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  • Is it possible to apply inheritance to a Singleton class?

    - by Bragaadeesh
    Hi, Today I faced one question in interview. Is it possible to apply inheritance concept on Singleton Classes. I said since the constructor is private, we cannot extend that Singleton class (can someone please validate this). Next thing he asked me is to apply inheritance on that Singleton class. So, I made the Singleton's constructor as protected thinking that child's constructor also has be protected. But I was wrong the child can have a modifier either equal to or higher than that. So, I asked him to give a real world example on such a case. He was not able to give me one and said that I cant ask questions and wanted me to tell whether this scenario is possible or not. I went kind of blank. My question here is, Is this possible? Even if its possible, what is the use of it? What real world scenario would demand such a use. Thanks

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  • ant conditions problem

    - by senzacionale
    I have problem with ant. I woul dlike to use conditions in ant. But i get error of: BUILD FAILED C:\Projekti\Projekt ANT\build.xml:412: Problem: failed to create task or type Cause: The name is undefined. Action: Check the spelling. Action: Check that any custom tasks/types have been declared. Action: Check that any / declarations have taken place. and this is code: <target name="test"> <input message="Write some text: " addproperty="foo" /> <if> <equals arg1="${foo}" arg2="bar" /> <then> <echo message="The value of property foo is 'bar'" /> </then> <elseif> <equals arg1="${foo}" arg2="foo" /> <then> <echo message="The value of property foo is 'foo'" /> </then> </elseif> <else> <echo message="The value of property foo is not 'foo' or 'bar'" /> </else> </if> </target>

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  • Javascript get li values and encode them

    - by bluedaniel
    At the moment I have two (maybe more) unordered lists which are sortable with jquery and ui. The things that work are that the lists are connected, items are draggable, items can be removed and a form that adds to the list. What I need however is a function that gets all the content for li items and json encode them ready to be sent off to some db function, or something. Im new to jquery however and cant find documentation for li items. Hope Ive explained this well. Daniel

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  • JarEntry.getSize() is returning -1 when the jar files is opened as InputStream from URL

    - by Reshma Donthireddy
    I am trying to read file from the JarInputStream and the size of file is returning -1. I am accessing Jar file from the URL as a inputStream. URLConnection con = url.openConnection(); JarInputStream jis = new JarInputStream(con.getInputStream()); JarEntry je = null; while ((je = jis.getNextJarEntry()) != null) { htSizes.put(je.getName(), new Integer((int) je.getSize())); if (je.isDirectory()) { continue; } int size = (int) je.getSize(); // -1 means unknown size. if (size == -1) { size = ((Integer) htSizes.get(je.getName())).intValue(); } byte[] b = new byte[(int) size]; int rb = 0; int chunk = 0; while (((int) size - rb) > 0) { chunk = jis.read(b, rb, (int) size - rb); if (chunk == -1) { break; } rb += chunk; } // add to internal resource hashtable htJarContents.put(je.getName(), baos.toByteArray()); }

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  • Any tools or techniques for validating constraints programmatically between databases?

    - by Brandon
    If you had two databases, that had two tables between them that would normally implement a one to one (or many to many) constraint but cannot since they are separate databases, how would you validate this relationship in an application or test? Is there a simple way to do this? For example, a tool or technique that can, given a constraint type, tables and fields, does the validation. I imagine that this isn't the first time this come up so I'm hoping people can share their solution. Thanks.

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  • How to inspect JSP request URL for String

    - by IAmYourFaja
    I have the following processor.jsp file: <% response.sendRedirect("http://buzz.example.com"); %> I want to change it so that it inspects the HTTP request URL for the presence of the word "fizz" and, if it exists, redirect the user to http://fizz.example.org instead. So something like: <% String reqUrl = request.getURL().toLowerCase(); String token = null; if(reqUrl.contains("fizz")) { token = "fizz"; } else { token = "buzz"; } String respUrl = "http://%%%TOKEN%%%.example.com".replace("%%%TOKEN%%%", token); response.sendRedirect(respUrl); %> However this doesn't work. Any ideas on what I should be using instead of request, or if I'm doing anything else wrong?

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  • Does close ever throw an IOException?

    - by TofuBeer
    After providing some answers here, and reading some comments, it would seem that, in practice IOException is never thrown on close for file I/O. Are there any cases in which calling close on a Stream/Reader/Writer actually throws an IOException? If an exception is actually thrown, how should it be dealt with?

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  • Is there a better way than a sequence of if's to handle events?

    - by Matt
    I recently ran across several objects implemented to handle events with a hard coded mapping using this pattern: public void handleEvent(Event event) { if(event.getCode() == SOME_STATIC_EVENT) doSomething(event); if(event.getCode() == ANOTHER_STATIC_EVENT) doSomethingElse(event); } where doSomething functions are implemented as methods of the same class. In hopes of striving for looser coupling, how would you suggest abstracting out this pattern? Also, what's the best approach for mapping 0..N functions to a fired event?

