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  • java - coding errors causing endless loop

    - by Daniel Key
    Im attempting to write a program that takes a population's birthrate and deathrate and loops the annual population until it either reaches 0 or doubles. My problem it that it continuously loops an endless amount of illegible numbers and i cant fix it. please help. //***************************************** //This program displays loop statements //Written by: Daniel Kellogg //Last Edited: 9/28/12 //**************************************** import java.util.Scanner; public class Hwk6 { public static void main (String[] args) { int currentYear, currentPopulation; double birthRate, deathRate; Scanner stdin = new Scanner(System.in); System.out.println("\nPopulation Estimator\n"); System.out.println("Enter Year"); currentYear = stdin.nextInt(); System.out.println("Enter Current Population"); currentPopulation = stdin.nextInt(); System.out.println("Enter Birthrate of Population"); birthRate = stdin.nextDouble(); System.out.println("Enter Deathrate of Population"); deathRate = stdin.nextDouble(); int counter = currentPopulation; System.out.println("Population: "); while (currentPopulation != -1) while (counter < currentPopulation * 2) { System.out.print(counter + " "); counter = counter + (int)(counter * birthRate - counter * deathRate); } System.exit(0); } }

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  • Java map with values limited by key's type parameter

    - by Ashley Mercer
    Is there a way in Java to have a map where the type parameter of a value is tied to the type parameter of a key? What I want to write is something like the following: public class Foo { // This declaration won't compile - what should it be? private static Map<Class<T>, T> defaultValues; // These two methods are just fine public static <T> void setDefaultValue(Class<T> clazz, T value) { defaultValues.put(clazz, value); } public static <T> T getDefaultValue(Class<T> clazz) { return defaultValues.get(clazz); } } That is, I can store any default value against a Class object, provided the value's type matches that of the Class object. I don't see why this shouldn't be allowed since I can ensure when setting/getting values that the types are correct. EDIT: Thanks to cletus for his answer. I don't actually need the type parameters on the map itself since I can ensure consistency in the methods which get/set values, even if it means using some slightly ugly casts.

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  • How to structure applications as multiple projects an name the packages in Java

    - by lostiniceland
    Hello Everyone I would like to know how you set up your projects in Java For example, in my current work-project, a six year old J2EE app with approximately 2 million LoC, we only have one project in Eclipse. The package structure is split into tiers and then domains, so it follows guidelines from Sun/Oracle. A huge ant-script is building different jars out of this one source-folder Personally I think it would be better to have multiple projects, at least for each tier. Recently I was playing around with a projects-structure like this: Domainproject (contains only annotated pojos, needed by all other projects) Datalayer (only persistence) Businesslogic (services) Presenter View This way, it should be easier to exchange components and when using a build tool like Maven I can have everything in a repository so when only working on the frontend I can get the rest as a dependecy in my classpath. Does this makes sense to you? Do you use different approaches and how do they look like? Furthermore I am struggeling how to name my packages/projects correctly. Right now, the above project-structure reflects in the names of the packages, eg. de.myapp.view and it continues with some technical subfolders like internal or interfaces. What I am missing here, and I dont know how to do this properly, is the distinction to a certain domain. When the project gets bigger it would be nice to recognise a particular domain but also the technical details to navigate more easily within the project. This leads to my second question: how do you name your projects and packages?

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  • Java CountDownLatch used to wait for JFrame to dispose

    - by Brian
    I have referenced this previous question as well as other sources, but cannot get CountDownLatch to work correctly. Background: mainFrame creates new Frame called dataEntryFrame. When dataEntryFrame "Submit" button is clicked, record added to database and dataEntryFrame disposed. At this point, mainFrame should clear and reload a jList that shows all records. Issue: When dataEntryFrame loads, java freezes, dataEntryFrame components never load. I cannot get past this part... then, in the DataEntryFrame, CountDownLatch should only decrements after the submit button is clicked, successfully adds a record to a database table, and disposes itself. Or when the user clicks cancel... Code: From MainFrame CountDownLatch dataEntryDone = new CountDownLatch(1); DataEntryFrame f = new DataEntryFrame(dataEntryDone); Thread newThread = new Thread(f); newThread.start(); dataEntryDone.await(); Code: From DataEntryFrame public void run(){ initComponents(); loadOtherData(); this.setVisible(true); } void submit(){ addRecord(); this.dispose() dataEntryDone.countDown(); }

