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  • Java template classes using generator or similar?

    - by Hugh Perkins
    Is there some library or generator that I can use to generate multiple templated java classes from a single template? Obviously Java does have a generics implementation itself, but since it uses type-erasure, there are lots of situations where it is less than adequate. For example, if I want to make a self-growing array like this: class EasyArray { T[] backingarray; } (where T is a primitive type), then this isn't possible. This is true for anything which needs an array, for example high-performance templated matrix and vector classes. It should probably be possible to write a code generator which takes a templated class and generates multiple instantiations, for different types, eg for 'double' and 'float' and 'int' and 'String'. Is there something that already exists that does this? Edit: note that using an array of Object is not what I'm looking for, since it's no longer an array of primitives. An array of primitives is very fast, and uses only as much space a sizeof(primitive) * length-of-array. An array of object is an array of pointers/references, that points to Double objects, or similar, which could be scattered all over the place in memory, require garbage collection, allocation, and imply a double-indirection for access. Edit2: good god, voted down for asking for something that probably doesn't currently exist, but is technically possible and feasible? Does that mean that people looking for ways to improve things have already left the java community? Edit3: Here is code to show the difference in performance between primitive and boxed arrays: int N = 10*1000*1000; double[]primArray = new double[N]; for( int i = 0; i < N; i++ ) { primArray[i] = 123.0; } Object[] objArray = new Double[N]; for( int i = 0; i < N; i++ ) { objArray[i] = 123.0; } tic(); primArray = new double[N]; for( int i = 0; i < N; i++ ) { primArray[i] = 123.0; } toc(); tic(); objArray = new Double[N]; for( int i = 0; i < N; i++ ) { objArray[i] = 123.0; } toc(); Results: double[] array: 148 ms Double[] array: 4614 ms Not even close!

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  • Equivalent for Java's System.getProperty("java.io.tmpdir") in C ?

    - by B_
    As the title says, the java.io.tmpdir property in Java is really nice, and I can't find an equivalent for C. I'm writing for Windows and in Visual Studio. I don't want to just use something like C:\Temp because in later versions of windows the appropriate directory could be something like C:\Users\[UserName]\AppData\Local\Temp and a way to retrieve this would be much easier. I want a directory and not just a temp file because I'm downloading and executing a file from the internet. As a side note, if anyone can give me tips about how to better google for C stuff it would be much appreciated :)

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  • Casting Class into String and Vice Versa in JAVA

    - by topgun_ivard
    I have a program in which I need to store a Class object into memory by casting it into String. Is it possible to convert the String back into the original Class so that I can use that class variables? I am doing this in JAVA. Example: test.java class hello{ public String h1; public String h2; } public class test { public static void main(String[] args) { hello h = new hello(); h.h1 = "hello"; h.h2 = "world"; String s = h.toString(); System.out.println("Print s : "+s); // Now I need to convert String s into type hello so that // I can do this: // (hello)s.h1; // (hello)s.h2; } } NOTE: this is not a homework, this is a personal project and I would be grateful if anyone can help! Thanks! Ivar

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  • Storing a big xml string in a xml document in java

    - by shyam R
    Hi All, I Have a Java object which I am converting into a xml file. I am getting a big xml file here after converting java object. I am capturing that converted xml file in a string like below String ouputXML = xmlfile; Noe If I pring the ouputXML on the console of IBM RSA in the proper format only it is printing but my requirement is I need to redirect outputXML in to an XML instead of printing in IBm RSA console. I am able to do this but the problem is if I open the craetd XML file the xml structure is not proper , it is showing so many special characters . Please help me !!

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  • Java - Loading dlls by a relative path and hide them inside a jar

    - by supertreta
    Hi guys, I am developing a Java application that should be release as a jar. This program depends on c++ external libraries called by JNI. To load them, I use the method System.load with an absolute path and this works fine. However, I really want to "hide" them inside the jar, so I have created a package to collect them. This forces me to load an relative path - the package path. By this approach, I let the user run the jar in any directory, without being worried about linking the dll's or bored with a previous installation process. This throws the expected exception: Exception in thread "main" java.lang.UnsatisfiedLinkError: Expecting an absolute path of the library How can I get this working? Thanks for your help!

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  • Java: global values inside a class?