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  • Proper structure for dependency injection (using Guice)

    - by David B.
    I would like some suggestions and feedback on the best way to structure dependency injection for a system with the structure described below. I'm using Guice and thus would prefer solutions centered around it's annotation-based declarations, not XML-heavy Spring-style configuration. Consider a set of similar objects, Ball, Box, and Tube, each dependent on a Logger, supplied via the constructor. (This might not be important, but all four classes happen to be singletons --- of the application, not Gang-of-Four, variety.) A ToyChest class is responsible for creating and managing the three shape objects. ToyChest itself is not dependent on Logger, aside from creating the shape objects which are. The ToyChest class is instantiated as an application singleton in a Main class. I'm confused about the best way to construct the shapes in ToyChest. I either (1) need access to a Guice Injector instance already attached to a Module binding Logger to an implementation or (2) need to create a new Injector attached to the right Module. (1) is accomplished by adding an @Inject Injector injectorfield to ToyChest, but this feels weird because ToyChest doesn't actually have any direct dependencies --- only those of the children it instantiates. For (2), I'm not sure how to pass in the appropriate Module. Am I on the right track? Is there a better way to structure this? The answers to this question mention passing in a Provider instead of using the Injector directly, but I'm not sure how that is supposed to work. EDIT: Perhaps a more simple question is: when using Guice, where is the proper place to construct the shapes objects? ToyChest will do some configuration with them, but I suppose they could be constructed elsewhere. ToyChest (as the container managing them), and not Main, just seems to me like the appropriate place to construct them.

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  • Is there a design pattern to cut down on code duplication when subclassing Activities in Android?

    - by Daniel Lew
    I've got a common task that I do with some Activities - downloading data then displaying it. I've got the downloading part down pat; it is, of course, a little tricky due to the possibility of the user changing the orientation or cancelling the Activity before the download is complete, but the code is there. There is enough code handling these cases such that I don't want to have to copy/paste it to each Activity I have, so I thought to create an abstract subclass Activity itself such that it handles a single background download which then launches a method which fills the page with data. This all works. The issue is that, due to single inheritance, I am forced to recreate the exact same class for any other type of Activity - for example, I use Activity, ListActivity and MapActivity. To use the same technique for all three requires three duplicate classes, except each extends a different Activity. Is there a design pattern that can cut down on the code duplication? As it stands, I have saved much duplication already, but it pains me to see the exact same code in three classes just so that they each subclass a different type of Activity.

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  • DATA command hangs

    - by Tharban
    Hello, what can i do, if a Mailserver accepts a connection but does not return any data? The default javax.mail implementation just hangs indefinitley. Event setting the smtp.timeout does not help - it still hangs. I even tried to set a custom SocketFactory to set the sotimeouts and solinger directly, but it still hangs. Somehow the socket does get kept alive? But how? Thx for any ideas! Ciao, Nils

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  • Making an efficient algorithm

    - by James P.
    Here's my recent submission for the FB programming contest (qualifying round only requires to upload program output so source code doesn't matter). The objective is to find two squares that add up to a given value. I've left it as it is as an example. It does the job but is too slow for my liking. Here's the points that are obviously eating up time: List of squares is being recalculated for each call of getNumOfDoubleSquares(). This could be precalculated or extended when needed. Both squares are being checked for when it is only necessary to check for one (complements). There might be a more efficient way than a double-nested loop to find pairs. Other suggestions? Besides this particular problem, what do you look for when optimizing an algorithm? public static int getNumOfDoubleSquares( Integer target ){ int num = 0; ArrayList<Integer> squares = new ArrayList<Integer>(); ArrayList<Integer> found = new ArrayList<Integer>(); int squareValue = 0; for( int j=0; squareValue<=target; j++ ){ squares.add(j, squareValue); squareValue = (int)Math.pow(j+1,2); } int squareSum = 0; System.out.println( "Target=" + target ); for( int i = 0; i < squares.size(); i++ ){ int square1 = squares.get(i); for( int j = 0; j < squares.size(); j++ ){ int square2 = squares.get(j); squareSum = square1 + square2; if( squareSum == target && !found.contains( square1 ) && !found.contains( square2 ) ){ found.add(square1); found.add(square2); System.out.println( "Found !" + square1 +"+"+ square2 +"="+ squareSum); num++; } } } return num; }

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  • What is the correct approach to using GWT with persistent objects?

    - by dankilman
    Hi, I am currently working on a simple web application through Google App engine using GWT. It should be noted that this is my first attempt at such a task. I have run into to following problem/dilema: I have a simple Class (getters/setters and nothing more. For the sake of clarity I will refer to this Class as DataHolder) and I want to make it persistent. To do so I have used JDO which required me to add some annotations and more specifically add a Key field to be used as the primary key. The problem is that using the Key class requires me to import com.google.appengine.api.datastore.Key which is ok on the server side, but then I can't use DataHolder on the client side, because GWT doesn't allow it (as far as I know). So I have created a sister Class ClientDataHolder which is almost identical, though it doesn't have all the JDO annotations nor the Key field. Now this actually works but It feels like I'm doing something wrong. Using this approach would require maintaining to separate classes for each entity I wish to have. So my question is: Is there a better way of doing this? Thank you.

