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  • Passing the Class<T> in java of a generic list?

    - by Rob Stevenson-Leggett
    I have a method for reading JSON from a service, I'm using Gson to do my serialization and have written the following method using type parameters. public T getDeserializedJSON(Class<T> aClass,String url) { Reader r = getJSONDataAsReader(url); Gson gson = new Gson(); return gson.fromJson(r, aClass); } I'm consuming json which returns just an array of a type e.g. [ { "prop":"value" } { "prop":"value" } ] I have a java class which maps to this object let's call it MyClass. However to use my method I need to do this: RestClient<ArrayList<MyClass>> restClient = new RestClient<ArrayList<MyClass>>(); ArrayList<MyClass> results = restClient.getDeserializedJSON(ArrayList<MyClass>.class, url); However, I can't figure out the syntax to do it. Passing just ArrayList.class doesn't work. So is there a way I can get rid of the Class parameter or how do I get the class of the ArrayList of MyClass?

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  • How to call a method in another class in Java?

    - by Puchatek
    Currently I have two classes. a classroom class and a School class. I would like to write a method in the School class to call public void setTeacherName(String newTeacherName) from the classroom class. public class classroom { private String classRoomName; private String teacherName; public void setClassRoomName(String newClassRoomName) { classRoomName = newClassRoomName; } public String returnClassRoomName() { return classRoomName; } public void setTeacherName(String newTeacherName) { teacherName = newTeacherName; } public String returnTeacherName() { return teacherName; } } import java.util.ArrayList; public class School { private ArrayList<classroom> classrooms; private String classRoomName; private String teacherName; public School() { classrooms = new ArrayList<classroom>(); } public void addClassRoom(classroom newClassRoom, String theClassRoomName) { classrooms.add(newClassRoom); classRoomName = theClassRoomName; } // how to write a method to add a teacher to the classroom by using the classroom parameter // and the teachers name }

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  • How to call a method in another class using the arraylist index in java?

    - by Puchatek
    Currently I have two classes. A Classroom class and a School class. public void addTeacherToClassRoom(Classroom myClassRoom, String TeacherName) I would like my method addTeacherToClassRoom to use the Classroom Arraylist index number to setTeacherName e.g. int 0 = maths int 1 = science I would like to setTeacherName "Daniel" in int 1 science. many, thanks public class Classroom { private String classRoomName; private String teacherName; public void setClassRoomName(String newClassRoomName) { classRoomName = newClassRoomName; } public String returnClassRoomName() { return classRoomName; } public void setTeacherName(String newTeacherName) { teacherName = newTeacherName; } public String returnTeacherName() { return teacherName; } } import java.util.ArrayList; public class School { private ArrayList<Classroom> classrooms; private String classRoomName; private String teacherName; public School() { classrooms = new ArrayList<Classroom>(); } public void addClassRoom(Classroom newClassRoom, String theClassRoomName) { classrooms.add(newClassRoom); classRoomName = theClassRoomName; } public void addTeacherToClassRoom(Classroom myClassRoom, String TeacherName) { myClassRoom.setTeacherName(TeacherName); } }

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  • Java: Cleaing up connection reset (but not by peer).

    - by Zombies
    There seems to be some confusion as well contradicting statements on various SO answers: http://stackoverflow.com/questions/585599/whats-causing-my-java-net-socketexception-connection-reset . You can see here that the accepted answer states that the connecteion was closed by other side. But this is not true, closing a connection doesn't cause a connection reset. It is cauesed by "an underlying TCP/IP error." What I want to know is if a SocketException: Connection reset means really besides "unerlying TCP/IP Error." What really causes this? As I doubt it has anything to do with the connection being closed (since closing a connection isn't an exception worthy flag, and reading from a closed connection is, but that isn't an "underlying TCP/IP error." My hypothesis is this Connection reset is caused from a server's failure to acknowledge an ACK packet (either wholly or just improperly as per TCP/IP). And that a SocketTimeoutException is generated only when no data is generated to be read (since this is thrown during a read after a certain duration, and read is waiting for data, but is not concerned with ACK packets). In other words, read() throws SocketTimeoutException if it didn't read any bytes of actual data (DATA LAYER) in its allotted time.