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  • Append data to same text file using java

    - by Manu
    SimpleDateFormat formatter = new SimpleDateFormat("ddMMyyyy_HHmmSS"); String strCurrDate = formatter.format(new java.util.Date()); String strfileNm = "Customer_" + strCurrDate + ".txt"; String strFileGenLoc = strFileLocation + "/" + strfileNm; String Query1="select '0'||to_char(sysdate,'YYYYMMDD')||'123456789' class_code from dual"; String Query2="select '0'||to_char(sysdate,'YYYYMMDD')||'123456789' class_code from dual"; try { Statement stmt = null; ResultSet rs = null; Statement stmt1 = null; ResultSet rs1 = null; stmt = conn.createStatement(); stmt1 = conn.createStatement(); rs = stmt.executeQuery(Query1); rs1 = stmt1.executeQuery(Query2); File f = new File(strFileGenLoc); OutputStream os = (OutputStream)new FileOutputStream(f,true); String encoding = "UTF8"; OutputStreamWriter osw = new OutputStreamWriter(os, encoding); BufferedWriter bw = new BufferedWriter(osw); while (rs.next() ) { bw.write(rs.getString(1)==null? "":rs.getString(1)); bw.write(" "); } bw.flush(); bw.close(); } catch (Exception e) { System.out.println( "Exception occured while getting resultset by the query"); e.printStackTrace(); } finally { try { if (conn != null) { System.out.println("Closing the connection" + conn); conn.close(); } } catch (SQLException e) { System.out.println( "Exception occured while closing the connection"); e.printStackTrace(); } } return objArrayListValue; } The above code is working fine. it writes the content of "rs" resultset data in text file Now what i want is ,i need to append the the content in "rs2" resultset to the "same text file"(ie . i need to append "rs2" content with "rs" content in the same text file)..

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  • Java to C# code converter

    - by acadia
    Hello, Are there any converters available that converts Java code to C#? I need to convert the below code into C# String token = new String(""); URL url1 =new URL( "http", domain, Integer.valueOf(portnum), "/Workplace/setCredentials?op=getUserToken&userId="+username+"&password="+password +"&verify=true"); URLConnection conn1=url1.openConnection(); ((HttpURLConnection)conn1).setRequestMethod("POST"); InputStream contentFileUrlStream = conn1.getInputStream(); BufferedReader br = new BufferedReader(new InputStreamReader(contentFileUrlStream)); token=br.readLine(); String encodedAPIToken = URLEncoder.encode(token); String doubleEncodedAPIToken ="ut=" + encodedAPIToken;//.substring(0, encodedAPIToken.length()-1); //String doubleEncodedAPIToken ="ut=" + URLEncoder.encode(encodedAPIToken); //String userToken = "ut=" + URLEncoder.encode(token, "UTF-8"); //URLEncoder.encode(token); String vsId = "vsId=" + URLEncoder.encode(docId.substring(5, docId.length()), "UTF-8"); url="http://" + domain + ":" + portnum + "/Workplace/getContent?objectStoreName=RMROS&objectType=document&" + vsId + "&" +doubleEncodedAPIToken; String vsId = "vsId=" + URLEncoder.encode(docId.substring(5, docId.length()), "UTF-8"); url="http://" + domain + ":" + portnum + "/Workplace/getContent?objectStoreName=RMROS&objectType=document&" + vsId + "&" +doubleEncodedAPIToken; Thanks in advance

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  • Parsing and replacing Javascript identifiers with Rhino in Java