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  • Read a file with 2048 bytes

    - by Suresh S
    Guys i have a file which has only one line. The file has no encoding it is a simple text file with single line. For every 2048 byte in a line , there is new record of 151 byte (totally 13*151 byte = 1945 records + 85 byte empty space). similarly for the next 2048 bytes. What is the best file i/o to use? i am thinking of reading 2048 bytes from file and storing it in an array . while (offset < fileLength &&(numRead=in.read(recordChunks, offset,alength)) >= 0) { } how can i get from the read statement only 2048 bytes at a time . i am getting IndexOutofBoundException.

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  • How to display image in Swing? in textarea?

    - by Nitesh Panchal
    Hello, I am creating a chat application using JApplet. I have a TextArea where all chat messages go. Everything in working fine and smooth just as you would expect a basic chat application to do. Now i want to add support for gestures. I wanted to know, how can we show an icon in textarea? it only takes string in append() method. Thanks in advance :)

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  • Buffering db inserts in multithreaded program

    - by Winter
    I have a system which breaks a large taks into small tasks using about 30 threads as a time. As each individual thread finishes it persists its calculated results to the database. What I want to achieve is to have each thread pass its results to a new persisance class that will perform a type of double buffering and data persistance while running in its own thread. For example, after 100 threads have moved their data to the buffer the persistance class then the persistance class swaps the buffers and persists all 100 entries to the database. This would allow utilization of prepared statements and thus cut way down on the I/O between the program and the database. Is there a pattern or good example of this type of multithreading double buffering?

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  • Twitter4J - Looking up profile details without logging in

    - by wvd
    Hello all, I've been using Twitter4J for a quite a while now, but I can't seem to find this particular feature. I want to be able to search on a name, and when the certain user is on twitter, I want to retrieve basic information such as tweets, followers (like you can access via http) - but how to do is in Twitter4J? Neither the code examples or the source could help me. Thanks, William van Doorn

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  • How to copy an object by value, not by reference

    - by Blankman
    I want to make a copy of an object, then after some logic, re-assign the original object the value of the copy. example: User userCopy = //make a copy foreach(...) { user.Age = 1; user.ID = -1; UserDao.Update(user) user = userCopy; } I don't want a copy by reference, it has to be a copy by value. The above is just a sample, not how I really want to use it but I need to learn how to copy by value.

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  • Spring MVC: Where to place validation and how to validation entity references.

    - by arrages
    Let's say I have the following command bean for creating a user: public class CreateUserCommand { private String userName; private String email; private Integer occupationId; pirvate Integer countryId; } occupationId and countryId are drop down selected values on the form. They map to an entity in the database (Occupation, Country). This command object is going to be fed to a service facade like so: userServiceFacade.createUser(CreateUserCommand command); This facade will construct a user entity to be sent to the actual service. So I suppose that in the facade layer I will have to make several dao calls to map all the lookup properties of the User entity. Based on this what is the best strategy to validate that occupationId and countryId map to real entities? Where is the best place to perform this validation? There is the spring validator but I am not sure this is the best place for this, for one I am wary of this method as validation is tied to the web tier, but also that means I would need to make the dao calls in the validator for validation but I would need to call the dao's in the facade layer again when the command - entity translation occurs. Is there anything I can do better? Thanks.

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  • passing reference of class to another class android error

    - by prolink007
    I recently asked the precursor to this question and had a great reply. However, when i was working this into my android application i am getting an unexpected error and was wondering if everyone could take a look at my code and help me see what i am doing wrong. Link to the initial question: passing reference of class to another class My ERROR: "The constructor ConnectDevice(new View.OnClickListener(){}) is undefined" The above is an error detected by eclipse. Thanks in advance! Below are My code snippets: public class SmartApp extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.intro); final Button connectDeviceButton = (Button) findViewById(R.id.connectDeviceButton); connectDeviceButton.setOnClickListener( new View.OnClickListener() { @Override public void onClick(View v) { Thread cThread = new Thread(new ConnectDevice(this)); cThread.start(); } }); } } public class ConnectDevice implements Runnable { private boolean connected; private SmartApp smartAppRef; private ObjectInputStream ois; public ConnectDevice(SmartApp smartAppRef) { this.smartAppRef = smartAppRef; } }

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  • How to detect if a form input element of type file is empty

    - by Ankur
    I have some code which reads a file through a form field of type file <input type="file" ... /> I want to give the user another option of providing a url to a file rather than having to upload it as many are already online. How can I detect when this field is empty on the server side. I am using Apache Commons FileUpload FileItemStream item = iter.next(); name = item.getFieldName(); stream = item.openStream(); if(!item.isFormField()){ if(item.toString()!=""){ .... I need to detect when item is empty. The above code doesn't work, nor does using: if(item.equals(null)){ ....

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