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  • How to specify hash algorithm when updating LDAP via Java?

    - by JuanZe
    Is there a way to specify the hash algorithm (MD5, SHA1, etc.) to use for storing the passwords when you update an Open LDAP directory using Java APIs with code like this: private void resetPassword(String principal, String newPassword) throws NamingException { InitialDirContext ctxAdmin = null; Hashtable<String, String> ctxData = new Hashtable<String, String>(); ctxData.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.ldap.LdapCtxFactory"); ctxData.put(Context.PROVIDER_URL, "ldap://myserver:389"); ctxData.put(Context.SECURITY_AUTHENTICATION, "simple"); ctxData.put(Context.SECURITY_PRINCIPAL, "admin_dn"); ctxData.put(Context.SECURITY_CREDENTIALS, "admin_passwd"); InitialDirContext ctxAdmin = new InitialDirContext(ctxData); if (newPassword == null || newPassword.equals("")) { String msg = "Password can't be null"; throw new NamingException(msg); } else { if (principal == null || principal.equals("")) { String msg = "Principal can't be null"; throw new NamingException(msg); } else { if (ctxAdmin == null) { String errCtx = "Can't get LDAP context"; throw new NamingException(errCtx); } } } BasicAttribute attr = new BasicAttribute("userpassword", newPassword); ModificationItem modItem = new ModificationItem(DirContext.REPLACE_ATTRIBUTE, attr); ModificationItem[] items = new ModificationItem[1]; items[0] = modItem; ctxAdmin.modifyAttributes("cn=" + principal + ",ou=Users,dc=com", items); }

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  • Why aren't my threads start at the same time? Java

    - by Ada
    Hi, I have variable number of threads which are used for parallel downloading. I used this, for(int i = 0; i< sth; i++){ thrList.add(new myThread (parameters)); thrList.get(i).start(); thrList.get(i).join(); } I don't know why but they wait for each other to complete. When using threads, I am supposed get mixed print outs, since right then there are several threads running that code. However, when I print them out, they are always in order and one thread waits for the previous one to finish first. I only want them to join the main thread, not wait for each other. I noticed that when I measured time while downloading in parallel. How can I fix this? Why are they doing it in order? In my .java, there is MyThread class with run and there is Downloader class with static methods and variables. Would they be the cause of this? The static methods and variables? How can I fix this problem?

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  • How to have variables with dynamic data types in Java?

    - by Nazgulled
    Hi, I need to have a UserProfile class that it's just that, a user profile. This user profile has some vital user data of course, but it also needs to have lists of messages sent from the user friends. I need to save these messages in LinkedList, ArrayList, HashMap and TreeMap. But only one at a time and not duplicate the message for each data structure. Basically, something like a dynamic variable type where I could pick the data type for the messages. Is this, somehow, possible in Java? Or my best approach is something like this? I mean, have 2 different classes (for the user profile), one where I host the messages as Map<K,V> (and then I use HashMap and TreeMap where appropriately) and another class where I host them as List<E> (and then I use LinkedList and ArrayList where appropriately). And probably use a super class for the UserProfile so I don't have to duplicate variables and methods for fields like data, age, address, etc... Any thoughts?

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  • PDFBox Pagebreak strange Nullpointer exception

