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• How is a constructor executed?

  - by simion

  I am doing some reviison from the lecture slides and it says a constructor is executed in the following way; If the constructor starts with this, recursively execute the indicated constructor, then go to step 4. Invoke the explicitly or implicitly indicated superclass constructor (unless this class is java.lang.Object) Initialise the fields of the object in the order in which they were declared in this class Execute the rest of the body of this constructor. What i dont undertsand is that, a constructor can never "start" with this, because even if it forms no class heirarchy/relationship then super() is inserted by default. How would this fit in with the description above? Thanks

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• Strings - Filling In Leading Zeros Wtih A Zero

  - by headscratch

  I'm reading an array of hard-coded strings of numeric characters - all positions are filled with a character, even for the leading zeros. Thus, can confidently parse it using substring(start, end) to convert to numeric. Example: "0123 0456 0789" However, a string coming from a database does not fill in the leading zero with a 'zero character', it simply fetches the '123 456 789', which is correct for an arithmetic number but not for my needs and makes for parsing trouble. Before writing conditionals to check for leading zeros and adding them to the string if needed, is there a simple way of specifying they be filled with a character ? I'm not finding this in my Java book... I could have done the three conditionals in the time it took to post this but, this is more about 'education'... Thanks

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• Hibernate + Spring + session + cache

  - by andromeda

  We are using Hibernate with Spring for our Java application. We find out that when a session update something in database other sessions can not see the update. For example user1 get the account balance from database then user2 increase the balance , if user1 get the object another time he see the account balance before updating (seems that session use the value from its cache) but we want to get the updated object with new account balance. User1 use one session during all activity that is different from user2 session. Is any configuration to force to get the updated object from database? or any other help?

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• Programatically convert complex Excel file into HTML format

  - by shuby_rocks

  Hello all, I have a set of complex Excel files (with figures in it) that I want to show in a web browser. So I need to convert them into HTML page first. Since the excel files are very complex, I can not just parse them and generate a HTML table with HTML tags. The current manual solution that works fine is when I use Microsoft Excel software to save the spreadsheet as a HTML page. I want to automate this task in some way since I want to do it progrmatically through Java. Is their any existing solution or a way to do it? Thanks.

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• Reduce text length to fit cell width in a smart manner

  - by Andrei Ciobanu

  Hello, I am in project where we are building a simple web calendar using Java EE technologies. We define a table where every row is an employee, and every column represents an hour interval. The table width and column widths are adjustable. In every cell we have a text retrieved from a database, indicating what the employee is doing / should do in that time interval. The problem is that sometimes the text in cells is getting bigger than the actual cell. My task is to make the text more "readable" by reducing it's length in a "smart way" so that it can fit in the cell more "gracefully". For example if initially in a cell I have: "Writing documents", after the resize I should retrieve: "Wrtng. dcmnts" or "Writ. docum." so that the text can fit well. Is there a smart way to do it ? Or removing vocals / split the string in two is enough ?

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• Do fields need to be explicitly final to have a "proper" immutable object?

  - by Yishai

  You often read about immutable objects requiring final fields to be immutable in Java. Is this in fact the case, or is it simply enough to have no public mutability and not actually mutate the state? For example, if you have an immutable object built by the builder pattern, you could do it by having the builder assign the individual fields as it builds, or having the builder hold the fields itself and ultimately return the immutable object by passing the values to its (private) constructor. Having the fields final has the obvious advantage of preventing implementation errors (such as allowing code to retain a reference to the builder and "building" the object multiple times while in fact mutating an existing object), but having the Builder store its data inside the object as it is built would seem to be DRYer. So the question is: Assuming the Builder does not leak the Object early and stops itself from modifying the object once built (say by setting its reference to the object as null) is there actually anything gained (such as improved thread safety) in the "immutability" of the object if the object's fields were made final instead?

