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  • Cast element in Java For Each statement

    - by Carl Summers
    Is it possible (or even advisable) to cast the element retrieved from a for each statement in the statement itself? I do know that each element in list will be of type . I.E.: List<BaseType> list = DAO.getList(); for(<SubType> element : list){ // Cannot convert from element type <BaseType> to <SubType> ... } rather than: List <BaseType> list = DAO.getList(); for(<BaseType> el : list){ <SubType> element = (<SubType>)el; ... }

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  • Java - Thread problem

    - by Yatendra Goel
    My question is related to all those methods(including Thread.sleep(...)) which throw InterruptedException. I found a statement on Sun's tutorial saying InterruptedException is an exception that sleep throws when another thread interrupts the current thread while sleep is active. Is that means that the interrupt will be ignored if the sleep is not active at the time of interrupt? Suppose I have two threads: threadOne and threadTwo. threadOne creates and starts threadTwo. threadTwo executes a runnable whose run method is something like: public void run() { : : try { Thread.sleep(10 * 1000); } catch (InterruptedException e) { return; } : : : // In the middle of two sleep invocations : : try { Thread.sleep(10 * 1000); } catch (InterruptedException e) { return; } : : } After thread creation, threadOne interrupts threadTwo. Suppose the threadTwo is in the middle of two sleep invocations at the time of interrupt (when no sleep method was active), then will the second sleep method throw InterrupteException as soon as it is invoked? If not, then will this interrupt will be ignored forever? How to be sure that threadTwo will always know about the interrupt (doesn't matter whether its one of the sleep method is active or not)?

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  • Dynamic Clock in java

    - by jt153
    I want to implement a clock within my program to diusplay the date and time while the program is running. I have looked into the getCurrentTime() method and timers but none of them seem to do what I would like. The problem is I can get the current time when the program loads but it never updates. Any suggestions on something to look into would be greatly appreciated!

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  • Java Enum List from Class

    - by DD
    How do I go from a Class object to a list of enums generically? i.e. public static <T extends Enum> List<T> getList(Class<T> clazz) I cant find a way to get to the values() method

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  • Java fixed memory map

    - by juber
    Hi, Is there a simple, efficient Map implementation that allows a limit on the memory to be used by the map. My use case is that I want to allocate dynamically most of the memory available at the time of its creation but I don't want OutOFMemoryError at any time in future. Basically, I want to use this map as a cache, but but I wanna avoid heavy cache implementations like EHCache. My need is simple (at most an LRU algorithm)

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  • Java - Circular Garbage Collection

    - by aloh
    A <- B <- C <- D <- A... // A is firstNode, D is lastNode if ( length == 1 ) { firstNode = null; lastNode = null; firstNode.next = null; firstNode.prev = null; } else { Node secondNode = firstNode.next; Node secondToLast = lastNode.prev; firstNode.next = null; firstNode.prev = null; lastNode.next = null; lastNode.prev = null; secondNode.prev = null; secondToLast.next = null; firstNode = null; lastNode = null; } That should send everything in between as candidates for garbage collection, I hope?

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  • UTF-8 character encoding in Java

    - by user332523
    Hello, I am having some problems getting some French text to convert to UTF8 so that it can be displayed properly, either in a console, text file or in a GUI element. The original string is HANDICAP+ES which is supposed to be HANDICAPÉES No matter how I tried converting it, it appears the same way. Any ideas on how I can do this conversion? Thanks, Cam

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  • Cookie questions in Java

    - by user220201
    Hi, How do I differentiate between multiple cookies set through my site? I am setting two kinds of cookies one to see if the user has visited the site or not and an other one for authentication. How do I differentiate between these two? I get both of them when someone accesses a page after authentication. Do I add extra information to the Cookie Value or is there some other way? I understand the setName() function will change the name (from jsessionid) for every cookie from then on. Am I correct? Pav

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  • Create java sandbox based on security policies

    - by argos
    I need to create environment to run potentially untrusted code. Program allowed to connect to preconfigured address:port and nothing else (even read the system time). I have compiled the class whitelist. I'd searched similar questions, but found only template that based on SecurityManager which AFAIK is deprecated. Can anybody give me a simple sample how to run code in sandbox based on security policies and AccessController?

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  • Simple java synchronization question

    - by Misha Koshelev
    I was wondering, which is correct: Option One class A { public void methodOne() { synchronized(this) { modifyvalue notifyAll() } } public void methodTwo() { while (valuenotmodified) { synchronized(this) { wait() } } } Option Two class A { public void methodOne() { modifyvalue synchronized(this) { notifyAll() } } public void methodTwo() { while (valuenotmodified) { synchronized(this) { wait() } } } and why?