    - by schneiti
    I currently try printing out text on multiple pages. For this, I count the number of rows and when they reach a fixed amount a method called pagebreakis executed. After the first pagebreak, when I try setting a font using contentstream.setFont(PDType1Font.HELVETICA, 12); it yields the following errormessage occuring at the described setFont-row. java.lang.NullPointerException at org.apache.pdfbox.pdmodel.edit.PDPageContentStream.setFont(PDPageContentStream.java:321) at com.xy.deu.xy.abc.db.schemavergleich.PDFDocumenter.drawBGCS(PDFDocumenter.java:781) at com.xy.deu.xy.abc.db.schemavergleich.PDFDocumenter.createPDFDocumentation(PDFDocumenter.java:205) at com.xy.deu.xy.abc.db.schemavergleich.MainClass.createPDFandOutput(MainClass.java:361) at com.xy.deu.xy.abc.db.schemavergleich.MainClass.start(MainClass.java:231) at com.xy.deu.xy.abc.db.schemavergleich.MainClass.main(MainClass.java:180) Below is the code that gets executed as the error occurs. ... // If Table gets to long for a page -> pagebreak: if(currentLines > 37) { pageBreak(currentLinePos); // TODO Currently causing app to crash } ... private void pageBreak(int currentLine) throws Exception { contentStream.endText(); contentStream.close(); // Create new page page = new PDPage(PDPage.PAGE_SIZE_A4); doc.addPage( page ); // Create a new font object selecting one of the PDF base fonts font = PDType1Font.HELVETICA; // Start a new content stream which will "hold" the to be created content contentStream = new PDPageContentStream(doc, page); currentLines = 0; mediabox = page.findMediaBox(); contentStream.beginText(); contentStream.moveTextPositionByAmount(startX, startY); contentStream.setFont(PDType1Font.HELVETICA, 12); } Now comes the strange thing: Debugging yields into nothing that is not set. I'll attach a screenshot for you right at the position where the error occurs:

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  • How to iteratively generate k elements subsets from a set of size n in java?

    - by Bea Metitiri
    Hi, I'm working on a puzzle that involves analyzing all size k subsets and figuring out which one is optimal. I wrote a solution that works when the number of subsets is small, but it runs out of memory for larger problems. Now I'm trying to translate an iterative function written in python to java so that I can analyze each subset as it's created and get only the value that represents how optimized it is and not the entire set so that I won't run out of memory. Here is what I have so far and it doesn't seem to finish even for very small problems: public static LinkedList<LinkedList<Integer>> getSets(int k, LinkedList<Integer> set) { int N = set.size(); int maxsets = nCr(N, k); LinkedList<LinkedList<Integer>> toRet = new LinkedList<LinkedList<Integer>>(); int remains, thresh; LinkedList<Integer> newset; for (int i=0; i<maxsets; i++) { remains = k; newset = new LinkedList<Integer>(); for (int val=1; val<=N; val++) { if (remains==0) break; thresh = nCr(N-val, remains-1); if (i < thresh) { newset.add(set.get(val-1)); remains --; } else { i -= thresh; } } toRet.add(newset); } return toRet; } Can anybody help me debug this function or suggest another algorithm for iteratively generating size k subsets? EDIT: I finally got this function working, I had to create a new variable that was the same as i to do the i and thresh comparison because python handles for loop indexes differently.

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  • Is there a Java data structure that is effectively an ArrayList with double indicies and built-in in

    - by Bob Cross
    I am looking for a pre-built Java data structure with the following characteristics: It should look something like an ArrayList but should allow indexing via double-precision rather than integers. Note that this means that it's likely that you'll see indicies that don't line up with the original data points (i.e., asking for the value that corresponds to key "1.5"). As a consequence, the value returned will likely be interpolated. For example, if the key is 1.5, the value returned could be the average of the value at key 1.0 and the value at key 2.0. The keys will be sorted but the values are not ensured to be monotonically increasing. In fact, there's no assurance that the first derivative of the values will be continuous (making it a poor fit for certain types of splines). Freely available code only, please. For clarity, I know how to write such a thing. In fact, we already have an implementation of this and some related data structures in legacy code that I want to replace due to some performance and coding issues. What I'm trying to avoid is spending a lot of time rolling my own solution when there might already be such a thing in the JDK, Apache Commons or another standard library. Frankly, that's exactly the approach that got this legacy code into the situation that it's in right now.... Is there such a thing out there in a freely available library?

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  • How to implement the API/SPI Pattern in Java?

    - by Adam Tannon
    I am creating a framework that exposes an API for developers to use: public interface MyAPI { public void doSomeStuff(); public int getWidgets(boolean hasRun); } All the developers should have to do is code their projects against these API methods. I also want them to be able to place different "drivers"/"API bindings" on the runtime classpath (the same way JDBC or SLF4J work) and have the API method calls (doSomeStuff(), etc.) operate on different 3rd party resources (files, servers, whatever). Thus the same code and API calls will map to operations on different resources depending on what driver/binding the runtime classpath sees (i.e. myapi-ftp, myapi-ssh, myapi-teleportation). How do I write (and package) an SPI that allows for such runtime binding, and then maps MyAPI calls to the correct (concrete) implementation? In other words, if myapi-ftp allows you to getWidgets(boolean) from an FTP server, how would I could this up (to make use of both the API and SPI)? Bonus points for concrete, working Java code example! Thanks in advance!

