Sathish

  In java Program, parameters which is defined as String in method declaration.But in method definition it is accessed as final String variable. Whether it'll lead to some issues (like security, memory problem)? For Example: Method Declaration join(String a,String b); Method definition public void join(final String a,final String b) { Authenticator au = new Authenticator(){ public PasswordAuthentication getPasswordAuthentication(){ return new PasswordAuthentication(a,b)} }; } Please help for me and clarify my doubts. Thanks in advance P.S. I;m accessing a and b as final variable because i've to use it in the inner class.

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• Com port don't work in java

  - by ?????? ?????

  Does't work with java... don't sent message to my microchip. please help public static void main(String[] args) { SerialPort serialPort = new SerialPort("COM1"); try { serialPort.openPort(); serialPort.setParams(9600, 8, 1, 0); serialPort.setParams(SerialPort.BAUDRATE_9600, SerialPort.DATABITS_8, SerialPort.STOPBITS_1, SerialPort.PARITY_NONE); serialPort.writeBytes("Test"); readBytes(), ???? ?? ??????? ?????? byte[] buffer = serialPort.readBytes(10); //????????? ???? serialPort.closePort(); } catch (SerialPortException ex) { System.out.println(ex); } } } byte[] Write "[@B********" Star is a random number.

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• Java multiline string

  - by skiphoppy

  Coming from Perl, I sure am missing the "here-document" means of creating a multi-line string in source code: $string = <<"EOF" # create a three line string text text text EOF In Java I have to have cumbersome quotes and plus signs on every line as I concatenate my multiline string from scratch. What are some better alternatives? Define my string in a properties file? Edit: Two answers say StringBuilder.append() is preferable to the plus notation. Could anyone elaborate as to why they think so? It doesn't look more preferable to me at all. I'm looking for away around the fact that multiline strings are not a first-class language construct, which means I definitely don't want to replace a first-class language construct (string concatenation with plus) with method calls. Edit: To clarify my question further, I'm not concerned about performance at all. I'm concerned about maintainability and design issues.

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• Jython java call throws exception asking for 2 args when only one arg is coded

  - by clutch

  I have an Java method I want to call within my Jython servlet running on tomcat5. It looks like this: @SuppressWarnings("unchecked") public School loadByName(String name) { List<School> school; school = getHibernateTemplate().find("from " + getPersistentClass().getName() + " where name = ?", name); return uniqueResult(school); } I call it in Jython using: foobar = SchoolDAOHibernate.loadByName('Univeristy') It throws an error that says loadByName() expects 2 args; got 1. What other argument could it be looking for?

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• Workaround for abstract attributes in Java

  - by deamon

  In Scala I would write an abstract class with an abstract attribute path: abstract class Base { val path: String } class Sub extends Base { override val path = "/demo/" } Java doesn't know abstract attributes and I wonder what would be the best way to work around this limitation. My ideas: a) constructor parameter abstract class Base { protected String path; protected Base(String path) { this.path = path; } } class Sub extends Base { public Sub() { super("/demo/"); } } b) abstract method abstract class Base { // could be an interface too abstract String getPath(); } class Sub extends Base { public String getPath() { return "/demo/"; } } Which one do you like better? Other ideas? I tend to use the constructor since the path value should not be computed at runtime.

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• Replicating Java's DecimalFormat in C#

  - by Frank Krueger

  I am trying to replicate a subset of Java's DecimalFormat class. Below is what I've come up with. Does this look right to everyone? public class DecimalFormat : NumberFormat { int _maximumFractionDigits; int _minimumFractionDigits; string _format; void RebuildFormat () { _format = "{0:0."; _format += new string ('0', _minimumFractionDigits); if (_maximumFractionDigits > _minimumFractionDigits) { _format += new string ('#', _maximumFractionDigits - _minimumFractionDigits); } _format += "}"; } public override string format (object value) { return string.Format (_format, value); } public override void setMaximumFractionDigits (int n) { _maximumFractionDigits = n; RebuildFormat (); } public override void setMinimumFractionDigits (int n) { _minimumFractionDigits = n; RebuildFormat (); } public override void setGroupingUsed (bool g) { } public static NumberFormat getInstance () { return new DecimalFormat (); } }

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• A textbox class only accept integers in Java

  - by alex

  I just want to do a textbox class onl accepts integers.. I have done something, but i think it's not enough. Can anyone help me, please? Thanks... import java.awt.TextField public class textbox extends TextField{ private int value; public textbox(){ super(); } public textbox(int value){ setDeger(value); } public int getValue() { return value; } public void setValue(int value) { this.value = value; } }

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• java or php tip for small problem

  - by agazerboy

  Hi All, I am having a weird mind gogling problem. Sorry in advance, If I confuse you. I have following data 1 3 5 5 1 2 2 4 8 3 2 9 3 8 4 first column = source 1 second column = source 2 third column = result column First and second column will can create 3rd column and that 3rd column can be used in 1st or 2nd column to make a new 3rd column value. You can see in first row 5 was 3rd column and in 2nd row it was input to make 2 (3rd column) I am looking for a solutin that if it pass 3 it return me (1,4,5) rows and same for other digits. Solution tip can be either in java or php because I just want to get data from a old project to make it work ! Thanks !

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