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  • Writing to an already existing file using FileWriter Java

    - by delo
    Is there anyway I can write to an already existing file using Filewriter For example when the user clicks a submit button: FileWriter writer = new FileWriter("myfile.csv"); writer.append("LastName"); writer.append(','); writer.append("FirstName"); writer.append('/n'); writer.append(LastNameTextField.getText()); writer.append(','); writer.append(FirstNameTextField.getText()); I want to be able to write new data into the already existing myfile.csv without having to recreate a brand new one every time

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  • "Dynamic" java validation framework?

    - by pihentagy
    AFAIK JSR-303 is the standard bean validation system. I don't know whether it could do validations like this (I guess no): if an object has a deleted flag set, you cannot modify the object you cannot change the start date property, after the date is passed you cannot decrease some integer properties in the bean So how can I handle validations, which depend on the previous state of an object? I would like to solve problems like that in hibernate3.5 - spring3 - JPA2 environment. Thanks My solution was to mess with hibernate, reload the object to see the old state (after evicting the new object). This time I need some smarter solution...

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  • Shallow Copy in Java

    - by Vilius
    Hello there! I already know, what a shallow copy is, but I'm not able to impliment it. Here's a short example. public class Shallow { String name; int number; public Shallow (String name, int number) { this.name = name; this.number = number; } } Test the implementation ... public class ShallowTest { public static void main (String[] args) { Shallow shallow = new Shallow("Shallow", 123); Shallow shallowClone = new Shallow(shallow); shallowClone.name = 'Peter'; shallowClone.number = 321; System.out.println(shallow.name + " - " + shallow.number); } } As I purpose, just the reference of the non primitive datatype String would be copied, so that by calling "shallowClone.name = 'Peter';" I would also change the name of "shallow". Am I right? But somehow, it just does not want to work ....

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  • java concurrency assignments

    - by dev
    I am JEE developer, and I want to get skills on concurrency development. Could you provide me some assignments, ideas, or other - just for learning and training concurrency programming? Thanks!

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  • How to solve following issue in java?

    - by lakshmi
    Im getting following error while running the query. org.hibernate.hql.ast.QuerySyntaxException: expecting CLOSE, found 'LIMIT' near line 1, column 194 [from com.claystone.db.Gpsdata where id.mobileunitid = '2090818044' and gpsdate in (select id.gpsdate from com.claystone.db.Gpsdata where id.mobileunitid = '2090818044' ORDER BY id.gpsdate DESC LIMIT 1 ) and gpsstatus='true'] This is my Query.Please give the suggession what is the mistake in this query? data=session.createQuery[from com.claystone.db.Gpsdata where id.mobileunitid = '2090818044' and gpsdate in (select id.gpsdate from com.claystone.db.Gpsdata where id.mobileunitid = '2090818044' ORDER BY id.gpsdate DESC LIMIT 1 ) and gpsstatus='true']

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  • Java Enum List from Class

    - by DD
    How do I go from a Class object to a list of enums generically? i.e. public static <T extends Enum> List<T> getList(Class<T> clazz) I cant find a way to get to the values() method

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  • using regular expression in Java

    - by Mrityunjay
    Hi, i need to check a string that should contain only ABCDEFG characters, in any sequence and with only 7 characters. Please let me know the correct way of using regular expression. as corrently i am using String abs = "ABPID"; if(!Pattern.matches("[[ABCDEFG]", abs)) System.out.println("Error"); i am using the following code which works when i use the String abcdefg but for other cases it fails. please help me out.

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  • Implement dictionary using java

    - by ahmad
    Task Dictionary ADT The dictionary ADT models a searchable collection of key-element entries Multiple items with the same key are allowed Applications: word-definition pairs Dictionary ADT methods: find(k): if the dictionary has an entry with key k, returns it, else, returns null findAll(k): returns an iterator of all entries with key k insert(k, o): inserts and returns the entry (k, o) remove(e): remove the entry e from the dictionary size(), isEmpty() Operation Output Dictionary insert(5,A) (5,A) (5,A) insert(7,B) (7,B) (5,A),(7,B) insert(2,C) (2,C) (5,A),(7,B),(2,C) insert(8,D) (8,D) (5,A),(7,B),(2,C),(8,D) insert(2,E) (2,E) (5,A),(7,B),(2,C),(8,D),(2,E) find(7) (7,B) (5,A),(7,B),(2,C),(8,D),(2,E) find(4) null (5,A),(7,B),(2,C),(8,D),(2,E) find(2) (2,C) (5,A),(7,B),(2,C),(8,D),(2,E) findAll(2) (2,C),(2,E) (5,A),(7,B),(2,C),(8,D),(2,E) size() 5 (5,A),(7,B),(2,C),(8,D),(2,E) remove(find(5)) (5,A) (7,B),(2,C),(8,D),(2,E) find(5) null (7,B),(2,C),(8,D),(2,E) Detailed explanation: NO Specific requirements: please Get it done i need HELP !!!

