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• Using low level api for datastore in google app engine ? is it bad ?

  - by Chez

  There is little documentation on how to use the low level api for datastore and quite a lot on JPA and JDO and how it translates to it. My question is: is there any advantage in coding against the JPA or JDO specs instead of accessing directly the low level api for datastore ? From an initial look, it seems simple and straight forward but I am not sure if there are good reasons why not to do it. Thanks Cx

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• getting node value exception

  - by Aswan

  Hi Folks <amount currency="USD">1000500</amount> while parsing above string i am getting only attribute value .when i try to get node value null pointer exception for getting node value using NodeList amountList= estimateElement.getElementsByTagName("amount"); Element amtElement= (Element)amountList.item(0); String amount=amtElement.getFirstChild().getnodevalue() Thanks in advance Aswan

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• Why we don't have to add try-catch to a RuntimeException ?

  - by M.H

  Hi,I want to ask why we don't have to add try-catch block to a RuntimeException while we should do that with other exceptions ?I mean like : public class Main { public static void main(String[] args) { throw new RuntimeException(); } }

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• Where should I put interface?

  - by Roman

  I program a class in which I have a method which takes an callback object from an external software. At the moment Eclipse says that it does not know the type of the object I gave as argument (it is expectable since I do not specify this type, it's done by the external software). So, I think I need to write an interface for the object which I give as an argument to my method. In this respect I have two questions. Is it really so? Can I solve the mentioned problem in the mentioned way. If it is the case, where should I put this interface? In the same file where my class is? In the class? Outside of the class?

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• Is fetching an object by String key be faster than a Key key? (GAE/J)

  - by user259349

  Thats pretty much the question. Are there any other concerns i should be aware of?

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• Trying to packetize TCP with non-blocking IO is hard! Am I doing something wrong?

  - by Ricket

  Oh how I wish TCP was packet-based like UDP is! But alas, that's not the case, so I'm trying to implement my own packet layer. Here's the chain of events so far (ignoring writing packets) Oh, and my Packets are very simply structured: two unsigned bytes for length, and then byte[length] data. (I can't imagine if they were any more complex, I'd be up to my ears in if statements!) Server is in an infinite loop, accepting connections and adding them to a list of Connections. PacketGatherer (another thread) uses a Selector to figure out which Connection.SocketChannels are ready for reading. It loops over the results and tells each Connection to read(). Each Connection has a partial IncomingPacket and a list of Packets which have been fully read and are waiting to be processed. On read(): Tell the partial IncomingPacket to read more data. (IncomingPacket.readData below) If it's done reading (IncomingPacket.complete()), make a Packet from it and stick the Packet into the list waiting to be processed and then replace it with a new IncomingPacket. There are a couple problems with this. First, only one packet is being read at a time. If the IncomingPacket needs only one more byte, then only one byte is read this pass. This can of course be fixed with a loop but it starts to get sorta complicated and I wonder if there is a better overall way. Second, the logic in IncomingPacket is a little bit crazy, to be able to read the two bytes for the length and then read the actual data. Here is the code, boiled down for quick & easy reading: int readBytes; // number of total bytes read so far byte length1, length2; // each byte in an unsigned short int (see getLength()) public int getLength() { // will be inaccurate if readBytes < 2 return (int)(length1 << 8 | length2); } public void readData(SocketChannel c) { if (readBytes < 2) { // we don't yet know the length of the actual data ByteBuffer lengthBuffer = ByteBuffer.allocate(2 - readBytes); numBytesRead = c.read(lengthBuffer); if(readBytes == 0) { if(numBytesRead >= 1) length1 = lengthBuffer.get(); if(numBytesRead == 2) length2 = lengthBuffer.get(); } else if(readBytes == 1) { if(numBytesRead == 1) length2 = lengthBuffer.get(); } readBytes += numBytesRead; } if(readBytes >= 2) { // then we know we have the entire length variable // lazily-instantiate data buffers based on getLength() // read into data buffers, increment readBytes // (does not read more than the amount of this packet, so it does not // need to handle overflow into the next packet's data) } } public boolean complete() { return (readBytes > 2 && readBytes == getLength()+2); } Basically I need feedback on my code. Please suggest any improvements. Even overhauling my entire system would be okay, if you have suggestions for how better to implement the whole thing. Book recommendations are welcome too; I love books. I just get the feeling that something isn't quite right.