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  • Learning Java and logic using debugger. Did I cheat?

    - by centr0
    After a break from coding in general, my way of thinking logically faded (as if it was there to begin with...). I'm no master programmer. Intermediate at best. I decided to see if i can write an algorithm to print out the fibonacci sequence in Java. I got really frustrated because it was something so simple, and used the debugger to see what was going on with my variables. solved it in less than a minute with the help of the debugger. Is this cheating? When I read code either from a book or someone else's, I now find that it takes me a little more time to understand. If the alghorithm is complex (to me) i end up writing notes as to whats going on in the loop. A primitive debugger if you will. When you other programmers read code, do you also need to write things down as to whats the code doing? Or are you a genius and and just retain it?

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  • Java: How do I implement a method that takes 2 arrays and returns 2 arrays?

    - by HansDampf
    Okay, here is what I want to do: I want to implement a crossover method for arrays. It is supposed to take 2 arrays of same size and return two new arrays that are a kind of mix of the two input arrays. as in [a,a,a,a] [b,b,b,b] ------ [a,a,b,b] [b,b,a,a]. Now I wonder what would be the suggested way to do that in Java, since I cannot return more than one value. My ideas are: - returning a Collection(or array) containing both new arrays. I dont really like that one because it think would result in a harder to understand code. - avoiding the need to return two results by calling the method for each case but only getting one of the results each time. I dont like that one either, because there would be no natural order about which solution should be returned. This would need to be specified, though resulting in harder to understand code. Plus, this will work only for this basic case, but I will want to shuffle the array before the crossover and reverse that afterwards. I cannot do the shuffling isolated from the crossover since I wont want to actually do the operation, instead I want to use the information about the permutation while doing the crossover, which will be a more efficient way I think.

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  • Java: multi-threaded maps: how do the implementations compare?

    - by user346629
    I'm looking for a good hash map implementation. Specifically, one that's good for creating a large number of maps, most of them small. So memory is an issue. It should be thread-safe (though losing the odd put might be an OK compromise in return for better performance), and fast for both get and put. And I'd also like the moon on a stick, please, with a side-order of justice. The options I know are: HashMap. Disastrously un-thread safe. ConcurrentHashMap. My first choice, but this has a hefty memory footprint - about 2k per instance. Collections.sychronizedMap(HashMap). That's working OK for me, but I'm sure there must be faster alternatives. Trove or Colt - I think neither of these are thread-safe, but perhaps the code could be adapted to be thread safe. Any others? Any advice on what beats what when? Any really good new hash map algorithms that Java could use an implementation of? Thanks in advance for your input!

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  • Can I make a derived class inherit a derived member from its base class in Java?

    - by Eric
    I have code that looks like this: public class A { public void doStuff() { System.out.print("Stuff successfully done"); } } public class B extends A { public void doStuff() { System.out.print("Stuff successfully done, but in a different way"); } public void doMoreStuff() { System.out.print("More advanced stuff successully done"); } } public class AWrapper { public A member; public AWrapper(A member) { this.member = member; } public void doStuffWithMember() { a.doStuff(); } } public class BWrapper extends AWrapper { public B member; public BWrapper(B member) { super(member); //Pointer to member stored in two places: this.member = member; //Not great if one changes, but the other does not } public void doStuffWithMember() { member.doMoreStuff(); } } However, there is a problem with this code. I'm storing a reference to the member in two places, but if one changes and the other does not, there could be trouble. I know that in Java, an inherited method can narrow down its return type (and perhaps arguments, but I'm not certain) to a derived class. Is the same true of fields?