    - by Parhs
    Suppose I let the user to write a condition using Javascript, the user can write conditions to perform a test and return true or false. E.g.: INS>5 || ASTO.valueBetween(10,210) I want to find which variables are used in the script that the user wrote. I tried to find a way to get the identifier names in Java. The Rhino library didn't help a lot. However I found that via handling exceptions I could get all the identifiers. So this problem is solved. So everything is great, but there is one little problem. How can I replace these identifiers with a numeric identifier? E.g. INS should be _234 and ASTO should be _331. INS and ASTO etc are entities in my database. I want to replace them, because the name may change. I could do it using a replace but this isn't easy because: It should be reversible. E.g. ASTO to _234 and _234 to ASTO again. Replacing _23 with MPLAH may also replace _234. This could be fixed with regexp somehow. What if _23 is in a comment section? Rare to happen, but possible /* _23 fdsafd ktl */. It should also be replaced. What if it is a name of a function? E.g. _32() {}. Also rare, but it shouldn't be replaced. What if it is enclosed in "" or ''? I am sure that there are a lot more cases. Any ideas?

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  • Please recommend a CMS framework in Java good for making a monitoring system

    - by TiansHUo
    I already have Java code to display and process data from a database. I would now like to implement the code as modules, and incorporate as a whole into a CMS system. The CMS MUST support Spring, Hibernate, etc. The CMS MUST not be GPL, and preferably open source (lGPL, BSD,etc). The CMS MUST have good documentation and support The CMS MUST be secure (safe from XSS and injection) and support different levels of authorizations, (built-in or module) The CMS MUST have good navigation and tab, (built-in or module) +1, for having a good ajax paginated table module to display data +1, for using ajax to change pages with support for bookmarks and history.back() +1, for using jquery or prototype +1, for being easy to deploy, and easy to add modules +1, for supporting dynamically add/remove and drag-dropping of modules Please recommend a CMS best for the job. Thank you! EDIT: I don't need blogs or wikis or etc. I just want a framework where I can display paginated lists and time series graphs and log files. I will also host some pages for configuration. All of these code are already implemented.

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  • Playing with bytes...need to convert from java to C#

    - by ibiza
    Hi fellow programmers, I am not used to manipulate bytes in my code and I have this piece of code that is written in Java and I would need to convert it to its C# equivalent : protected static final int putLong(final byte[] b, final int off, final long val) { b[off + 7] = (byte) (val >>> 0); b[off + 6] = (byte) (val >>> 8); b[off + 5] = (byte) (val >>> 16); b[off + 4] = (byte) (val >>> 24); b[off + 3] = (byte) (val >>> 32); b[off + 2] = (byte) (val >>> 40); b[off + 1] = (byte) (val >>> 48); b[off + 0] = (byte) (val >>> 56); return off + 8; } Thanks in advance for all your help, I am looking forward to learn from this.

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  • Variable reference problem when loading an object from a file in Java

    - by Snail
    I have a problem with the reference of a variable when loading a saved serialized object from a data file. All the variables referencing to the same object doesn't seem to update on the change. I've made a code snipped below that illustrates the problem. Tournament test1 = new Tournament(); Tournament test2 = test1; try { FileInputStream fis = new FileInputStream("test.out"); ObjectInputStream in = new ObjectInputStream(fis); test1 = (Tournament) in.readObject(); in.close(); } catch (IOException ex){ Logger.getLogger(Frame.class.getName()).log(Level.SEVERE, null, ex); } catch (ClassNotFoundException ex){ Logger.getLogger(Frame.class.getName()).log(Level.SEVERE, null, ex); } System.out.println("test1: " + test1); System.out.println("test2: " + test2); After this code is ran test1 and test2 doesn't reference to the same object anymore. To my knowledge they should do that since in the declaration of test2 makes it a reference to test1. When test1 is updated test2 should reflect the change and return the new object when called in the code. Am I missing something essential here or have I been misstaught about how the variable references in Java works?

