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Immutability of big objects

- by Malax

Hi StackOverflow! I have some big (more than 3 fields) Objects which can and should be immutable. Every time I run into that case i tend to create constructor abominations with long parameter lists. It doesn't feel right, is hard to use and readability suffers. It is even worse if the fields are some sort of collection type like lists. A simple addSibling(S s) would ease the object creation so much but renders the object mutable. What do you guys use in such cases? I'm on Scala and Java, but i think the problem is language agnostic as long as the language is object oriented. Solutions I can think of: "Constructor abominations with long parameter lists" The Builder Pattern Thanks for your input!

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Interview question: Check if one string is a rotation of other string.

- by Webdev

A friend of mine was asked the following question today at interview for the position of software developer. Given two string s1 and s2 how will you check if s1 is a rotated version of s2 ? Example: if s1 = "stackoverflow"; then the following are some of its rotated versions: "tackoverflows" "ackoverflowst" "overflowstack" where as "stackoverflwo" is not a rotated version. The answer he gave was: Take s2 and find the logest prefix that is a substring of s1, that will give you the point of rotation. Once you find that point, break s2 at that point to get s2a and s2b, then just check if concatenate(s2a,s2b) == s1 It looks like a good solution to me and my friend. But the interviewr though otherwise. He asked for a simpler solution. Please help me by telling how would you do this in Java/C/C++ ? Thanks in advance.

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resizing arrays when close to memory capacity

- by user548928

So I am implementing my own hashtable in java, since the built in hashtable has ridiculous memory overhead per entry. I'm making an open-addressed table with a variant of quadratic hashing, which is backed internally by two arrays, one for keys and one for values. I don't have the ability to resize though. The obvious way to do it is to create larger arrays and then hash all of the (key, value) pairs into the new arrays from the old ones. This falls apart though when my old arrays take up over 50% of my current memory, since I can't fit both the old and new arrays in memory at the same time. Is there any way to resize my hashtable in this situation Edit: the info I got for current hashtable memory overheads is from here How much memory does a Hashtable use? Also, for my current application, my values are ints, so rather than store references to Integers, I have an array of ints as my values.

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Problem in generation of custom classes at web service client