    - by HH
    I want less methods. I want a common global TestClass from which I could use any of its value inside the class. import java.util.*; import java.io.*; public class TestClass { TestClass(String hello){ String hallo = hello; String halloSecond = "Saluto!"; } public static void main(String[] args) { TestClass test = new TestClass("Tjena!"); System.out.println("I want "Tjena!": " + test.hallo); TestClass testSecond = new TestClass("1"); System.out.println("I want Saluto!:" + test.halloSecond); System.out.println("I want Saluto!:" + testSecond.halloSecond); } }

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  • how to run the dependecy class file in java

    - by Manu
    I have created Excel Sheet using java program.It works fine. My problem is, i have copied the .class file into other directory with the necessary jar files need to create this excel sheet, for example my .class is inside "pack" package. c:/myprogram/pack/excelprogram.class to d:/myprogram /pack/excelprogram.class /jxl.jar /ojdbc14.jar if i run the program javac pack.excelprogram it display below error Caused by: java.lang.ClassNotFoundException: jxl.format.CellFormat i have dependency jar file(jxl.jar) for this excel sheet creation.Error is displaying from that only. i have set class path for this jar file like set classpath="%classpath%";d:/myprogram/jxl.jar;d:/myprogram/ojdbc14.jar;.; even though i'm getting the same error. Please help ASAP.

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  • Java date processing

    - by Don
    Hi, Given an instance of java.util.Date which is a Sunday. If there are 4 Sundays in the month in question, I need to figure out whether the chosen date is 1st Sunday of month 2nd Sunday of month 2nd last Sunday of month Last Sunday of month If there are 5 Sundays in the month in question, then I need to figure out whether the chosen date is 1st Sunday of month 2nd Sunday of month 3rd Sunday of month 2nd last Sunday of month Last Sunday of month I've had a look in JodaTime, but haven't found the relevant functionality there yet. The project is actually a Groovy project, so I could use either Java or Groovy to solve this. Thanks, Donal

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  • flipping 2d components in java

    - by aniket
    i am trying to flip a pentahex (5 hexagons joined at their sides). Is it possible to do so in Java? I mean suppose 2 of the 3 hexagons are in one quadrant can I change their quadrant? It is similar to what we do to flip images in Paint. The same utility I am trying to perform in Java. I have heard about Affine transform wherein it makes use of a bit called TYPE_FLIP, but I am not sure how to use it. Any small example would be of great help. Note: I do not want to flip images, but actual 2D objects.

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  • calling database driver in java app [basically a swing app]

    - by user993250
    I have made a java application that allows a user to choose from certain standards and then allows him to customize those standards according to his needs. Now, the customization [via a swing application] that has been made needs to be persistent. For this we use a database [mysql/access] and hook it to the application so that with each customization made, a table [if non-existent] is created [thus making it runtime and we can not pre-determine the table names or the keys of table etc] and an appropriate entry in the table is made. I have written the driver for this connection. How do I call it in the java application and what approach should I take? I would much appreciate that if somebody can refer me some example that not only shows a sample connection being made via driver but its appropriate calls to the database as well so that i can use it as a guide.

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  • Instantiating Java object with a passed in method

    - by superluminary
    It's been a few years since I've been heavily into Java. Coming back to it I'm seeing this pattern all over the place: ratingBar.setOnRatingBarChangeListener(new OnRatingBarChangeListener() { public void onRatingChanged(RatingBar ratingBar, float rating, boolean fromUser) { // do work } }); This looks more like Functional programming to me. It's a nice pattern but how is it possible to pass a method like this? In the old days a class was a class, and once compiled there was little you could do to it. My questions are: Can anyone let me know what this pattern is called? How can I write a class that can be instantiated in this way. Are there any other useful examples of functional patterns that have made their way into Java? What do I need to Google to read more about this? Thanks.

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  • What is the Fastest Java/PHP Bridge?

    - by The Rook
    A bi-directional communication is required between a Java application and a PHP web app. A Fast and low Resource consumption is the number 1 priority in this project There is the PHP/Java Brdige(PJB) project and there are benchmarks to show that is very fast. Do you know of a faster approach? xml over http strikes me as a bit wasteful, but I don't know of a better approach. Ideally this system would be a remote connection, but due to time constraints it might have to be local. Do you know of a fastest way to accomplish this bi-directional connection?

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  • New to JEE; architecture suggestions for a service/daemon?

    - by Kate
    I am brand new to the JEE world. As an exercise to try and familiarize myself with JEE, I'm trying to create a tiered web-app, but I'm getting a little stuck on what the best way is to spin up a service in the background that does work. Parameters of the service: It must open and hold a socket connection and receive information from the connected server. There is a 1-to-1 correlation between a user and a new socket connection. So the idea is the user presses a button on the web-page, and somewhere on the server a socket connection is opened. For the remainder of the users session (or until the user presses some sort of disconnect button) the socket remains open and pushes received information to some sort of centralized store that servlets can query and return to the user via AJAX. Is there a JEE type way to handle this situation? Naturally what I would think to do is to just write a Java application that listens on a port that the servlets can connect to and spawns new threads that open these sockets, but that seems very ad-hoc to me. (PS: I am also new to Stack Overflow, so forgive me if it takes me some time to figure the site out!)