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  • Threads in Java

    - by owca
    I've created simple program to test Threads in Java. I'd like it to print me numbers infinitely, like 123123123123123. Dunno why, but currently it stops after one cycle finishing 213 only. Anyone knows why ? public class Main { int number; public Main(int number){ } public static void main(String[] args) { new Infinite(2).start(); new Infinite(1).start(); new Infinite(3).start(); } } class Infinite extends Thread { static int which=1; static int order=1; int id; int number; Object console = new Object(); public Infinite(int number){ id = which; which++; this.number = number; } @Override public void run(){ while(1==1){ synchronized(console){ if(order == id){ System.out.print(number); order++; if(order >= which){ order = 1; } try{ console.notifyAll(); console.wait(); } catch(Exception e) {} } else { try{ console.notifyAll(); console.wait(); } catch(Exception e) {} } } try{Thread.sleep(0);} catch(Exception e) {} } } }

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  • Java: Clearing up the confusion on what causes a connection reset

    - by Zombies
    There seems to be some confusion as well contradicting statements on various SO answers: http://stackoverflow.com/questions/585599/whats-causing-my-java-net-socketexception-connection-reset . You can see here that the accepted answer states that the connection was closed by other side. But this is not true, closing a connection doesn't cause a connection reset. It is cauesed by "an underlying TCP/IP error." What I want to know is if a SocketException: Connection reset means really besides "unerlying TCP/IP Error." What really causes this? As I doubt it has anything to do with the connection being closed (since closing a connection isn't an exception worthy flag, and reading from a closed connection is, but that isn't an "underlying TCP/IP error." My hypothesis is this Connection reset is caused from a server's failure to acknowledge an ACK packet (either wholly or just improperly as per TCP/IP). And that a SocketTimeoutException is generated only when no data is generated to be read (since this is thrown during a read after a certain duration, and read is waiting for data, but is not concerned with ACK packets). In other words, read() throws SocketTimeoutException if it didn't read any bytes of actual data (DATA LAYER) in its allotted time.

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  • java GC periodically enters into several full GC cycles

    - by Peter
    Environment: sun JDK 1.6.0_16 vm settings: -XX:+DisableExplicitGC -XX:+UseConcMarkSweepGC -Xms1024 -Xmx1024M -XX:MaxNewSize=448m -XX:NewSize=448m -XX:SurvivorRatio=4(6 also checked) -XX:MaxPermSize=128M OS: windows server 2003 processor: 4 cores of INTEL XEON 5130, 2000 Hz my application description: high intensity of concurrent(java 5 concurrency used) operations completed each time by commit to oracle. it's about 20-30 threads run non stop, doing tasks. application runs in JBOSS web container. My GC starts work normally, I see a lot of small GCs and all that time CPU shows good load, like all 4 cores loaded to 40-50%, CPU graph is stable. Then , after 1 min of good work, CPU starts drop to 0% on 2 cores from 4, it's graph becomes unstable, goes up and down("teeth"). I see, that my threads work slower(I have monitoring), I see that GC starts produce a lot of FULL GC during that time and next 4-5 minutes this situation remains as is, then for short period of time, like 1 minute, it gets back to normal situation, but shortly after that all bad thing repeats. Question: Why I have so frequent full GC??? How to prevent that? I played with SurvivorRatio - does not help. I noticed, that application behaves normally until first FULL GC occurs, while I have enough memory. Then it runs badly. my GC LOG: starts good then long period of FULL GCs(many of them) 1027.861: [GC 942200K-623526K(991232K), 0.0887588 secs] 1029.333: [GC 803279K(991232K), 0.0927470 secs] 1030.551: [GC 967485K-625549K(991232K), 0.0823024 secs] 1030.634: [GC 625957K(991232K), 0.0763656 secs] 1033.126: [GC 969613K-632963K(991232K), 0.0850611 secs] 1033.281: [GC 649899K(991232K), 0.0378358 secs] 1035.910: [GC 813948K(991232K), 0.3540375 secs] 1037.994: [GC 967729K-637198K(991232K), 0.0826042 secs] 1038.435: [GC 710309K(991232K), 0.1370703 secs] 1039.665: [GC 980494K-972462K(991232K), 0.6398589 secs] 1040.306: [Full GC 972462K-619643K(991232K), 3.7780597 secs] 1044.093: [GC 620103K(991232K), 0.0695221 secs] 1047.870: [Full GC 991231K-626514K(991232K), 3.8732457 secs] 1053.739: [GC 942140K(991232K), 0.5410483 secs] 1056.343: [Full GC 991232K-634157K(991232K), 3.9071443 secs] 1061.257: [GC 786274K(991232K), 0.3106603 secs] 1065.229: [Full GC 991232K-641617K(991232K), 3.9565638 secs] 1071.192: [GC 945999K(991232K), 0.5401515 secs] 1073.793: [Full GC 991231K-648045K(991232K), 3.9627814 secs] 1079.754: [GC 936641K(991232K), 0.5321197 secs]