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• How to detect that code is running inside eclipse IDE

  - by DD

  How to detect that code is running inside eclipse IDE

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• Please help with my twodimensional array source code

  - by Baiba

  Here is what i have done but i have some questions: class masivins { public static void main (String args[]) { int mas[][] = {{0, 2, 7, 0, 8, 5, 3}, {0, 4, 0, 6, 0, 0, 0}, {0, 0, 0, 0, 3, 0, 0}, {7, 0, 0, 9, 1, 0, 7}, {5, 0, 4, 0, 0, 2, 0}}; int nulmas[] = new int [7]; int nul=0; for(int j=0; j<7; j++) { nul=0; for(int i=0; i<5; i++) { if(mas[i][j]==0) { nul++; } } nulmas[j]=nul; } for(int i=0; i<5; i++) { for(int j=0; j<7; j++) { System.out.println(mas[i][j]); } System.out.println(); } System.out.println(); for(int i=0; i<5; i++) { System.out.println("Zeros in each array column: " + nulmas[i]); } System.out.println(); } } so my questions are: 1) why after running project there are only 5 "Zeros in each array column....." shown? 2) what and where i need to change in this code to get out the number of column in which zeros are least?

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• Solr automatic startup script

  - by Camran

  I have followed this tutorial: http://wiki.apache.org/solr/SolrJetty But I cant get it working. I don't know what to put in the etc/defaults/jetty file Does anybody know how to configure this? I have Ubuntu 9 Server. Thanks

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• LinkedList insert tied to inserted object

  - by wrongusername

  I have code that looks like this: public class Polynomial { List<Term> term = new LinkedList<Term>(); and it seems that whenever I do something like term.add(anotherTerm), with anotherTerm being... another Term object, it seems anotherTerm is referencing the same thing as what I've just inserted into term so that whenever I try to change anotherTerm, term.get(2) (let's say) get's changed too. How can I prevent this from happening?

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• Is there a file diff tool that allows for exceptions?

  - by Kevin

  We currently use Beyond Compare 3.0 and I am quite pleased with it. However, it would be great if I could easily specify an exclusion for a specific one-time case. This is needed when I am doing a code review of some refactoring. For instance: Old code doSomething(ConstantsInterface.FOOBAR); New code: doSomething(BetterEnumeration.FOOBAR); In this case, I have hundreds of changes that I am reviewing that are essentially all the same exact change and I just want to see the exceptions. It would be great if I could easily specify an exception that indicates these two cases are equal. I know of a way to do it in the grammar, but it is tedious and cumbersome in the case where there are ten or so exceptions. Any other tips?

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• Practicing inserting data into an array by using binary search, few problems

  - by HelpNeeder

  I'm trying to create a method which inserts and then sort elements in form of binary form. The problem I am experiencing that my code doesn't insert data correctly which means that output does not appear to be in order at all. The list is not organized, and data is added in order that is being inserted. Now, 2 questions, what am I doing wrong here? And how to fix this? public void insertBinarySearch(long value) // put element into array { int j = 0; int lower = 0; int upper = elems-1; int cur = 0; while (cur < elems) { curIn = (lower + upper ) / 2; if(a[cur] < value) { j = cur + 1; break; } else if(a[cur] > value) { j = cur; break; } else { if(a[cur] < value) lower = cur + 1; else upper = cur - 1; } } for(int k = elems; k > j; k--) a[k] = a[k-1]; a[j] = value; elems++; }

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• Design issue when having classes implement different interfaces to restrict client actions