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  • Scaling Java applications - existing cluster-aware IoC frameworks?

    - by Zoltan
    Most people use some kind of an IoC framework - Guice, Spring, you name it. Many of us need to scale their applications too, so they complicate their lifes with Terracotta, Glassfish/JBoss/insertyourfavouritehere clusters. But is it really the way to go? Are you using any of the above? Here's some ideas we currently have implemented in a yet-to-be-opensourced framework, and I'd like to see what you think of it, or maybe "it's a complete ripoff of XY!". cluster-wide object replication - give it a name, and whenever you do something (in any node) on such an object, it will get replicated - with different guarantees do transparent soft-loadbalancing - simplest scenario: restful webservice method call proxied to an other node view-only node injection: inject a proxy to a "named" object, and get your calls automatically proxied to a node Would you use something like that? Is there a current, stable, enterprise-ready implementation out there?

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  • Insert code into a method - Java

    - by DutrowLLC
    Is there a way to automatically insert code into a method? I have the following and I would like to insert the indicated code: public class Person { Set<String> updatedFields = new LinkedHashSet<String>(); String firstName; public String getFirstName(){ return firstName; } boolean isFirstNameChanged = false; // Insert public void setFirstName(String firstName){ if( !isFirstNameChanged ){ // Insert isFirstNameChanged = true; // Insert updatedFields.add("firstName"); // Insert } // Insert this.firstName = firstName; } } I'm also not sure if I can the subset of the method name as a string from inside the method itself as indicated on the line where I add the fieldName as a string into the set of updated fields: updatedFields.add("firstName");. And I'm not sure how to insert fields into a class where I add the boolean field that tracks if the field has been modified or not before (for efficiency to prevent having to manipulate the Set): boolean isFirstNameChanged = false; It seems to most obvious answer to this would be to use code templates inside eclipse, but I'm concerned about having to go back and change the code later.

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  • copy file from one location to another location in linux using java program

    - by Mouli
    Using JSP am trying to move customer logo into another location in linux but its not working. thanks in advance Here is my program String customerLogo = request.getParameter("uploadCustomerLogo").trim(); StringBuffer absoluteFolderPath = new StringBuffer(); absoluteFolderPath.append("/zoniac"); absoluteFolderPath.append("/Companies/"); absoluteFolderPath.append("companyCode/"); absoluteFolderPath.append("custom/"); String destination = absoluteFolderPath.toString(); File sourcefile = new File(customerLogo); File destfile = new File(destination+sourcefile.getName()); FileUtils.copyFile(sourcefile,destfile);

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  • Java: getInputMap(WHEN_IN_FOCUSED_WINDOW) from within JInternalFrame

    - by gerardlouw
    I have a component inside a JInternalFrame which needs to perform actions when keys are pressed within the JInternalFrame's parenting window. Using InputMap/ActionMap would be ideal, but the getInputMap(WHEN_IN_FOCUSED_WINDOW) of the component returns an InputMap that treats the JInternalFrame as the "focused window", rather than its parenting window. Any solutions or ideas?

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  • Timeout with GAE Java

    - by user242153
    Hi, I am having some issues with an app I have deployed on GAE. Specifically, I am intermittently running into the DeadlineExceededException where the server is not responding within the 30 seconds required. What is odd is that the code is not overly complex, it should run in milliseconds. My guess is that the delay is in dealing with the persistence manager and accessing the datastore. 2 questions: 1) What is the best way to track where all of the CPU time on the server is being used up? Log files do not seem helpful and to make things more complicated the code runs very fast when I am running it locally 2) Any tips / best practices in dealing with the 30 second exception? What are the biggest drivers of this? Datastore? HTTP requests / responses? Thanks

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  • Building a control-flow graph from an AST with a visitor pattern using Java