- by user443324

I have a web service which receives an custom object and returns another custom object. It can be deployed successfully on GlassFish or JBoss. @WebMethod(operationName = "providerRQ") @WebResult(name = "BookingInfoResponse" , targetNamespace = "http://tlonewayresprovidrs.jaxbutil.rakes.nhst.com/") public com.nhst.rakes.jaxbutil.tlonewayresprovidrs.BookingInfoResponse providerRQ(@WebParam(name = "BookingInfoRequest" , targetNamespace = "http://tlonewayresprovidrq.jaxbutil.rakes.nhst.com/") com.nhst.rakes.jaxbutil.tlonewayresprovidrq.BookingInfoRequest BookingInfoRequest) { com.nhst.rakes.jaxbutil.tlonewayresprovidrs.BookingInfoResponse BookingInfoResponse = new com.nhst.rakes.jaxbutil.tlonewayresprovidrs.BookingInfoResponse(); return BookingInfoResponse; } But when I create a client for this web service, two instances of BookingInfoRequest and BookingInfoResponse generated even I need only one instance. This time an error is returned that says multiple classes with same name are can not be possible....... Here is wsdl..... <?xml version='1.0' encoding='UTF-8'?><definitions xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd" xmlns:wsp="http://www.w3.org/ns/ws-policy" xmlns:wsp1_2="http://schemas.xmlsoap.org/ws/2004/09/policy" xmlns:wsam="http://www.w3.org/2007/05/addressing/metadata" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:tns="http://demo/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://schemas.xmlsoap.org/wsdl/" targetNamespace="http://demo/" name="DemoJAXBParamService"> <wsp:Policy wsu:Id="DemoJAXBParamPortBindingPolicy"> <ns1:OptimizedMimeSerialization xmlns:ns1="http://schemas.xmlsoap.org/ws/2004/09/policy/optimizedmimeserialization" /> </wsp:Policy> <types> <xsd:schema> <xsd:import namespace="http://tlonewayresprovidrs.jaxbutil.rakes.nhst.com/" schemaLocation="http://localhost:31133/DemoJAXBParamService/DemoJAXBParamService?xsd=1" /> </xsd:schema> <xsd:schema> <xsd:import namespace="http://tlonewayresprovidrs.jaxbutil.rakes.nhst.com" schemaLocation="http://localhost:31133/DemoJAXBParamService/DemoJAXBParamService?xsd=2" /> </xsd:schema> <xsd:schema> <xsd:import namespace="http://tlonewayresprovidrq.jaxbutil.rakes.nhst.com/" schemaLocation="http://localhost:31133/DemoJAXBParamService/DemoJAXBParamService?xsd=3" /> </xsd:schema> <xsd:schema> <xsd:import namespace="http://tlonewayresprovidrq.jaxbutil.rakes.nhst.com" schemaLocation="http://localhost:31133/DemoJAXBParamService/DemoJAXBParamService?xsd=4" /> </xsd:schema> <xsd:schema> <xsd:import namespace="http://demo/" schemaLocation="http://localhost:31133/DemoJAXBParamService/DemoJAXBParamService?xsd=5" /> </xsd:schema> </types> <message name="providerRQ"> <part name="parameters" element="tns:providerRQ" /> </message> <message name="providerRQResponse"> <part name="parameters" element="tns:providerRQResponse" /> </message> <portType name="DemoJAXBParam"> <operation name="providerRQ"> <input wsam:Action="http://demo/DemoJAXBParam/providerRQRequest" message="tns:providerRQ" /> <output wsam:Action="http://demo/DemoJAXBParam/providerRQResponse" message="tns:providerRQResponse" /> </operation> </portType> <binding name="DemoJAXBParamPortBinding" type="tns:DemoJAXBParam"> <wsp:PolicyReference URI="#DemoJAXBParamPortBindingPolicy" /> <soap:binding transport="http://schemas.xmlsoap.org/soap/http" style="document" /> <operation name="providerRQ"> <soap:operation soapAction="" /> <input> <soap:body use="literal" /> </input> <output> <soap:body use="literal" /> </output> </operation> </binding> <service name="DemoJAXBParamService"> <port name="DemoJAXBParamPort" binding="tns:DemoJAXBParamPortBinding"> <soap:address location="http://localhost:31133/DemoJAXBParamService/DemoJAXBParamService" /> </port> </service> </definitions> So, I want to know that how to generate only one instance(I don't know why two instances are generated at client side?). Please help me to move in right direction.

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JAX-RS implementation of link/element expansion?

- by Jimmy

While reading documentation of Google Data API and Atlassian REST API, I found interesting functionality - link (or title, element expansion) - http://bit.ly/i3rKMw. I would like to implement this functionality in my Java project of web service server for our IS, but I can't find any proper solution or advices for implementation. My project is quite big with many services so I need some robust and most automated solution. I was thinking about how to implement it like an extension for RESTEasy and JAXB, but it seems to be very complicated. Do you know some opensource projects which implements this functionality or any advices which could help me?

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Should GSON ignore varying types if they're not used in a class?

- by loeschg

I'm making an API call that returns JSON which has a particular field which either returns false or a map depending on content. It's a field that I don't care about. I expected GSON to ignore this particular field, though it doesn't seem to be. The object generation fails with the following message: com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected a string but was BEGIN_OBJECT at line 1 column 403560 I've seen this particular question (Gson deserialize json with varying value types). I want to make sure I need to make a custom deserializer before doing so. I'm wondering if I may have another issue. edit: Example: "anonymous_flag": { } vs "anonymous_flag": "yes" Another Edit: I actually had the field in my model object... I was referencing the wrong class. Judge away :)

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Why setValue at not working on Jtable?

- by Nitz

Hey Guys I am doing project on java. In one of the class, I am working on jtable. Now what i am doing is, In the table data will be loaded from the database. Now i want to change some value at some exact row and column. so for that i am using jtable's setValue function. which is like this.... grayCardTbl.setValueAt(Float.valueOf(String.valueOf(pdiff)),1,4); I have checked the "pdiff" variable, it is perfect. i had total 5 columns and 10 rows. So now problem with rowindex and column index. and after this i have also refresh the table. but still it is not reflecting on table.