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  • Java ORM related question - SQL Vs Google DB (Big Table?) GAE

    - by StackerFlow
    I was wondering about the following two options when one is not using SQL tables but ORM based DBs (Example - when you are using GAE) Would the second option be less efficient? Requirement: There is an object. The object has a collection of similar items. I need to store this object. Example, say the object is a tree and it has a collection of leaves. Option 1: Traditional SQL type structure: Table for the Tree (with TreeId as the identifier for a row in the Table.) Table for the Leaves (where each leaf has a TreeId and to show the leaves of a tree, I query all leaves where the TreeId is the Id of the tree.) Here, the Tree structure DOES NOT have a field with leaves. Option 2: ORM / GAE Tables: Using the same example above, I have an object for Tree where the object has a collection (Set/List in Java/C++) of leaves. I store and retrieve the Tree together with the leaves (as the leaves are implemented as a Set in the Tree object) My question is, will the second one be less efficient that the first option? If so, why? Are there other alternatives? Thank you!

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  • How can I make my code work in a GUI using Swing in Java?

    - by Razor Shadow
    I'm making a tool that does multiple things, and I'm onto the last feature for now: You type in a date and it tells you what day of the week it would be on that date. So I have two problems here: I can't use I can't use arguments, it doesn't like them On the last line, I can't use jTextArea2.setText(d0); because it doesn't like that either... My code is here: public static void main(String[] args) { int d = Integer.parseInt(args[0]); int m = Integer.parseInt(args[1]); int y = Integer.parseInt(args[2]); int y0 = y - (14 - m) / 12; int x = y0 + y0/4 - y0/100 + y0/400; int m0 = m + 12 * ((14 - m) / 12) - 2; int d0 = (d + x + (31*m0)/12) % 7; System.out.println("Sunday = 0\nMonday = 1\nTuesday = 2\nWednesday = 3\nThursday = 4\nFriday = 5\nSaturday = 6\nThis date is on a:"); System.out.println(d0); Basically, this code was at first for use with the console, and now I want to implement it into a Swing GUI app. I'm only a week into learning Java, so excuse me if the problem is obvious or easy to fix... But can anyone figure out how to work it? Thanks!

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  • Filling in uninitialized array in java? (or workaround!)

    - by AlexRamallo
    Hello all, I'm currently in the process of creating an OBJ importer for an opengles android game. I'm relatively new to the language java, so I'm not exactly clear on a few things. I have an array which will hold the number of vertices in the model(along with a few other arrays as well): float vertices[]; The problem is that I don't know how many vertices there are in the model before I read the file using the inputstream given to me. Would I be able to fill it in as I need to like this?: vertices[95] = 5.004f; //vertices was defined like the example above or do I have to initialize it beforehand? if the latter is the case then what would be a good way to find out the number of vertices in the file? Once I read it using inputstreamreader.read() it goes to the next line until it reads the whole file. The only thing I can think of would be to read the whole file, count the number of vertices, then read it AGAIN the fill in the newly initialized array. Is there a way to dynamically allocate the data as is needed?

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  • How do I use requestFocus in a Java JFrame GUI?

    - by JohnWong
    I am given an assignment but I am totally new to Java (I have been programming in C++ and Python for two years). So we are doing GUI and basically we extended JFrame and added a couple fields. Say we have a field named "Text 1" and "Text 2". When user presses enter with the cursor in Text 1, move the focus to Text 2. I tried to add private JTextField textfield1() { textfield1 = new JTextField(); textfield1.setPreferredSize(new Dimension(200, 20)); textfield1.addActionListener( new ActionListener() { public void actionPerformed(ActionEvent e) { textfield1text = textfield1.getText().trim(); textfield1.setText(textfield1text); System.out.println(textfield1text); textfield1.requestFocus(); } }); return textfield1; } But that doesn't work at all. I noticed that requestFocus is not recommended, and instead one should use requestFocusWindows. But I tried that too. Upon some readings it seems like I have to do keyboard action and listener? But my teacher said it only requires 1 line...

