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• GA written in Java

  - by EnderMB

  I am attempting to write a Genetic Algorithm based on techniques I had picked up from the book "AI Techniques for Game Programmers" that uses a binary encoding and fitness proportionate selection (also known as roulette wheel selection) on the genes of the population that are randomly generated within the program in a two-dimensional array. I recently came across a piece of pseudocode and have tried to implement it, but have come across some problems with the specifics of what I need to be doing. I've checked a number of books and some open-source code and am still struggling to progress. I understand that I have to get the sum of the total fitness of the population, pick a random number between the sum and zero, then if the number is greater than the parents to overwrite it, but I am struggling with the implementation of these ideas. Any help in the implementation of these ideas would be very much appreciated as my Java is rusty.

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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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• 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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• 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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• How to get surrounding method in Java source file for a given line number

  - by roesslerj

  I have a line number of a Java source file and want to get the sourounding method for that line number programatically. I looked into ANTLR which didn't help me much. Janino (http://www.janino.net) seems promising, I would scan and parse (and if necessary compile) the code. Then I could use JDI and ReferenceType.locationsOfLine(int lineNumber) Still I don't know how to use JDI for doing this and didn't find a tutorial that goes anywhere in this direction. Maybe there is some other way that I am completely missing.

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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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• 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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• 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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• How to read an XML file with Java?

  - by Yatendra Goel

  I don't need to read complex XML files. I just want to read the following configuration file with a simplest XML reader <config> <db-host>localhost</db-host> <db-port>3306</db-port> <db-username>root</db-username> <db-password>root</db-password> <db-name>cash</db-name> </config> How to read the above XML file with a XML reader through Java?

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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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• Java array assignment (multiple values)

  - by Danny King

  Hello, I have a Java array defined already e.g. float[] values = new float[3]; I would like to do something like this further on in the code: values = {0.1f, 0.2f, 0.3f}; But that gives me a compile error. Is there a nicer way to define multiple values at once, rather than doing this?: values[0] = 0.1f; values[1] = 0.2f; values[2] = 0.3f; Thanks!

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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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• Inheritance in Java

  - by stevebot

  If I have an abstract class in java named Foo and it has an implementor named Bar then I want to know the following. lets say Foo looks something like public abstract class Foo { Service serviceFoo ... } And Bar is public class Bar extends Foo { ... } Also, lets assume I have an instance with Foo, named foo, currently that has serviceFoo instantiated If I then declare: Foo foo = new Bar(); will this create a a new instance of Bar that has serviceFoo instantiated or not? E.g. will that field be inherited and instantiated or just inherited?

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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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• What is the best Java numerical method package?

  - by Bob Cross

  I am looking for a Java-based numerical method package that provides functionality including: Solving systems of equations using different numerical analysis algorithms. Matrix methods (e.g., inversion). Spline approximations. Probability distributions and statistical methods. In this case, "best" is defined as a package with a mature and usable API, solid performance and numerical accuracy. Edit: derick van brought up a good point in that cost is a factor. I am heavily biased in favor of free packages but others may have a different emphasis.

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• Mapping java.util.Date to xs:date instead of xs:dateTime in JAX-WS

  - by Larsing

  Hi all, We hav an EJB, jws-anotated as a web service. It has a pretty complex pojo-model that generates an equally complex xsd. The pojos contain numerous java.util.Date. These all map to xs:dateTime. This service is used as "business service" in Oracle(BEA) OSB(AquaLogic). We also have a "proxy service" which we map to the BS with XQuery (the OSB/AquaLogic way). The proxy service's xsd has xs:date for the corresponding fields. For some reason, Oracle's implementation of XQuery does not support casting from xs:date to xs:dateTime(!). I could solve this by casting to xs:string and concat:ing with "T00:00:00", however, i would rather try to get JAX-WS to generate an xsd with xs:date instead. Only, I can't find any info on how to do this (anotations?). Can anyone give me a hint? Kind regards, Lars

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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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• How to generate a random alpha-numeric string in Java

  - by Todd

  I've been looking for a simple java algorithm to generate a pseudo-random alpha-numeric string. In my situation it would be used as a unique session/key identifier that would "likely" be unique over 500K+ generation (my needs don't really require anything much more sophisticated) . Ideally I would be able to specify a length depending on my uniqueness needs. For example, a generated string of length 12 might look something like "AEYGF7K0DM1X". Answers: I like @Apocalisp and @erickson's answers equally well. The only downside to @Apocalisp's answer is it requires an apache class. Thanks to both for the help!

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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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• 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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• 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 Non-Blocking HTTP Server

  - by Marcus

  I have written an application using embedded Jetty that makes network calls to other services. I presume that the serving threads are idle whilst waiting for the network calls to complete. Is there any way to have a worker thread that switches between requests to perform work that can be done at the current time and then when the network calls return also handle that? A request would be returned when all work has been completed for it. I know this is a common paradigm, and I have used it for non-blocking TCP networking, but I'm unsure as to how to achieve this on a Java HTTP server whilst also waiting on external results. Any links or explanations are appreciated. Thanks

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• Separation of static and dynamic content in Java EE applications

  - by Dan

  We work with IBM products and we typically use IBM Http Servers (read Apache) as a reverse proxy for our application servers. For performance reasons we serve static content (.gif, .jpg, .css, .html etc.) from our http servers, to ease the burden a bit from the application server. So far, we have to distribute files to http server and configure it manually (writing custom scripts at best.) The problem is the effort needed to keep everything in synch, especially when you need to update the app. Does any Java EE product support this “out of the box”? Is there a way to have application server do this automatically, like in cluster configuration for example, where master node is in charge of distributing the application to other nodes and for keeping everything in synch.

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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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