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  • Quick to develop web app in Java

    - by Mike Q
    Hi all, I need to develop a basic web app very quickly (1 week) for a demo. My requirements are Java (I need to make use of existing Java libraries to access the relevant data) 2 screens One for static data view, maybe some search parameters Other for basic form entry No fancy AJAX required Ideally easy for a web designer to come in and tart it up as necessary, without having to rewrite everything My first stop was going to be to checkout Wicket as I've heard good things about it. I don't have the time right now to dive into anything heavy, which probably writes off JSF in my mind (I played with JSF1, steep learning curve which I've now slid back down). I'm happy to treat the result as throwaway so if there's a framework which starts of well but then doesn't scale up to bigger projects, that would be ok. Any suggestions appreciated on frameworks/approach.

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  • Converting a C++ Checksum function to Java

    - by user1897599
    I'm trying to convert this C++ checksum to Java but for the time being I've failed. What am I doing wrong? What is it supposed to do? It is supposed to return a positive checksum for a buffer in OpenGL Here's the C part. DWORD QuickChecksum(DWORD *data, int size){ if(!data) { return 0x0; } DWORD sum; DWORD tmp; sum = *data; for(int i = 1; i < (size/4); i++) { tmp = data[i]; tmp = (DWORD)(sum >> 29) + tmp; tmp = (DWORD)(sum >> 17) + tmp; sum = (DWORD)(sum << 3) ^ tmp; } return sum; } And here is what I have tried in Java. As far As I know DWORD is 32bit so I use int in a long to get a unsigned int which should be done in java with ? I've been looking at this problem so much now that I've grown blind to it. public static long getChecksum(byte[] data, int size) { long sum, tmp; sum = getInt(new byte[]{data[0], data[1], data[2], data[3]},true) & 0xFF; for(int I = 4; I < data.length; I += 4) { tmp = getInt(new byte[]{data[I],data[I+1],data[I+2],data[I+3]},true) & 0xFF; tmp = (sum >>> 29) + tmp; tmp = (sum >>> 17) + tmp; sum = (sum << 3) ^ tmp; } return sum & 0xFF; } private static int getInt(byte[] bytes, boolean big) { ByteBuffer bb = ByteBuffer.wrap(bytes); return bb.getInt(); } Thank you all for your help!

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  • java: communication between threads

    - by TRU7H
    I'm making a little java game in which I would have two threads (well as the FIRST step towards multithreading...), one for the logic and one for the drawing. So my question is: How can I make those two communicating which each other? Requirements: accessing variables and object from a another thread syncing them so they each complete a same number of "loops" in the same time. (the logic calculates and then the another one draws the results and the loop begins again...) So how is this achievable in java? Thanks in advance!

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  • Have an external java application by notified of changes to Entity EJBs in JBoss AS

    - by John
    I'm trying to connect an external application to a JBoss AS container. The external application is a Java application that is currently being notified of changes to database entities through a JMS topic. I've added an EntityLifecycleListener class to all my entities that publishes a serialized (and unwrapped) copy of the entity to the JMS topic. The problem is that this implementation ignores the transaction boundaries of the JBoss container. For example, the @PostUpdate event can be fire, generating the JMS message for that entity, but the transaction could be rolled back causing the external application to be notified of an invalid change and become unsync'd. I need my external application to only be notified of successful commits to the database, but I need to be able to publish the entire java POJO to the external application. Is there an official way of doing this?

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  • How do I cast from int to generic type Integer?

    - by Rob Kent
    I'm relatively new to Java and am used to generics in C# so have struggled a bit with this code. Basically I want a generic method for getting a stored Android preference by key and this code, albeit ugly, works for a Boolean but not an Integer, when it blows up with a ClassCastException. Can anyone tell me why this is wrong and maybe help me improve the whole routine (using wildcards?)? public static <T> T getPreference(Class<T> argType, String prefKey, T defaultValue, SharedPreferences sharedPreferences) { ... try { if (argType == Boolean.class) { Boolean def = (Boolean) defaultValue; return argType.cast(sharedPreferences.getBoolean(prefKey, def)); } else if (argType == Integer.class) { Integer def = (Integer) defaultValue; return argType.cast(sharedPreferences.getInt(prefKey, def)); } else { AppGlobal.logWarning("getPreference: Unknown type '%s' for preference '%s'. Returning default value.", argType.getName(), prefKey); return defaultValue; } } catch (ClassCastException e) { AppGlobal.logError("Cast exception when reading pref %s. Using default value.", prefKey); return defaultValue; } } I've tried various ways - using the native int, casting to an Integer, but nothing works.

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