  - by devoured elysium

  Let's say I'm defining a game class that implements two different views: interface IPlayerView { void play(); } interface IDealerView { void deal(); } The view that a game sees when playing the game, and a view that the dealer sees when dealing the game (this is, a player can't make dealer actions and a dealer can't make player actions). The game definition is as following: class Game : IPlayerView, IDealerView { void play() { ... } void deal() { ... } } Now assume I want to make it possible for the players to play the game, but not to deal it. My original idea was that instead of having public Game GetGame() { ... } I'd have something like public IPlayerView GetGame() { ... } But after some tests I realized that if I later try this code, it works: IDealerView dealerView = (IDealerView)GameClass.GetGame(); this works as lets the user act as the dealer. Am I worrying to much? How do you usually deal with this patterns? I could instead make two different classes, maybe a "main" class, the dealer class, that would act as factory of player classes. That way I could control exactly what I would like to pass on the the public. On the other hand, that turns everything a bit more complex than with this original design. Thanks

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• Does Socket open another thread? Does it return something?

  - by Roman

  In the client application I call new Socket(serverIP,serverPort). As a result the client application sends a request to the server application to open a socket. Does it start a new thread? I mean which of the following is true? Client application sends a request and immediately starts to execute following commands (not weighting for the answer). Client sends the request and weights for the answer. As soon as the answer is obtained, the client application continues to execute following commands. The second case seems to be more realistic and logical for me. However, I do not understand what happens if the server does not open a socket and it does not say that it does not "want" to open the second (it can happen if the server does not exist or network is broken). What will happen in this case? Will server weight forever? In general it would be nice for the client to know what is the result of its request for the socket. For example I can imagine the following situations: The socket is opened by the server. The server refuses to open a socket. So, server exists, it got the request from the client but it says "no". There is no response from the server. I know that new Socket(serverIP,serverPort) does not "return" this kind of information. But it throws exceptions. One of them is "UnkownHostException". When it is thrown? When the server is not responding for a while (for how long)? ADDED: I just found out that UnknownHostException is thrown to indicate that the IP address of a host could not be determined. So, it is unrelated with the above described situations (server is not responding, server refuses to open a socket).

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• NOT replacing ? with letter guessed

  - by user3720541

  i need my code to replace the ? with the letter guessed. The ? needs to be replaced with a for only those to spots. The word in array is parameter. public static void replace(String[] wordOne, String blanks, char guess) { int i; blanks = wordOne[0]; for (i = 0; i < wordOne.length; i++) { for (int j = 0; j < wordOne[0].length(); j++) { blanks = blanks.replace(blanks.charAt(j), '?'); if (wordOne[0].charAt(i) == guess) { blanks = blanks.replace(blanks.charAt(i), guess); } } } System.out.println(blanks); } }

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• problem with "select new Object ... join ... where"

  - by jacob

  Hi, I'm having a problem with an HQL query Three classes ClassOne is my BusinessObject public class ClassOne { private int id; private int status; private Set<ClassTwo> classTwos; + other fields/getters/setters/constructor etc } ClassTwo is referenced in a set of ClassOne and is kind of the history of an object of ClassOne public class ClassTwo { private int id; private int oldStatus; private int newStatus; private String message; //+ getters/setters/constructor etc } ClassThree is my DTO/VO with just one classTwo (not the whole history) public class ClassThree { private int id; private int status; private ClassTwo classTwo; public ClassThree(int pId, int pStatus, ClassTwo pClassTwo) { id=pId; status=pStatus; classTwo=pClassTwo; } //+ getters/setters etc } Now I'd like to create an HQL query like this: I'd like to get all objects of ClassThree with a certain status and if it exists the newest ClassTwo with a certain newStatus. For example: I'd like to get all the DTOs (ClassThree) of ClassOne whose status is now 1, but earlier in their history it has been 2 and I'd like to have the latest ClassTwo object which has 2 as newStatus. SELECT new ClassThree(c1.id, c1.status, c2) FROM ClassOne c1 LEFT JOIN c1.classtwos c2 (...) and (...) is where I don't know what to do, I'm not even sure if it's a join / join fetch Looked around and tried quite a lot already, but no clue. Especially with the join fetch I get some Hibernate errors like org.hibernate.QueryException: query specified join fetching, but the owner of the fetched association was not present in the select list. Fetching the BusinessObject like that is no problem SELECT distinct(c1) FROM ClassOne c1 LEFT OUTER JOIN FETCH c1.classtwos c2 and I get the ClassTwos as my field. Thanks in advance, Jacob P.S.: One thing might be important, ClassTwo has no reference to ClassOne!!