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What is the JVM Scheduling algorithm ?

- by IHawk

Hello ! I am really curious about how does the JVM work with threads ! In my searches in internet, I found some material about RTSJ, but I don't know if it's the right directions for my answers. I also found this topic in sun's forums, http://forums.sun.com/thread.jspa?forumID=513&threadID=472453, but that's not satisfatory. Can someone give me some directions, material, articles or suggestion about the JVM scheduling algorithm ? I am also looking for information about the default configurations of Java threads in the scheduler, like 'how long does it take for every thread' in case of time-slicing. And this stuff. I would appreciate any help ! Thank you !

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android set hidden the keybord on press enter (in a EditText)

- by user119333

Hi, When my user press "ENTER" on the virtual android "user validate entry!" keybord my keybord stay visible ! (Why?) Here my Java code... private void initTextField() { entryUser = (EditText) findViewById(R.id.studentEntrySalary); entryUser.setOnKeyListener(new OnKeyListener() { public boolean onKey(View v, int keyCode, KeyEvent event) { if (event.getAction() == KeyEvent.ACTION_DOWN) { switch (keyCode) { case KeyEvent.KEYCODE_DPAD_CENTER: case KeyEvent.KEYCODE_ENTER: userValidateEntry(); return true; } } return true; } }); } private void userValidateEntry() { System.out.println("user validate entry!"); } ... here my View <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="wrap_content" android:layout_height="wrap_content"> <EditText android:id="@+id/studentEntrySalary" android:text="Foo" android:layout_width="wrap_content" android:layout_height="wrap_content" /> </LinearLayout> Maybe something wrong on my virtual device ?

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jsp TextField binding

- by user72185

I have a panel in my Page1.jsp: <webuijsf:panelLayout binding="#{Page1.dynamicFieldsPanel}" id="dynamicFieldsPanel" -rave-layout: grid"/> Then I have this in Page1.java: private PanelLayout dynamicFieldsPanel = new PanelLayout(); public void setDynamicFieldsPanel(PanelLayout pl) { this.dynamicFieldsPanel = pl; } public PanelLayout getDynamicFieldsPanel() { TextField textField = new TextField(); this.dynamicFieldsPanel.getChildren().add(textField); return dynamicFieldsPanel; } How do I bind my dynamic TextField to something so I can retrieve the value entered by the user?

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How can I determine if a file I want to read from actually exists?

- by Imray

I'm learning Java, and I'm trying to write a program that can read from a .ser file, which I've already created with a writeTo method. I want to know a given file exists in the system before I tell the program to read from it. My code looks like this: public boolean readFromSerializedFile(String fileName){ FileInputStream fileInStream = null; ObjectInputStream objectInStream = null; try{ fileInStream = new FileInputStream(fileName); objectInStream = new ObjectInputStream(fileInStream); Is there a simple way I can determine if the file with the name of the parameter exists in the root directory (or wherever else specified)?

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Replace underscore between words (reg.exp)

- by lasseespeholt

Hey, I need a regular expression to solve the following problem (links to similar problems is also appreciated, related tutorials etc.): __some_words_a_b___ => __some words a b___ ____ => ____ So I want underscores between words to be replaced with space and keep leading and trailing underscores. I found this: ^[ \t]+|[ \t]+$ and I guess it most be something like that. I will use it in jQuery, Java (stdlibs) and maybe XSLT. Addition: The sentences do not necessarily start with underscores or ends with underscores. It is also possible that a sentence ain't containing underscores at all. Best regards Lasse Espeholt

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what happens to running/blocked runnables when executorservice is shutdown()

- by prmatta

I posted a question about a thread pattern today, and almost everyone suggested that I look into the ExecutorService. While I was looking into the ExecutorService, I think I am missing something. What happens if the service has a running or blocked threads, and someone calls ExecutorService.shutdown(). What happens to threads that are running or blocked? Does the ExecutorService wait for those threads to complete before it terminates? The reason I ask this is because a long time ago when I used to dabble in Java, they deprecated Thread.stop(), and I remember the right way of stopping a thread was to use sempahores and extend Thread when necessary: public void run () { while (!this.exit) { try { block(); //do something } catch (InterruptedException ie) { } } } public void stop () { this.exit = true; if (this.thread != null) { this.thread.interrupt(); this.thread = null; } } How does ExecutorService handle running threads?

