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  • High performance distributed asynchronous RPC in java

    - by unludo
    I would like to do RPC to a list of clients with the following requirements: the server does not know the clients (implies a kind of broker?) and the cleints do not know the server there may be several clients - they share the load to treat the RPC The RPC is asynchronous very fast (round-trip < 1ms) optional : offers a fail-over mechanism. It can be done with underlying tools which are not really intended for that (Hazelcast is an example). What would you use for such requirements? Thanks!

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  • How to load modules in Java

    - by gerardorn
    I'm building a server that loads modules. Each module is a .jar file. Inside the jar there's all the classes that the module needs. The server needs to read the jar, find the main class (it doesnt have the main method on it is just the class that makes the module work but not as a different program), build an object of that class and store it in a vector of modules so that it can acces to a specific module depending on the job to be done. How can I do that? As far as the server, it is listening and receiving request, but there's no modules to delegate the job to, since my vector of modules is empty.

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  • Java: limit to nest classes?

    - by HH
    A very poor style to code but sometimes unavoidable. It is an extreme example. So is there some limit for nesting classes? are they equivalent? how do you deal with such situations? Create library? Code new FileObject().new Format().new Words().new Some().new Continue someThing; ((((new FileObject()).new Format()).new Words()).new Some()).new Continue someThing;

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  • Thread Code...anything wrong with this, must use java 1.4

    - by bmw0128
    I have a servlet automatically firing up when the app server starts, and in its init(), I'm making another thread: init(){ new FooThread() } in FooThread(), i want to periodically check the status of a DB value, then depending on the value, make a web service call. When these two tasks complete, I want the thread to sleep to wait a certain period then repeat. This cycle would just continue forever. FooThread: public class FooThread implements Runnable{ Thread t; FooThread(){ t = new Thread(this, "BBSThread"); logger.info("*** about to start " + t.getName()); t.start(); logger.info("*** started: " + t); } public void run() { try{ while(true){ //do the db check, then conditionally do the web services call logger.info("*** calling sleep() ***"); Thread.sleep(50000); logger.info("*** now awake ***"); } } catch (InterruptedException e) { System.out.println("*** FooThread interrupted"); } } }

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  • Relational Database arrays (H2, Java)

    - by Daddy Warbox
    I seem to have two options on how to implement arrays, and I want to know which I should go with: Use the ARRAY data type and (from what I understand) effectively serialize data objects into the database (which in my case are just wrapped primitive types; don't know of another way to make this work). Use a separate table and map with foreign keys for each array item. If you have experience with this (especially with H2), which would you recommend?

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  • Negative look ahead java

    - by venu
    I need an expression to capture a string like this "A"[A string that is NOT atleast 5 and atmost 6 digits]"B", In other words capture anything that is NOT the following A[0-9][0-9][0-9][0-9][0-9]B A[0-9][0-9][0-9][0-9][0-9][0-9]B I have tried the negative look ahead regex = "a((?![0-9]{5,6}).)*d" ; But it fails to capture all scenarios. Please help venu

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  • odd behavior with java collections of parameterized Class objects

    - by Paul
    Ran into some questionable behavior using lists of parameterized Class objects: ArrayList<Class<String>> classList = new ArrayList<Class<String>>(); classList.add(Integer.class); //compile error Class intClass = Integer.class; classList.add(intClass); //legal apparently, as long as intClass is not parameterized Found the same behavior for LinkedList, haven't tried other collections. Is it like this for a reason? Or have I stumbled on something?

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  • java.lang.classcastExcption

    - by Tara Singh
    Hi, I have an array list of objects in my application. private static ArrayList<Player> userList=new ArrayList<Player>(); In my application, I am converting this list to byte array and then sending it to other clients. At client When I am trying to cast it back to the ArrayList, its giving me casting error. I am doing this in client side after receiving this list as byte array: ArrayList<Player> pl = (ArrayList<Player>) toObject(receivedByteArray); where toObject is my function to convert the byte array to object; Any Suggestions please !!! Thanks.

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  • Java : Singleton class instances in a Web based Application

    - by Preethi Jain
    I have this Singleton class inside a Web Application . public class MyDAO { private static MyDAO instance; private MyDAO() { } public static MyDAO getInstance() { if (instance == null) { instance = new MyDAO(); } return instance; } I will access it this way public void get_Data() { MyDAO dao = MyDAO.getInstance(); } How many Objects of MyDAO class will be created if there are 3 Users accessing the Application ?? Will there be one instance of MyDAO per User ??

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  • Exception and Inheritance in JAVA

    - by user1759950
    Suppose we have this problem public class Father{ public void method1(){...} } public class Child1 extends Father{ public void method1() throws Exception{ super.method1(); ... } } Child1 extends Father and override method1 but given implementation Child1.method1 now throws a exception, this wont compile as override method can't throw new exceptions. What is the best solution? Propagate the required exception to the Father.. to me this is against encapsulation, inheritance and general OOP ( the father potentially throw and exception that will never happen ) Use a RuntimeException instead? This solution wont propagate the Exception to the father but I read In Oracle docs and others sources states class of exceptions should be used when "Client code cannot do anything" this is not that case, this exception will b useful to recover blablabla ( why is wrong to use RuntimeException instead? ) Other.. thanks, Federico

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  • Using Java method to display HTML code

    - by javArc
    Hey folks, ok so this is my problem, I need to display HTML code in a jsp, which wouldn't be a problem, except a requirement for this project is that we place all the code in a public class file and have seperate methods for each chunk(header, sidebar footer, etc). Now here's where i'm confused: "Your method should take the PrintWriter as a parameter to print out each line of HTML, and should have a return type of void" What does that mean? How do I pass the PrintWriter into a method? Does this make sense to anyone?