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  • XML/RDF to Java Objects with XSD

    - by bmucklow
    So here's the scenario...I have an XSD file describing all the objects that I need. I can create the objects in Java using JAXB no problem. I have an XML/RDF file that I need to parse into those objects. What is the EASIEST way to do this? I have been looking into Jena and have played around with it, but can't see how to easily map the XML/RDF file to the XSD objects that were generated. Here is a snippet of the XSD file as well as the XML/RDF file: <?xml version="1.0" encoding="UTF-8"?> <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:a="http://langdale.com.au/2005/Message#" xmlns:sawsdl="http://www.w3.org/ns/sawsdl" targetNamespace="http://iec.ch/TC57/2007/profile#" elementFormDefault="qualified" attributeFormDefault="unqualified" xmlns="http://langdale.com.au/2005/Message#" xmlns:m="http://iec.ch/TC57/2007/profile#"> <xs:annotation/> <xs:element name="Profile" type="m:Profile"/> <xs:complexType name="Profile"> <xs:sequence> <xs:element name="Breaker" type="m:Breaker" minOccurs="0" maxOccurs="unbounded"/> And the XML/RDF: <!-- CIM XML Output For switch783:(295854688) --> <cim:Switch rdf:ID="Switch_295854688"> <cim:IdentifiedObject.mRID>Switch_295854688</cim:IdentifiedObject.mRID> <cim:IdentifiedObject.aliasName>Switch_295854688</cim:IdentifiedObject.aliasName> <cim:ConductingEquipment.phases rdf:resource="http://iec.ch/TC57/2009/CIM-schema-cim14#PhaseCode.ABC" /> <cim:Switch.circuit2>0001406</cim:Switch.circuit2> <cim:Equipment.Line rdf:resource="#Line_0001406" />

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  • Persistant Http client connections in java

    - by Akusete
    I am trying to write a simple Http client application in Java and am a bit confused by the seemingly different ways to establish Http client connections, and efficiently re-use the objects. Current I am using the following steps (I have left out exception handling for simplicity) Iterator<URI> uriIterator = someURIs(); HttpClient client = new DefaultHttpClient(); while (uriIterator.hasNext()) { URI uri = uriIterator.next(); HttpGet request = new HttpGet(uri); HttpResponse response = client.execute(request); HttpEntity entity = response.getEntity(); InputStream s = entity.getContent(); processStream (); s.close(); } In regard to the code above, my questions is: Assuming all URI's are pointing to the same host (but different resources on that host). What is the recommended way to use a single http connection for all requests? And how do you close the connection after the last request? --edit: Also what is the difference between using uri.openConnection(), versus HttpClient? Which is preferable, and what other methods exist?