    - by omegatai
    Hi guys, I'm trying to figure out how to implement my LEParserCfgVisitor class as to build a control-flow graph from an Abstract-Syntax-Tree already generated with JavaCC. I know there are tools that already exist, but I'm trying to do it in preparation for my Compilers final. I know I need to have a data structure that keeps the graph in memory, and I want to be able to keep attributes like IN, OUT, GEN, KILL in each node as to be able to do a control-flow analysis later on. My main problem is that I haven't figured out how to connect the different blocks together, as to have the right edge between each blocks depending on their nature: branch, loops, etc. In other words, I haven't found an explicit algorithm that could help me build my visitor. Here is my empty Visitor. You can see it works on basic langage expressions, like if, while and basic operations (+,-,x,^,...) public class LEParserCfgVisitor implements LEParserVisitor { public Object visit(SimpleNode node, Object data) { return data; } public Object visit(ASTProgram node, Object data) { data = node.childrenAccept(this, data); return data; } public Object visit(ASTBlock node, Object data) { } public Object visit(ASTStmt node, Object data) { } public Object visit(ASTAssignStmt node, Object data) { } public Object visit(ASTIOStmt node, Object data) { } public Object visit(ASTIfStmt node, Object data) { } public Object visit(ASTWhileStmt node, Object data) { } public Object visit(ASTExpr node, Object data) { } public Object visit(ASTAddExpr node, Object data) { } public Object visit(ASTFactExpr node, Object data) { } public Object visit(ASTMultExpr node, Object data) { } public Object visit(ASTPowerExpr node, Object data) { } public Object visit(ASTUnaryExpr node, Object data) { } public Object visit(ASTBasicExpr node, Object data) { } public Object visit(ASTFctExpr node, Object data) { } public Object visit(ASTRealValue node, Object data) { } public Object visit(ASTIntValue node, Object data) { } public Object visit(ASTIdentifier node, Object data) { } } Can anyone give me a hand? Thanks!

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  • Java Runtime.freeMemory() returning bizarre results when adding more objects

    - by Sotirios Delimanolis
    For whatever reason, I wanted to see how many objects I could create and populate a LinkedList with. I used Runtime.getRuntime().freeMemory() to get the approximation of free memory in my JVM. I wrote this: public static void main(String[] arg) { Scanner kb = new Scanner(System.in); List<Long> mem = new LinkedList<Long>(); while (true) { System.out.println("Max memory: " + Runtime.getRuntime().maxMemory() + ". Available memory: " + Runtime.getRuntime().freeMemory() + " bytes. Press enter to use more."); String s = kb.nextLine(); if (s.equals("m")) for (int i = 0; i < 1000000; i++) { mem.add(new Long((new Random()).nextLong())); } } } If I write in m, the app adds a million Long objects to the list. You would think the more objects (to which we have references, so can't be gc'ed), the less free memory. Running the code: Max memory: 1897725952. Available memory: 127257696 bytes. m Max memory: 1897725952. Available memory: 108426520 bytes. m Max memory: 1897725952. Available memory: 139873296 bytes. m Max memory: 1897725952. Available memory: 210632232 bytes. m Max memory: 1897725952. Available memory: 137268792 bytes. m Max memory: 1897725952. Available memory: 239504784 bytes. m Max memory: 1897725952. Available memory: 169507792 bytes. m Max memory: 1897725952. Available memory: 259686128 bytes. m Max memory: 1897725952. Available memory: 189293488 bytes. m Max memory: 1897725952. Available memory: 387686544 bytes. The available memory fluctuates. How does this happen? Is the GC cleaning up other things (what other things are there on the heap to really clean up?), is the freeMemory() method returning an approximation that's way off? Am I missing something or am I crazy?

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  • create a sparse BufferedImage in java

    - by elgcom
    I have to create an image with very large resolution, but the image is relatively "sparse", only some areas in the image need to draw. For example with following code /* this take 5GB memory */ final BufferedImage img = new BufferedImage( 36000, 36000, BufferedImage.TYPE_INT_ARGB); /* draw something */ Graphics g = img.getGraphics(); g.drawImage(....); /* output as PNG */ final File out = new File("out.png"); ImageIO.write(img, "png", out); The PNG image on the end I created is ONLY about 200~300 MB. The question is how can I avoid creating a 5GB BufferedImage at the beginning? I do need an image with large dimension, but with very sparse color information. Is there any Stream for BufferedImage so that it will not take so much memory?

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  • Best approach to create a security environment in Java

    - by Tom Brito
    I need to create a desktop application that will run third party code, and I need to avoid the third party code from export by any way (web, clipboard, file io) informations from the application. Somethig like: public class MyClass { private String protectedData; public void doThirdPartyTask() { String unprotedtedData = unprotect(protectedData); ThirdPartyClass.doTask(unprotectedData); } private String unprotect(String data) { // ... } } class ThirdPartyClass { public static void doTask(String unprotectedData) { // Do task using unprotected data. // Malicious code may try to externalize the data. } } I'm reading about SecurityManager and AccessControler, but I'm still not sure what's the best approach to handle this. What should I read about to do this implementation?

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