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• Accessing and encoding of properties files

  - by NoozNooz42

  I'm used to work with properties files, for example from Ant. Where I can simply reference the property file doing something like that: <property file="webapp_DO_NOT_COMMIT.properties"/> (the file is so named because our DVCS is configured as to never commit files containing "DO_NOT_COMMIT" to prevent committing credentials/passwords/etc.) Here's a very simple .properties file example: passwd=brokencleartextpassword Now I want to put some configuration in another, similar, properties file that I need to access from my Java code. How should I go about it? I also have another related question: is the character encoding of .properties file defined by any spec?

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• Inferring type from method generics

  - by ng

  I am from a Java background and I am looking from the equivalent in c# for the following. public interface Reader { <T> T read(Class<? extends T> type); } Such that I can do the following, constraining the parameter and inferring the return type. Cat cat = reader.read(Cat.class); Dog dog = reader.read(Dog.class); I was hoping something like this would work in c# but I am not sure it will. public interface Reader { T Read<T>(); } And and do this. public class TypeReader : Reader { public T Read<T>() { Type type = T.GetType(); ... } } Is something like this even possible in c#?

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• String as \x03\x00\x00\x00 to integer

  - by marta

  Helo: I have a question, that I solved in c, but now I want to do it in hava: I have a String like: '\x03\x00\x00\x00' This is representing an hexadecimal value of a integer. I transform to 0x03\0x00... And now I want to obtain the integer, but I don't know how to do it in java could someone give me some idea ? Thanks in advance (Is it some way to use this format ('\x03\x00\x00\x00' ) directly without use byte[] arrays? and in C can I use this format directly to build a integer (int)?)

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• NullPointerException when accessing image files in a .jar file

  - by user548240

  Hi, I have pretty much tried everything but still have this same problem. I have the following setup: I have a images.jar containing a folder called 'images' in which there are multiple image files. I add images.jar to the java build path of the project in eclipse, and i've been trying to use the following code to access the individual images in the jar: URL url = this.getClass().getResource("images/a.png"); ImageIcon icon = new ImageIcon (url); Unfortunately, the URL object is always NULL. I don't think this has anything to do with where I put images.jar file as it is added to the classpath in eclipse. I have also tried using the path '/images/a.png', but still the same problem. Any suggestion would be extremely welcome! Thanks.

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• how to achieve Inter-Widget communication

  - by bakore

  I was looking for a platform where widgets developed using various technologies like Java can communicate with each other. In other words When I add widgets to an interface I need them to talk to each other. For example A Click event in one widget should trigger an event in some other widget. I have been looking into the web for solutions and ways to do it, but couldnt find anything concrete. Any pointers or information on this would be great. Something like this http://blogs.sun.com/pdblog/entry/inter_widget_communication_in_cross

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• Eclipse bug? Switching on a null with only default case

  - by polygenelubricants

  I was experimenting with enum, and I found that the following compiles and runs fine on Eclipse (Build id: 20090920-1017, not sure exact compiler version): public class SwitchingOnAnull { enum X { ,; } public static void main(String[] args) { X x = null; switch(x) { default: System.out.println("Hello world!"); } } } When compiled and run with Eclipse, this prints "Hello world!" and exits normally. With the javac compiler, this throws a NullPointerException as expected. So is there a bug in Eclipse Java compiler?

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• Count The Amount Of Data In An Array Including SOME Null

  - by Josephine

  I'm coding in java and I need to create a function that returns the number of Data objects that are currently in an ArrayList. At the moment I have this: int count = 0; for (int i = 0; i < data.length; i++) { if (data[i] != null) { count ++; } } return count; But the problem is that an array list that includes null data is acceptable, and I have to count their null data towards this counter. How do I include the null data that's in the middle of this array, and not the null data that's not supposed to be counted for? For example, I have some tester code that adds (8),null,null,(23),(25) to the array, and this function should return 5 when the initial array size is 10. Thank you so much

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• Hashing and salting values

  - by Avanst

  I am developing a small web app that internally authenticates users. Once the user is authenticated my web app then passes some information such as userID and Person's name to a third party web application. The third party developer is suggesting that we hash and salt the values. Forgive my ignorance, but what exactly does that mean? I am writing the app in Java. So what I am planning on doing is hashing the userID, Person's name, and some Math.random() value as the salt with Apache Commons Digest Utils SHA512 and passing that hashed string along with the userID and person's name. Is that the standard practice? I should be passing the third party the salt as well correct?