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  • exception in thread "main" java.lang.NoclassDefFoundError: cal/class

    - by Gaurav
    enter import java.io.*; class eval { double add(double a,double b) { return (a+b); } double sub(double a,double b) { return (a-b); } double mul(double a,double b) { return (a*b); } double div(double a,double b) { return (a/b); } } class cal extends eval { public static void main(String args[])throws IOException { eval a1=new eval(); try{ System.out.println("1) Add"); System.out.println("2) Subtract"); System.out.println("3) Multiply"); System.out.println("4) Divide"); System.out.println("5) Enter your choice"); BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); int ch;ch=Integer.parseInt(br.readLine()); System.out.println("Enter two number"); double a;a=Integer.parseInt(br.readLine()); double b;b=Integer.parseInt(br.readLine()); switch(ch) { case 1: a1.add(a,b); break; case 2: a1.sub(a,b); break; case 3: a1.mul(a,b); break; case 4: a1.div(a,b); break; } } catch (IOException e) { System.out.println("Error occured, please restart application."); } } }

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  • Help with Hashmaps in Java

    - by Crystal
    I'm not sure how I use get() to get my information. Looking at my book, they pass the key to get(). I thought that get() returns the object associated with that key looking at the documentation. But I must be doing something wrong here.... Any thoughts? import java.util.*; public class OrganizeThis { /** Add a person to the organizer @param p A person object */ public void add(Person p) { staff.put(p, p.getEmail()); System.out.println("Person " + p + "added"); } /** * Find the person stored in the organizer with the email address. * Note, each person will have a unique email address. * * @param email The person email address you are looking for. * */ public Person findByEmail(String email) { Person aPerson = staff.get(email); return aPerson; } private Map<Person, String> staff = new HashMap<Person, String>(); public static void main(String[] args) { OrganizeThis testObj = new OrganizeThis(); Person person1 = new Person("J", "W", "111-222-3333", "[email protected]"); testObj.add(person1); System.out.println(testObj.findByEmail("[email protected]")); } }

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  • Java Concurrency in practice sample question

    - by andy boot
    I am reading "Java Concurrency in practice" and looking at the example code on page 51. According to the book this piece of code is at risk of of failure if it has not been published properly. Because I like to code examples and break them to prove how they work. I have tried to make it throw an AssertionError but have failed. (Leading me to my previous question) Can anyone post sample code so that an AssertionError is thrown? Rule: Do not modify the Holder class. public class Holder{ private int n; public Holder(int n){ this.n = n; } public void assertSanity(){ if (n != n) { throw new AssertionError("This statement is false"); } } } I have modified the class to make it more fragile but I still can not get an AssertionError thrown. class Holder2{ private int n; private int n2; public Holder2(int n) throws InterruptedException{ this.n = n; Thread.sleep(200); this.n2 = n; } public void assertSanity(){ if (n != n2) { throw new AssertionError("This statement is false"); } } } Is it possible to make either of the above classes throw an AssertionError? Or do we have to accept that they may occasionally do so and we can't write code to prove it?

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  • Reversing permutation of an array in Java efficiently

    - by HansDampf
    Okay, here is my problem: Im implementing an algorithm in Java and part of it will be following: The Question is to how to do what I will explain now in an efficient way. given: array a of length n integer array perm, which is a permutation of [1..n] now I want to shuffle the array a, using the order determined by array perm, i.e. a=[a,b,c,d], perm=[2,3,4,1] ------ shuffledA[b,c,d,a], I figured out I can do that by iterating over the array with: shuffledA[i]=a[perm[i-1]], (-1 because the permutation indexes in perm start with 1 not 0) Now I want to do some operations on shuffledA... And now I want to do the reverse the shuffle operation. This is where I am not sure how to do it. Note that a can hold an item more than once, i.e. a=[a,a,a,a] If that was not the case, I could iterate perm, and find the corresponding indexes to the values. Now I thought that using a Hashmap instead of the the perm array will help. But I am not sure if this is the best way to do.