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• Update rich:dataTable binding on Ajax selectionchange

  - by MilkJug

  I want to find the current selection of the data table whenever a selection changes. I can update other items using: <a4j:ajax render=":tmp,:tmp2" event="selectionchange"> But I cannot find the current selection - I think the major issue is that the UIExtendedDataTable backing does not get updated on the Ajax request. Is there a way to update the current selection on a selectionchange (Using RichFaces 4)?

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• Print unique ascii characters in eclipse console

  - by Shaded

  Hey guys, Kind of a strange question but... here it goes. Recently my application threw an IOException that the text only had a clubs symbol in it (like the suit in cards) I know this is probably because there was a number in there that was cast to a char and printed to the screen, and I've found where that might have happened. The only problem is, I can't recreate it in eclipse because the eclipse console doesn't want to print those characters for me. All I get are boxes. I figure this is an encoding issue or something but I need eclipse to print out those characters just like the windows console would. Is there a setting I can change to do this?

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• Latex + Source Code Import

  - by KP65

  Hi guys, I'm using latex to write a program listing of all my code and am following this: http://texblog.wordpress.com/2008/04/02/include-source-code-in-latex-with-listings/ It works, but my code runs of the side of the page. How can i fix this? Thanks

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• How to handle injecting dependencies into rich domain models?

  - by Arne

  In a web server project with a rich domain model (application logic is in the model, not in the services) how do you handle injecting the dependencies into the model objects? What are your experiences? Do you use some form of AOP? Like Springs @Configurable annotation? Load time or build time weawing? Problems you encountered? Do you use manual injection? Then how do you handle different instantiation scenarios (creating of the objects through an library [like Hibernate], creating objects with "new" ...)? Or do you use some other way of injecting the dependencies?

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• Configure multiple keystores in JBoss depending on requested hostname

  - by Mo

  Hello, I have my J2EE application deployed into a JBossAS. My Application has to respond to two different hostnames (https://foo.com/myApp and https://bar.com/myApp). It is the same instance of the app serving those two hostnames. But I don't know how to configure the keystores. I need different keystores for each hostname. Is there a way to tie a virtual host in JBoss' server.xml to a specific connector? Or do I have to use two different IP-addresses and create a connector for each? A solution that does not require a second IP-address would be greatly appreciated.

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• Extract elements from list based on object property type

  - by Dustin Digmann

  Often, I have a list of objects. Each object has properties. I want to extract a subset of the list where a specific property has a predefined value. Example: I have a list of User objects. A User has a homeTown. I want to extract all users from my list with "Springfield" as their homeTown. I normally see this accomplished as follows: List users = getTheUsers(); List returnList = new ArrayList(); for (User user: users) { if ("springfield".equalsIgnoreCase(user.getHomeTown()) returnList.add(user); } I am not particularly satisfied with this solution. Yes, it works, but it seems so slow. There must be a non-linear solution. Suggestions?

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• why interface variables are static and final by default?

  - by Jothi

  why interface variables are static and final by default?

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• Who to convert a non serializable object to byte array?

  - by Tom Brito

  Who to convert a non serializable object to byte array?

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• "Overriding" instance variables in subtype: Possible risks?

  - by sebastiangeiger

  Say I had a class SuperClass and two subclasses SubClassA and SubClassB that inherit from SuperClass. abstract class SuperClass{ ... List someList; ... } class SubClassA extends SuperClass{ ... List<String> someList; ... } class SubClassB extends SuperClass{ ... List<Integer> someList; ... } That way it is convenient because I can get someList.size() in Superclass and have Typesafety in the Subclasses. The problem is that it does not "feel" right, can you think of potential hazards this apporach has that I am not aware of?

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