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  • junit test error - ClassCastException

    - by Josepth Vodary
    When trying to run a junit test I get the following error - java.lang.ClassCastException: business.Factory cannot be cast to services.itemservice.IItemsService at business.ItemManager.get(ItemManager.java:56) at business.ItemMgrTest.testGet(ItemMgrTest.java:49) The specific test that is causing the problem is @Test public void testGet() { Assert.assertTrue(itemmgr.get(items)); } The code it is testing is... public boolean get(Items item) { boolean gotItems = false; Factory factory = Factory.getInstance(); @SuppressWarnings("static-access") IItemsService getItem = (IItemsService)factory.getInstance(); try { getItem.getItems("pens", 15, "red", "gel"); gotItems = true; } catch (ItemNotFoundException e) { // catch e.printStackTrace(); System.out.println("Error - Item Not Found"); } return gotItems; } The test to store items, which is nearly identical, works just fine... The factory class is.. public class Factory { private Factory() {} private static Factory Factory = new Factory(); public static Factory getInstance() {return Factory;} public static IService getService(String serviceName) throws ServiceLoadException { try { Class<?> c = Class.forName(getImplName(serviceName)); return (IService)c.newInstance(); } catch (Exception e) { throw new ServiceLoadException(serviceName + "not loaded"); } } private static String getImplName (String serviceName) throws Exception { java.util.Properties props = new java.util.Properties(); java.io.FileInputStream fis = new java.io.FileInputStream("config\\application.properties"); props.load(fis); fis.close(); return props.getProperty(serviceName); } }

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  • JAVA - How to code Node neighbours in a Grid ?

    - by ke3pup
    Hi guys I'm new to programming and as a School task i need to implement BFS,DFS and A* search algorithms in java to search for a given Goal from a given start position in a Grid of given size, 4x4,8x8..etc to begin with i don't know how to code the neighbors of all the nodes. For example tile 1 in grid as 2 and 9 as neighbors and Tile 12 has ,141,13,20 as its neighbours but i'm struggling to code that. I need the neighbours part so that i can move from start position to other parts of gird legally by moving horizontally or vertically through the neighbours. my node class is: class node { int value; LinkedList neighbors; bool expanded; } let's say i'm given a 8x8 grid right, So if i start the program with a grid of size 8x8 right : 1 - my main will func will create an arrayList of nodes for example node ArrayList test = new ArrayList(); and then using a for loop assign value to all the nodes in arrayList from 1 to 64 (if the grid size was 8x8). BUT somehow i need t on coding that, if anyone can give me some details i would really appreciate it.

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  • (Java) Is there a type of object that can handle anything from primitives to arrays?

    - by Michael
    I'm pretty new to Java, so I'm hoping one of you guys knows how to do this. I'm having the user specify both the type and value of arguments, in any XML-like way, to be passed to methods that are external to my application. Example: javac myAppsName externalJavaClass methodofExternalClass [parameters] Of course, to find the proper method, we have to have the proper parameter types as the method may be overloaded and that's the only way to tell the difference between the different versions. Parameters are currently formatted in this manner: (type)value(/type), e.g. (int)71(/int) (string)This is my string that I'm passing as a parameter!(/string) I parse them, getting the constructor for whatever type is indicated, then execute that constructor by running its method, newInstance(<String value>), loading the new instance into an Object. This works fine and dandy, but as we all know, some methods take arrays, or even multi-dimensional arrays. I could handle the argument formatting like so: (array)(array)(int)0(/int)(int)1(/int)(/array)(array)(int)2(/int)(int)3(/int)(/array)(/array)... or perhaps even better... {{(int)0(/int)(int)1(/int)}{(int)2(/int)(int)3(/int)}}. The question is, how can this be implemented? Do I have to start wrapping everything in an Object[] array so I can handle primitives, etc. as argObj[0], but load an array as I normally would? (Unfortunately, I would have to make it an Object[][] array if I wanted to support two-dimensional arrays. This implementation wouldn't be very pretty.)

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  • What does this Java generics paradigm do and what is it called?

    - by Tom
    I'm looking at some Java classes that have the following form: public abstract class A <E extends A<E>> implements Comparable <E> { public final int compareTo( E other ) { // etc } } public class B extends A <B> { // etc } public class C extends A <C> { // etc } My usage of "Comparable" here is just to illustrate a possible use of the generic parameter "E". Does this usage of generics/inheritance have a name? What is it used for? My impression is that this allows the abstract class to provide a common implementation of a method (such as compareTo) without having to provide it in the subclasses. However, in this example, unlike an inherited method it would restrict subclasses to invoking compareTo on other instances of the same subclass, rather than any "A" subclass. Does this sound right? Anyway, just curious if any gurus out there have seen this before and know what it does. Thanks!