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  • Java - Problem in deploying Web Application

    - by Yatendra Goel
    I have built a Java Web Application and packed it in a .war file and tested it on my local tomcat server and it is running fine. But when I deployed it on my client's server, it is showing an error. According to the remote server (my client's server), it is not finding a tld file packed in a jar file which I had placed in WEB-INF/lib directory. But when I checked the WEB-INF/lib directory for the jar file, i found that it was there. The contents of META-INF/MANIFEST.MF is as follows: Manifest-Version: 1.0 Class-Path: I think that there is no need to explicitly mention the classpath of WEB-INF/lib directory as it is in the classpath of any web application by default. Then, why the server can't find the jar file in the lib directory when I deployed it on a remote server and why it is working when I deployed the same application on my local server. I posted a question for this at http://stackoverflow.com/questions/2441254/struts-1-struts-taglib-jar-is-not-being-found-by-my-web-application but found that the problem is unusual as nobody could answer it. So my questions are as follows: Q1. Is WEB-INF/lib still remains on the classpath if I leave the classpath entry blank as shown above in the MANIFEST.MF file or I should delete the classpath entry completely from the file or I should explicitly enter Class-Path: /WEB-INF/lib as the classpath entry? Q2. I have JSP pages, Servlets and some helper classes in the web application. Jsp pages are located at the root. Servlets and helper classes are located in WEB-INF/classes folder. So Is there any problem if my helper classes are located in the WEB-INF/classes folder? Note: Please note that this question is not same as my previous question. It is a follow-up question of my previous question. Both the servers (local and remote) are tomcat servers.

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  • Java semaphore to syncronize printing to screen

    - by Travis Griswald
    I'm currently stuck on a bit of homework and was wondering if anyone could help - I have to use semaphores in java to syncronize printing letters from 2 threads - one printing "A" and one printing "B". I cannot print out more than 2 of the same character in a row, so output should look like AABABABABABBABABABABAABBAABBABABA At the moment I have 3 semaphores, a binary mutex set to 1, and a counting semaphore, and my thread classes look something like this - public void run() { while (true) { Time.delay(RandomGenerator.integer(0,20)); Semaphores.mutex.down (); System.out.println (produce()); if (printCount > 1) { printCount = 0; Semaphores.mutex.up (); Semaphores.printB.up(); } } } public String produce() { printCount++; return "A"; } public void run() { while (true) { Time.delay(RandomGenerator.integer(0,20)); Semaphores.mutex.down (); System.out.println (produce()); if (printCount > 1) { printCount = 0; Semaphores.mutex.up (); Semaphores.printA.up(); } } } public String produce() { printCount++; return "B"; } Yet whatever I try it either deadlocks, or it seems to be working only printing 2 in a row at most, but always seems to print 3 in a row every now and again! Any help is much appreciated, not looking code or anything just a few pointers if possible :)

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  • Question about cloning in Java

    - by devoured elysium
    In Effective Java, the author states that: If a class implements Cloneable, Object's clone method returns a field-by-field copy of the object; otherwise it throws CloneNotSupportedException. What I'd like to know is what he means with field-by-field copy. Does it mean that if the class has X bytes in memory, it will just copy that piece of memory? If yes, then can I assume all value types of the original class will be copied to the new object? class Point { private int x; private int y; @Override public Point clone() { return (Point)super.clone(); } } If what Object.clone() does is a field by field copy of the Point class, I'd say that I wouldn't need to explicitly copy fields x and y, being that the code shown above will be more than enough to make a clone of the Point class. That is, the following bit of code is redundant: @Override public Point clone() { Point newObj = (Point)super.clone(); newObj.x = this.x; //redundant newObj.y = this.y; //redundant } Am I right? I know references of the cloned object will point automatically to where the original object's references pointed to, I'm just not sure what happens specifically with value types. If anyone could state clearly what Object.clone()'s algorithm specification is (in easy language) that'd be great. Thanks

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  • Translation of a RoR view to Java

