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• In Java how does one turn a String into a char or a char into a String?

  - by David

  Is there a way to turn a char into a String or a String with one letter into a char (like how you can turn an int into a double and a double into an int)? (please link to the relevant documentation if you can). How do I go about finding something like this that I'm only vaguely aware of in the documentation?

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• Multithreaded java cache for objects that are heavy to create ?

  - by krosenvold

  I need a cache some objects with fairly heavy creation times, and I need exactly-once creation semantics. It should be possible to create objects for different CacheKeys concurrently. I think I need something that (under the hood) does something like this: ConcurrentHashMap<CacheKey, Future<HeavyObject>> Are there any existing open-source implementations of this that I can re-use ?

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• Java Persistence: Cast to something the result of Query.getResultList() ?

  - by GuiSim

  Hey everyone, I'm new to persistence / hibernate and I need your help. Here's the situation. I have a table that contains some stuff. Let's call them Persons. I'd like to get all the entries from the database that are in that table. I have a Person class that is a simple POJO with a property for each column in the table (name, age,..) Here's what I have : Query lQuery = myEntityManager.createQuery("from Person") List<Person> personList = lQuery.getResultList(); However, I get a warning saying that this is an unchecked conversion from List to List<Person> I thought that simply changing the code to Query lQuery = myEntityManager.createQuery("from Person") List<Person> personList = (List<Person>)lQuery.getResultList(); would work.. but it doesn't. Is there a way to do this ? Does persistence allow me to set the return type of the query ? (Through generics maybe ? )

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• best way in java to rename a file , there are about 500 files in a directory.

  - by Suresh S

  I have 500 pdf files in a directory. i want to remove first five character of a filename and rename it. please let me know your comments.

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• How can two programs talk to each other in Java?

  - by Arnon

  I want to ?reduce? the CPU usage/ROM usage/RAM usage - generally?, all system resources that my app uses - who doesn't? :) For this reason I want to split the preferences window from the rest of the application, and let the preferences window to run as ?independent? program. The preferences program ?should? write to a Property file(not a problem at all) and to send a "update signal" to the main program - which means it should call the update method (that i wrote) that found in the Main class. How can I call the update method in the Main program from the preferences program? To put it another way, is a way to build preferences window that take system resources just when the window appears? Is this approach - of separating programs and let them talk to each other (somehow) - the right approach for speeding up my programs?

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• Is there any possibility to add a outlook calendar (.ics) file to the google calendar form java.

  - by Alex

  i need add a calendar file to google calendar from my code. Is it possible to add a calendar file directly to the google calendar?

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• Why do methods contains(), indexOf() in a Java Collection use o.equals(e) and not e.equals(o)?

  - by Fernando

  anyone know the reasons of that??

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• can I rotate the button or label into vertically in java?

  - by Venkats

  I want button in vertically, for that i can extend the height and shrink the width of that button. But the text of the lable of buttons are in the form of horizontal only. For that can i rotate the whole button vertically and is it possible?

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• Is there some tool to visualize Java class hierarchies and relations?

  - by Niyaz

  Here is my problem: I will provide the source code of my application as input and what I want as output is a visual representation of the relationship between classes, method calls etc. Is there some tool to do this?

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• Java: how can I split an ArrayList in multiple small ArrayLists ?

  - by Patrick

  hi, how can split an ArrayList (size=1000) in multiple ArrayLists of the same size (=10) ? ArrayList results; Thanks

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• How come JFrame window size in Java does not produce the size of window specified?