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  • Why does Java automatically decode %2F in URI encoded filenames?

    - by Lucas
    I have a java servlet that needs to write out files that have a user-configurable name. I am trying to use URI encoding to properly escape special characters, but the JRE appears to automatically convert encoded forward slashes (%2F) into path separators. Example: File dir = new File("C:\Documents and Setting\username\temp"); String fn = "Top 1/2.pdf"; URI uri = new URI( dir.toURI().toASCIIString() + URLEncoder.encoder( fn, "UTF-8" ).toString() ); File out = new File( uri ); System.out.println( dir.toURI().toASCIIString() ); System.out.println( URLEncoder.encoder( fn, "UTF-8" ).toString() ); System.out.println( uri.toASCIIString() ); System.out.println( output.toURI().toASCIIString() ); The output is: file:/C:/Documents%20and%20Settings/username/temp/ Top+1%2F2.pdf file:/C:/Documents%20and%20Settings/username/temp/Top+1%2F2.pdf file:/C:/Documents%20and%20Settings/username/temp/Top+1/2.pdf After the new File object is instantiated, the %2F sequence is automatically converted to a forward slash and I end up with an incorrect path. Does anybody know the proper way to approach this issue? The core of the problem seems to be that uri.equals( new File(uri).toURI() ) == FALSE when there is a '%2F' in the URI. I'm planning to just use the URLEncoded string verbatim rather than trying to use the File(uri) constructor.

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  • A* navigational mesh path finding

    - by theguywholikeslinux
    So I've been making this top down 2D java game in this framework called Greenfoot [1] and I've been working on the AI for the guys you are gonna fight. I want them to be able to move around the world realistically so I soon realized, amongst a couple of other things, I would need some kind of pathfinding. I have made two A* prototypes. One is grid based and then I made one that works with waypoints so now I need to work out a way to get from a 2d "map" of the obstacles/buildings to a graph of nodes that I can make a path from. The actual pathfinding seems fine, just my open and closed lists could use a more efficient data structure, but I'll get to that if and when I need to. I intend to use a navigational mesh for all the reasons out lined in this post on ai-blog.net [2]. However, the problem I have faced is that what A* thinks is the shortest path from the polygon centres/edges is not necessarily the shortest path if you travel through any part of the node. To get a better idea you can see the question I asked on stackoverflow [3]. I got a good answer concerning a visibility graph. I have since purchased the book (Computational Geometry: Algorithms and Applications [4]) and read further into the topic, however I am still in favour of a navigational mesh (See "Managing Complexity" [5] from Amit’s Notes about Path-Finding [6]). (As a side note, maybe I could possibly use Theta* to convert multiple waypoints into one straight line if the first and last are not obscured. Or each time I move back check to the waypoint before last to see if I can go straight from that to this) So basically what I want is a navigational mesh where once I have put it through a funnel algorithm (e.g. this one from Digesting Duck [7]) I will get the true shortest path, rather than get one that is the shortest path following node to node only, but not the actual shortest given that you can go through some polygons and skip nodes/edges. Oh and I also want to know how you suggest storing the information concerning the polygons. For the waypoint prototype example I made I just had each node as an object and stored a list of all the other nodes you could travel to from that node, I'm guessing that won't work with polygons? and how to I tell if a polygon is open/traversable or if it is a solid object? How do I store which nodes make up the polygon? Finally, for the record: I do want to programme this by myself from scratch even though there are already other solutions available and I don't intend to be (re) using this code in anything other than this game so it does not matter that it will inevitably be poor quality. http://greenfoot.org http://www.ai-blog.net/archives/000152.html http://stackoverflow.com/q/7585515/ http://www.cs.uu.nl/geobook/ http://theory.stanford.edu/~amitp/GameProgramming/MapRepresentations.html http://theory.stanford.edu/~amitp/GameProgramming/ http://digestingduck.blogspot.com/2010/03/simple-stupid-funnel-algorithm.html

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