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How to see what objects lie in which generation in YourKit?

- by prams

I am using YourKit (11.0) to try to profile my j2ee app. The app uses java 6 and running on 64-bit linux (centos). I was told that YourKit possibly tells us which objects exist in which generation (eden, old, etc) at any given point of time. On a side note, I am trying to chase a problem where memory usage keeps increasing until a major collection happens (every 4 hrs) and I am suspicious about few particular objects, so I am interested to know where those objects lie at different times. Fortunately I know lot of memory is being consumed in one particular area of code (so other objects are possibly directly being put into the old gen), but don't exactly know how much of that memory is being put into eden space, how much is being collected by the minor collections, etc. Thanks.

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How to handle updating JDO class definitions on Google App Engine

- by Spines

I'm using the Google app engine and JDO. What is the best way to update a JDO class definition without having to wipe the data store contents first? I'm not sure if this is specific to JDO on GAE, but I noticed that when I simply change the name of one of my persistent fields from svotes to votes, an exception is thrown (java.lang.NoSuchFieldError: svotes). I expect once my site goes live I might want to make some changes to my JDO class definitions, such as adding a field or something. Any suggestions for how to update the data definitions without having to wipe the database?

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Finding the average of two number using classes and methods

- by Have alook

I want to use methods inside class. Q: find the average of two number using classes and methods. import java.util.*; class aaa { int a,b,sum,avrg; void average() { System.out.println("The average is ="+avrg); avrg=(sum/2); } } class ave { public static void main(String args[]){ aaa n=new aaa(); Scanner m=new Scanner(System.in); System.out.println("write two number"); n.a=m.nextInt(); n.b=m.nextInt(); n.average(); } }

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How to deal with extra space characters while Reading a CSV file?

- by Ravi Dutt

I am reading a CSV file with CSV Open Source API. as shown below: Java Code:--> CSVReader reader = new CSVReader(new FileReader(filePath),'\n'); String[] values; if((read=(reader.readNext()))!=null) { values = (read[0].split(" (?=([^\"]*\"[^\"]*\")*[^\"]*$)",-1)).length; } // code ends here When I read this CSV file line by line and split that line with delimiter. Then after spliting values each value I get contains extra space character after each character in String. Suppose value in file is like "ABC" and I got this after reading from CSV file reader as " A B C " . I used removeAll("\s+","") on each value even after it is not working. Thank You in Advance.

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Any reason not to always log stack traces?

- by Chris Knight

Encountered a frustrating problem in our application today which came down to an ArrayIndexOutOfBounds exception being thrown. The exception's type was just about all that was logged which is fairly useless (but, oh dear legacy app, we still love you, mostly). I've redeployed the application with a change which logs the stack trace on exception handling (and immediately found the root cause of the problem) and wondered why no one else did this before. Do you generally log the stack trace and is there any reason you wouldn't do this? Bonus points if you can explain (why, not how) the rationale behind having to jump hoops in java to get a string representation of a stack trace!

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Java2D: Fill a convex rounded polygon (QuadCurves)

- by Martijn Courteaux

Hi, If I have a QuadCurve like this (+ = node): + + \ ./ +--?? And I fill it in Java 2D the result is something like this: (x = colored) +xxxxxxxxx+ \xxxxxx./ +--?? But I want to color the other side: + + x\ ./x xxx +--??xx xxxxxxxxxxx This succeeds by drawing a rectangle around the curve in the color I want to color the other side and then fill the curve with the background color. But this isn't good enough to fill a convex rounded (based on QuadCurves) polygon. In case of some coordinates for the rectangles (as explained in the trick I used) overlap other pieces of the polygon. Here are two images (the green area is my polygon): So, the question is simple: "How can I color a shape build of curves?" But to the answer will not be simple I think... Any advice would be VERY VERY appreciated. Thanks in advance. Maybe I'm going to make a bounty for this question if I don't get an answer