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• What happens when a OSGi service using JNI is unregistered while in use?

  - by schngrg

  As I understand, OSGi services can be unregistered anytime, including when they are in use. Consider an OSGi service which internally makes a long-running JNI call. And while that JNI call is executing, the service is unregistered by OSGi. Will the JNI call be allowed to finish or terminated mid-way? What if it was just a normal non-jni long running Java call? Will that call be allowed to finish execution or will OSGi terminate everything immediately and unregister? What is the expected behavior in such a case? Does the expected behavior depend on if the service was loaded using a 'tracker' or not? SG

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• Send data over telnet without pressing enter

  - by Matt

  I've recently started messing around with Java sockets and telnet... I want the user to be able to connect to the server, just type a letter and have it sent to the server, without pressing enter to send it. I'm sure there's no way for the server to set this up, but maybe telnet has a parameter or something which could allow this? Maybe if I got the user to type stty cbreak or stty raw before running telnet, this would work? (UNIX only, I know!) If I can get telnet to do this then it saves me having to write a special client just for this feature...

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• How do you make long SQL invoked from other code readable?

  - by Artem

  This is a very open question, but I think it can be very beneficial for SQL readability. So you have a Java program, and you are trying to call a monster SQL statement from it, with many subqueries and joins. The starting point for my question is a string constant like this: static string MONSTER_STATEMENT = "SELECT " + " fields" + "WHERE "+ " fieldA = (SELECT a FROM TableC) " + "AND fieldB IN (%s)" + "AND fieldC = %d " + "FROM " " tableA INNER JOIN tableB ON ..."; It later gets filled using String.format and executed. What are you tricks for making this kind of stuff readable? Do you separate your inner joins. Do you indent the SQL itself inside the string? Where do you put the comments? Please share all of the tricks in your arsenal.

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• Tomcat + Struts + OpenID raising ServletExceptions

  - by Rocjoe

  I am working with Tomcat 5.5.x with Struts 1.2 to run a rather large website (large w.r.t. source code). I'm looking to add OpenID to my website, mostly to access attribute exchange to help accelerate the registration process. Every Java implementation for OpenID I have attempted to use will cause a ServletException. Tracing this has been very difficult, but it seems merely instancing any class that makes use of Apache HttpClient will cause the crash. Is this a configuration problem I can address in the JVM, or is it positively wrong to try to initiate an outbound Http request from within an inbound Http request?

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• Obtain distances to nearest landmarks (Mall, Hospital, and Airport etc.) using google map

  - by user227290

  I am working on a project in which I have around 100000 addreses in major cities in India(it is a table in a database). I want to know if it is possible to obtain the distances to to nearest landmarks (Mall, Hospital, and Airport etc.). Ideally I want these distances to be mergeed to the parent table. We have Java and Php coders to get it done once we find out how to go about it. Any pointers will be of great help. Thank you.

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• Mixing synchronized() with ReentrantLock.lock()

  - by yarvin

  In Java, do ReentrantLock.lock() and ReetrantLock.unlock() use the same locking mechanism as synchronized()? My guess is "No," but I'm hoping to be wrong. Example: Imagine that Thread 1 and Thread 2 both have access to: ReentrantLock lock = new ReentrantLock(); Thread 1 runs: synchronized (lock) { // blah } Thread 2 runs: lock.lock(); try { // blah } finally { lock.unlock(); } Assume Thread 1 reaches its part first, then Thread 2 before Thread 1 is finished: will Thread 2 wait for Thread 1 to leave the synchronized() block, or will it go ahead and run?