  - by typoknig

  Hi all, I am just messing around trying to make a game right now, but I have had this problem before too. When I specify a specific window size (1024 x 768 for instance) the window produced is just a little larger than what I specified. Very annoying. Is there a reason for this? How do I correct it so the window created is actually the size I want instead of being just a little bit bigger? Up till now I have always just gone back and manually adjusted the size a few pixels at a time until I got the result I wanted, but that is getting old. If there was even a formula I could use that would tell me how many pixels I needed to add/subtract from my my variable that would be excellent! P.S. I don't know if my OS could be a factor in this, but I am using W7X64. private int windowWidth = 1024; private int windowHeight = 768; public SomeWindow() { this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); this.setSize(windowWidth, windowHeight); this.setResizable(false); this.setLocation(0,0); this.setVisible(true); }

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• Java, How to Instance HttpCookie from a String, any convenient ways?

  - by user435657

  Hi all, I have got a cookie string from HTTP response header like the following line: name=value; path=/; domain=.g.cn; expire=... I can parse the above line to key-value pairs, and, also it's easy to set the name and value to HttpCookie instance as this pair comes the first. But how to set the other pairs since I don't know which set-method corresponds to the name of the next name-value pair. Traverse all possible keys a cookie may contian and call the matched set-method, like below snippet? if (key.equalsIgnoreCase("path")) cookie.setPath(value); else if (key.equalsIgnoreCase("domain")) cookie.setDomain(value); That's foolish, any convenient ways? Thanks in advance.

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• Java JIT compiler compiles at compile time or runtime ?

  - by Tony

  From wiki: In computing, just-in-time compilation (JIT), also known as dynamic translation, is a technique for improving the runtime performance of a computer program. So I guess JVM has another compiler, not javac, that only compiles bytecode to machine code at runtime, while javac compiles sources to bytecode,is that right?

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• Why Java compiler does not like integer as type for values in HashMap?

  - by Roman

  The compiler complains about this code: HashMap<String,int> userName2ind = new HashMap<String,int>(); for (int i=0; i<=players.length; i++) { userName2ind.put(orderedUserNames[i],i+1); } It writes "unexpected type" and point on int. If I replace int by String and i+1 by i+"1", the compilation goes OK. What is wrong with in here?

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• Java: most efficient way to defensively copy an int[]?

  - by Jason S

  I have an interface DataSeries with a method int[] getRawData(); For various reasons (primarily because I'm using this with MATLAB, and MATLAB handles int[] well) I need to return an array rather than a List. I don't want my implementing classes to return the int[] array because it is mutable. What is the most efficient way to copy an int[] array (sizes in the 1000-1000000 length range) ? Is it clone()?

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• Is there an easy way to copy an iterator into a list in Java?

  - by Space_C0wb0y

  I want something like this: public void CopyIteratorIntoList(Iterator<Foo> fooIterator) { List<Foo> fooList = new ArrayList<Foo>(); fooList.addAll(fooIterator); } which should be equivalent to: public void CopyIteratorIntoList(Iterator<Foo> fooIterator) { List<Foo> fooList = new ArrayList<Foo>(); while(fooIterator.hasNext()) fooList.add(fooIterator.next()); } Is there any method in the API to achieve that, or is this the only way?

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• Java. Writing a matrix in a file using column information. ( matrix transposition )

  - by Dmitry

  Hello, everybody! I have a file in which a matrix is stored. This file has a RandomAccessFile type. This matrix is stored by columns. I mean that in an i-th row of this matrix an i-th column (of a real matrix) is stored. There is an example: i-th row: 1 2 3 4 (in the file). That means that the real matrix has an i-th column: (1 2 3 4)(is transposed). I need to save this matrix in a natural way (by rows) in a new file, which I will then open with FileReader and display with TextArea. Do you know, how to do that? If so, please help =)

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• Java - Is it possible to override an ActionListener in the SuperClass?

  - by KP65

  If have two classes, Class A and Class B, B is a subclass of A...if my Class A(the superclass) has a JButton with an ActionListener which is implemented by an anonymous inner class, how can I override what the button does in the subclass?

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• How to construct a relative path in Java from two absolute paths (or URLs)?

  - by VoidPointer

  Given two absolue paths, e.g. /var/data/stuff/xyz.dat /var/data How can one create a relative path that uses the second path as its base? In the example above, the result should be: ./stuff/xyz.dat

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• Remove successive 0th entries in args[] for a Java command line interface?