    - by mnml
    Hi, for some reasons I am trying to translate the following RoR view code to a GSP view: List<Object> objectscontains the data I want to display in 3 columns <% modulo_objects = @objects.length % 3 base = @objects.length / 3 base = base.ceil case modulo_objects when 0 cols = [base, base, base] when 1 cols = [base, base + 1, base] when 2 cols = [base + 1, base, base + 1] end counter = 0 %> <% 3.times do |i| %> <td width="220" align="center" style="padding-right: 15px;"> <% cols[i].times do %> <h1><a href="/objects/show/<%= @objects[counter].urlname %>" ><%= @objects[counter].name %></a></h1> <% counter = counter + 1 %> <% end %> </td> <% end %> This is what I got so far: #{extends 'main.html' /} %{ modulo_objects = objects.size() % 3 base = objects.size() / 3 base = Math.ceil(base) if(modulo_objects == 0) cols = [base, base, base] else if(modulo_objects == 1) cols = [base, base + 1, base] else if(modulo_objects == 2) cols = [base + 1, base, base + 1] endif counter = 0 }% #{list items:1..3, as:'i'} <td width="220" align="center" style="padding-right: 15px;"> #{list items:cols[i]} <a href="@{Objects.show(objects.get(counter).name.replaceAll(" ", "-"))}" >${objects.get(counter).name}</a> %{ counter = counter + 1 }% #{/list} </td> #{/list} The idea is to keep the items organised in 3 columns like 1|0|1 4|5|4 or 5|4|5 for example, I don't really understand if #{list items:cols[i]} will reproduce ruby's cols[i].times do. So far the Java view is does not display more than two elements.

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  • Java inheritance and super() isn't working as expected

    - by dwwilson66
    For a homework assignment, I'm working with the following. It's an assigned class structure, I know it's not the best design by a long shot. Class | Extends | Variables -------------------------------------------------------- Person | None | firstName, lastName, streetAddress, zipCode, phone CollegeEmployee | Person | ssn, salary,deptName Faculty | CollegeEmployee | tenure(boolean) Student | person | GPA,major So in the Faculty class... public class Faculty extends CollegeEmployee { protected String booleanFlag; protected boolean tenured; public Faculty(String firstName, String lastName, String streetAddress, String zipCode, String phoneNumber,String ssn, String department,double salary) { super(firstName,lastName,streetAddress,zipCode,phoneNumber, ssn,department,salary); String booleanFlag = JOptionPane.showInputDialog (null, "Tenured (Y/N)?"); if(booleanFlag.equals("Y")) tenured = true; else tenured = false; } } It was my understanding that super() in Faculty would allow access to the variables in CollegeEmployee as well as Person. With the code above, it compiles fine when I ONLY include the Person variables. As soon as I try to use ssn, department, or salary I get the following compile errors. Faculty.java:15: error: constructor CollegeEmployee in class CollegeEmployee can not be applied to the given types: super(firstName,lastName,streetAddress,zipCode,phoneNumber,ssn,department,salary); ^ Required: String,String,String,String,String Found: String,String,String,String,String,String,String,String reason: actual and formal argument lists differ in length I'm completely confused by this error...which is the actual and formal? Person has five arguments, CollegeEmployee has 3, so my guess is that something's funky with how the parameters are being passed...but I'm not quite sure where to begin fixing it. What am I missing?

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  • Skipping the BufferedReader readLine() method in java

    - by DDP
    Is there a easy way to skip the readLine() method in java if it takes longer than, say, 2 seconds? Here's the context in which I'm asking this question: public void run() { boolean looping = true; while(looping) { for(int x = 0; x<clientList.size(); x++) { try { Comm s = clientList.get(x); String str = s.recieve(); // code that does something based on the string in the line above } // other stuff like catch methods } } } Comm is a class I wrote, and the receive method, which contains a BufferedReader called "in", is this: public String recieve() { try { if(active) return in.readLine(); } catch(Exception e) { System.out.println("Comm Error 2: "+e); } return ""; } I've noticed that the program stops and waits for the input stream to have something to read before continuing. Which is bad, because I need the program to keep looping (as it loops, it goes to all the other clients and asks for input). Is there a way to skip the readLine() process if there's nothing to read? I'm also pretty sure that I'm not explaining this well, so please ask me questions if I'm being confusing.

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