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  • best way to create UI java apps ?

    - by fwfwfw
    I've come across Netbeans but is there any tools out there that lets you build things event driven ? I'm looking for a feature like being able to drag and drop UI components, and add methods to buttons directly by double clicking it (kinda like visualbasic) and viewing the source.

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  • Java - Thread - Problem in one of the Sun's tutorial

    - by Yatendra Goel
    I was reading this Sun's tutorial on Thread. I found a block of code there which I think can be replaced by a code of fewer lines. I wonder why Sun's expert programmers followed that long way when the task can be accomplished with a code of fewer lines. I am asking this question so as to know that if I am missing something that the tutorial wants to convey. The block of code is as follows: t.start(); threadMessage("Waiting for MessageLoop thread to finish"); //loop until MessageLoop thread exits while (t.isAlive()) { threadMessage("Still waiting..."); //Wait maximum of 1 second for MessageLoop thread to //finish. t.join(1000); if (((System.currentTimeMillis() - startTime) > patience) && t.isAlive()) { threadMessage("Tired of waiting!"); t.interrupt(); //Shouldn't be long now -- wait indefinitely t.join(); } } threadMessage("Finally!"); I think that the above code can be replaced by the following: t.start(); t.join(patience); // InterruptedException is thrown by the main method so no need to handle it if(t.isAlive()) { // t's thread couldn't finish in the patience time threadMessage("Tired of waiting!"); t.interrupt(); t.join(); } threadMessage("Finally!");

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  • Method-Object pairs in Java

    - by John Manak
    I'd like to create a list of method-object pairs. Each method is a function returning a boolean. Then: foreach(pair) { if method evaluates to true { do something with the object } } One way of modelling this that I can think of is to have a class Constraint with a method isValid() and for each constraint produce an anonymous class (overriding the isValid() method). I feel like there could be a nicer way. Can you think of any?

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  • 2 bucks for !! java basic question

    - by Max
    How can I get a specific value from an object? I'm trying to get a value of an instance for eg. ListOfPpl newListOfPpl = new ListOfPpl(id, name, age); Object item = newListOfPpl; How can I get a value of name from an Object item?? Even if it is easy or does not interest you can anyone help me?? Edited: I was trying to build a binary tree contains the node of ListOfPpl, and need to sort it in the lexicographic. Here's my code for insertion on the node. Any clue?? public void insert(Object item){ Node current = root; Node follow = null; if(!isEmpty()){ root = new Node(item, null, null); return; }boolean left = false, right = false; while(current != null){ follow = current; left = false; right = false; //I need to compare and sort it if(item.compareTo(current.getFighter()) < 0){ current = current.getLeft(); left = true; }else { current = current.getRight(); right = true; } }if(left) follow.setLeft(new Node(item, null, null)); else follow.setRight(new Node(item, null, null)); }

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  • java switch case question

    - by hkvega
    public String sizeOfSupermarket() { String size; switch (this.numberOfProducts) { case (this.numberOfProducts > 5000): size = "Large"; break; case (this.numberOfProducts > 2000 && this.numberOfProducts < 5000): size = "Medium"; break; case (this.numberOfProducts < 2000): size = "Small"; break; } return size; } the above is wrong, how to write the compare statement in case statement?

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  • different for loops java

    - by Ayrton
    I'm having some difficulties with the following problem: I'm making a little game where you're at a specific spot and each spot has each some possible directions. The available directions are N(ord),E(ast),S,W . I use the function getPosDirections to get the possible directions of that spot. The function returns the directions into an ArrayList<String> e.g. for spot J3: [E,W] Now the game goes like this: 2 dice will be rolled so you get a number between 2 and 12, this number represents the number of steps you can make. What I want is an ArrayList of all the possible routes e.g.: I throw 3 and I'm currently at spot J3: [[E,N,E],[E,N,S],[E,S,E],[E,S,S],[W,N,E],[W,N,S],[W,S,E],[W,S,S]] How would obtain the last mentioned Array(list)?

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  • java beginner- in which folder should I place a "database.properties" file

    - by Arvind
    I read some tutorials on how to read data from a database.properties file- which basically stored key-value pairs. What i want to know is, in which folder should I place this file? Is it in the root (ie "src") or within a package... And how do I access this file, if it is placed in "src"- my code will be within a package (and the package's directory will be under src)- so how do I access the properties file, which is in "src", from a class within a package?

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  • Intercommunication between Java Chat Servers

    - by Pravingate
    I have a application in which I am using socket programming , having this(image) scenario. Where number of clients will try to connect Broadcast server. Now here I am managing load through LVS(Load balancer). so as a example shown in image, suppose 200 clients will wish to login for broadcast they will be distributed as 100 users on server 1 and another 100 users on server 2.clients will get connected to servers using TCP connection. Now I am maintaining user information on server side in arraylist which will be stored in heap memory,Now the problem is if client wish to broadcast to all logged in users, but that particular client is logged in server 1. and so client will not be able to broadcast another 100 users from server 2. Because both ther servers are unaware about each others state. please suggest to solve this scenario by whatever means you want.

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