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How to keep Hibernate mapping use under control as requirements grow

- by David Plumpton

I've worked on a number of Java web apps where persistence is via Hibernate, and we start off with some central class (e.g. an insurance application) without any time being spent considering how to break things up into manageable chunks. Over time as features are added we add more mappings (rates, clients, addresses, etc.) and then amount of time spent saving and loading an insurance object and everything it connects to grows. In particular you get close to a go-live date and performance testing with larger amounts of data in each table is starting to demonstrate that it's all too slow. Obviously there are a number of ways that we could attempt to partition things up, e.g. map only the client classes for the client CRUD screens, etc., which would have been better to get in place earlier rather than trying to work it in at the end of the dev cycle. I'm just wondering if there are recommendations about ways to handle/mitigate this.

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Manage duplicate jar files using ant and ivy.

- by lawardy

HI, I am using ant build script to build my java app and utilizing Ivy to manage its dependency. As my application is dependent/subset of other application(Main App), when running it, I set the classpath to point to lib jars of the Main App. As I tried to build the kit using ant and ivy, it includes/retrieve all the jars that is required as specified in ivy.xml The problem is, some of the jar files are duplicated with with jars file in the main app folders. Is there a way to set the classpath in build.xml to ignore retrieving jar files that already exist in the main app's lib folder. Thanks

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How can I easily run different configurations in Eclipse?

- by Roman

I have an Java applications which I would like to run with different values of input parameters (specified in the command line). In "Run - Run Configurations" I have created different configurations corresponding to different values of the input arguments. I can run these configurations in the same way (throw "Run - Run Configurations"). But in these case I have to perform to many actions (clicks) to run a particular configuration. Is there a easier (faster) way to do that? For example I expect that I can do it throw "Run - Run as" but in the drop-dawn menu of the "Run as" I see "(Not Applicable)".

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Too many open connections... Did I mess up something?

- by Legend

I am developing a plugin (for a Bittorrent client named Azureus programmed in Java) that lets me add peers into the current list from which it is downloading. Everything was working fine until yesterday when I started getting these weird errors: DEBUG::Thu Apr 15 10:45:40 CET 2010::org.gudy.azureus2.core3.peer.impl.control.PEPeerControlImpl::addPeer::795: Injected peer 90.35.126.126:33064 was not added - Too many connections DEBUG::Thu Apr 15 10:48:40 CET 2010::org.gudy.azureus2.core3.peer.impl.control.PEPeerControlImpl::addPeer::795: Injected peer 80.25.126.126:33064 was not added - Too many connections DEBUG::Thu Apr 15 10:52:40 CET 2010::org.gudy.azureus2.core3.peer.impl.control.PEPeerControlImpl::addPeer::795: Injected peer 90.35.126.126:33064 was not added - Too many connections I am thinking I messed up something with the TCP sockets. Does anyone know why this could be happening?

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How to check connection leak using regular expression ?

- by gauravkarnatak

I have to check connection leak in my application i.e. open connections which have not been closed. After searching, after I found out that a thousands times connections have been opened but I can't manually go to each and every code fragment and check for connection close thing. I think, it could be possible using a regular expression but the fact is, I am not that well versed with regex that I could write one. Please suggest a regular expression for checking in a no of java files that a opened connection has been closed or not. My code pattern is something like this. try { /* Some code goes here */ con = EJBUtil.getConnection(JNDI_NAME); /* Some code goes here */ } finally { /* Some code goes here */ DBUtil.close(con); or closeConnection.close(con); /* Some code goes here */ }

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Remote Development Workflow with Tomcat and Eclipse

- by Smithers

Currently, I have tomcat installed on the production server to serve my java webapps. I develop in eclipse at my personal workstation and then I use an ant script to build the project into a war file and deploy that on the server. This setup works well when I am on the same network as the server because deploying is almost instantaneous. However, now that I am working remotely uploading the war file to the server is slow and in most cases very redundant (there are about .5 GB of static media included in the war file). Is there a better way to update my webapp on tomcat from eclipse and if so what are the best options for implementing such a solution with minimal effort?

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