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• Set intersection of two strings

  - by user1785712

  import java.util.*; class set { public static void main(String args[]) { TreeSet<Character> t1 = new TreeSet<Character>(); TreeSet<Character> t2 = new TreeSet<Character>(); String s1 = "Ambitab bachan"; String s2 = "Ranjikanth"; for(char c1:s1.toCharArray()) t1.add(c1); for(char c2:s2.toCharArray()) t2.add(c2); t2.retainAll(t1); System.out.println(t2); } } this program find the common character in two different string. in this program Treeset is used to store the value and retainAll() method is used to find the common characters. can anybody help me reduce the line of coding.thanks in advance

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• Best way to access a sqlite database file in a web service.

  - by rogernorling

  First question from me on stack overflow. I have created a java web application containing a web service using netbeans (I hope a web application were the correct choice). I use the web application as is with no extra frameworks. This web service use a sqlite JDBC driver for accessing a sqlite database file. My problem is that the file path end up incorrect when I try to form the JDBC connection string. Also, the working directory is different when deploying and when running JUnit tests. I read somewhere about including the file as a resource, but examples of this were nowhere to be seen. In any case, what is the best way to open the sqlite database, both when the web service is deployed and when I test it "localy"? I don't know much about web services, I just need it to work, so please, help me with the technicalities.

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• What is the most efficient way to pass data (list of pairs of [Integer + Double]) between two Google App Engine instances?

  - by ruslan

  What is the most efficient way to pass data (list of pairs of [Integer, Double]) between two Google App Engine instances ? Currently I use Java binary serialization. Frontend servlet receives data from the client in JSON format. I convert it to byte[] using ObjectOutput.writeObject and then send it to backend servlet via HTTP POST. It's not in production yet. Should I just pass client's JSON as it is to backend? It seems more logical. But it's bigger in size. Or should I use Google Protocol Buffers as stated in this benchmark article ? Thank you!!!

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• Hibernate criterion Projection alias not being used

  - by sbzoom

  Do Hibernate Projection aliases even work? I could swear it just doesn't. At least, it doesn't do what I would expect it to do. Here is the java: return sessionFactory.getCurrentSession().createCriteria( PersonProgramActivity.class ).setProjection( Projections.projectionList().add( Projections.alias( Projections.sum( "numberOfPoints" ), "number_of_points" ) ).add( Projections.groupProperty( "person.id" ) ) ).setFirstResult( start ).setFetchSize( size ).addOrder( Order.desc( "numberOfPoints" ) ).list(); Here is the SQL that it generates: select sum(this_.number_of_points) as y0_, this_.person_id as y1_ from PERSON_PROGRAM_ACTIVITY this_ group by this_.person_id order by this_.number_of_points desc It doesn't seem to use the alias at all. I would think setting the alias would mean that "sum(this_.number_of_points)" would be aliased as "number_of_points" and not "y0_". Is there some trick I am missing? Thanks.

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• How to update mutual entries in DB?

  - by Sthita

  I am not able to perform mutual update to my Database. My Requirement is like this : Insert IDS UPDate DB Entries ID ConnectedTo ID connectedTo connectedVia 2 1 --- No Entry ----- 2 3 -- No Entry ----- When ID 1 Comes in to picture (Enties happened to Table) 1 4 1 3 2 1 5 2 4 1 1 2 2 5 1 When ID 3 Comes into picture (Enties happened to Table) 3 4 3 5 1 3 1 ---- 3 2 ---- Similarly when ID 4 Comes in to picture 4 9 4 2 3 4 10 4 5 1 4 3 4 2 1 4 1 1 9 4 1 10 4 Its basically Updating the mutual connections.No Duplicate entries should happen. Like for example 2 3 and 3 2 are mutually connected and 1 is associated with them so there is no need to insert (3 2 via 1). I think this is my requirement. Anything possible combinations i have missed please let me know. i will Update. Please help me writing the logic or any example using jdbc and java.

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