  - by Bill IV

  I recall seeing, somewhere, an example that stepped through String args[] by deleting the lowest numbered value(s) public static void main( String args[]) { while (args.length > 0 ) { // do something and obliterate elements from args[] } } Obviously, a variable tracking current position in args and compared to args.length will do it; or an ArrayList made from args[]'s contents, with argsAL.size(). Am I mis-remembering an ArrayList example? I know this is a borderline question, the likely answer is, "No, there isn't and there shouldn't be either!". Maybe I'm over-focused... Bill

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• Why am I getting a Java NoSuchPortException when the port exists?

  - by user258526

  Got the following production code below, I'm using it for a new driver. portName is COM4 and this port exists on the PC (and I can connect to it with hyperterminal), so why does Javacomm throw a NoSuchPortException? COM4 shows up fine in device mgr. too final String portName = getSerialPort(); try { final CommPortIdentifier id = CommPortIdentifier.getPortIdentifier(portName); port = (SerialPort) id.open(getName(), 1000); } catch (NoSuchPortException nspe) { report(SeverityCode.LEVEL2, getName(), "PIN Pad is not connected to " + portName + " port, or the port does not exist."); return; } catch (PortInUseException piue) { report(SeverityCode.LEVEL2, getName(), portName + " port is already in-use by some other device. Reason: " + piue.getMessage()); return; }

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• Fastest and most efficent way of seaching a key-value pair in Java?

  - by Mohit Deshpande

  DISCLAIMER: THIS QUESTION WAS NOT MENT TO BE ARGUMENTATIVE!!!!!!! What is fastest and less memory draining way of searching a key-value pair? I will be storing items in a key-value like relation and I need to access them quickly. Should I use a SQLite database? A Map? A Hashtable? A HashMap? Please give some advantages/disadvantages of using whatever method of searching.

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• How to set session timeout dinamically in java web applications?

  - by Jonathas Carrijo

  Hi, I need to give my user a web interface to change the session timeout interval. So, each installation of the application might have different timeouts for their sessions, but they web.xml cannot be different. Is there a way to set the session timeout programatically, so that I could use, say, ServletContextListener.contextInitialized() to read the configured interval and set it upon application startup? Thanks a lot.

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• Convert bit vector (array of booleans) to an integer, and integer to bit vector, in Java.

  - by dreeves

  What's the best way to unstub the following functions? // Convert a bit-vector to an integer. int bitvec2int(boolean[] b) { [CODE HERE] } // Convert an integer x to an n-element bit-vector. boolean[] int2bitvec(int x, int n) { [CODE HERE] } Or is there a better way to do that sort of thing than passing boolean arrays around? This comes up in an Android app where we need an array of 20 booleans to persist and the easiest way to do that is to write an integer or string to the key-value store. I'll post the way we (Bee and I) wrote the above as an answer. Thanks!

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• Pass the return type as a parameter in java?

  - by jonderry

  I have some files that contain logs of objects. Each file can store objects of a different type, but a single file is homogeneous -- it only stores objects of a single type. I would like to write a method that returns an array of these objects, and have the array be of a specified type (the type of objects in a file is known and can be passed as a parameter). Roughly, what I want is something like the following: public static <T> T[] parseLog(File log, Class<T> cls) throws Exception { ArrayList<T> objList = new ArrayList<T>(); FileInputStream fis = new FileInputStream(log); ObjectInputStream in = new ObjectInputStream(fis); try { Object obj; while (!((obj = in.readObject()) instanceof EOFObject)) { T tobj = (T) obj; objList.add(tobj); } } finally { in.close(); } return objList.toArray(new T[0]); } The above code doesn't compile (there's an error on the return statement, and a warning on the cast), but it should give you the idea of what I'm trying to do. Any suggestions for the best way to do this?

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