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  • Java String.split

    - by user903772
    I have the following text: ARIYALUR:ARIYALUR|CHENNAI:CHENNAI|COIMBATORE:COIMBATORE|CUDDALORE:CUDDALORE|DINDIGUL:DINDIGUL|ERODE:ERODE|KANCHEEPURAM:KANCHEEPURAM|KANYAKUMARI:KANYAKUMARI|KRISHNAGIRI:KRISHNAGIRI|MADURAI:MADURAI|NAMAKKAL:NAMAKKAL|NILGIRIS:NILGIRIS|PERAMBALUR:PERAMBALUR|PONDICHERRY:PONDICHERRY|SALEM:SALEM|THANJAVUR:THANJAVUR|THENI:THENI|THIRUVALLUR:THIRUVALLUR|THOOTHUKUDI:THOOTHUKUDI|TIRUNELVELI:TIRUNELVELI|VELLORE:VELLORE|VILLUPURAM:VILLUPURAM|VIRUDHUNAGAR:VIRUDHUNAGAR| I tried to do a split("|") but my array is made up of alphabets and not each district. Please help.

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  • Dijkstra's Algorithm explanation java

    - by alchemey89
    Hi, I have found an implementation for dijkstras algorithm on the internet and was wondering if someone could help me understand how the code works. Many thanks private int nr_points=0; private int[][]Cost; private int []mask; private void dijkstraTSP() { if(nr_points==0)return; //algorithm=new String("Dijkstra"); nod1=new Vector(); nod2=new Vector(); weight=new Vector(); mask=new int[nr_points]; //initialise mask with zeros (mask[x]=1 means the vertex is marked as used) for(int i=0;i<nr_points;i++)mask[i]=0; //Dijkstra: int []dd=new int[nr_points]; int []pre=new int[nr_points]; int []path=new int[nr_points+1]; int init_vert=0,pos_in_path=0,new_vert=0; //initialise the vectors for(int i=0;i<nr_points;i++) { dd[i]=Cost[init_vert][i]; pre[i]=init_vert; path[i]=-1; } pre[init_vert]=0; path[0]=init_vert; pos_in_path++; mask[init_vert]=1; for(int k=0;k<nr_points-1;k++) { //find min. cost in dd for(int j=0;j<nr_points;j++) if(dd[j]!=0 && mask[j]==0){new_vert=j; break;} for(int j=0;j<nr_points;j++) if(dd[j]<dd[new_vert] && mask[j]==0 && dd[j]!=0)new_vert=j; mask[new_vert]=1; path[pos_in_path]=new_vert; pos_in_path++; for(int j=0;j<nr_points;j++) { if(mask[j]==0) { if(dd[j]>dd[new_vert]+Cost[new_vert][j]) { dd[j]=dd[new_vert]+Cost[new_vert][j]; } } } } //Close the cycle path[nr_points]=init_vert; //Save the solution in 3 vectors (for graphical purposes) for(int i=0;i<nr_points;i++) { nod1.addElement(path[i]); nod2.addElement(path[i+1]); weight.addElement(Cost[path[i]][path[i+1]]); } }

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  • Sending files from server to client in Java

    - by Lee Jacobson
    Hi, I'm trying to find a way to send files of different file types from a server to a client. I have this code on the server to put the file into a byte array: File file = new File(resourceLocation); byte[] b = new byte[(int) file.length()]; FileInputStream fileInputStream; try { fileInputStream = new FileInputStream(file); try { fileInputStream.read(b); } catch (IOException ex) { System.out.println("Error, Can't read from file"); } for (int i = 0; i < b.length; i++) { fileData += (char)b[i]; } } catch (FileNotFoundException e) { System.out.println("Error, File Not Found."); } I then send fileData as a string to the client. This works fine for txt files but when it comes to images I find that although it creates the file fine with the data in, the image won't open. I'm not sure if I'm even going about this the right way. Thanks for the help.

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  • Class unloading in java

    - by java_geek
    When a classloader is garbage collected, are the classes loaded by it unloaded? When the JVM is running is verbose mode, all the loaded classes are o/p. Similarly will the JVM log when it unloads a class? I wrote a custom class loader to test this, but could not see any verbose log for unloading of the classes. CustomClassLoader loader = new CustomClassLoader(new URL[]{}, CustomClassLoader.class.getClassLoader()); loader.addURL("D:\workspace\ClassLoaderTest\implementation.jar"); Class c = null; try { c = Class.forName("Horse",false,loader); if (c != null) { try { Animal animal = (Animal)c.newInstance(); animal.eat(); } catch(Exception ex) { ex.printStackTrace(); } } } catch(Exception e) { e.printStackTrace(); } loader = null; byte[] b = new byte[58*1024*1024]; System.gc(); ClassLoadingMXBean clBean = ManagementFactory.getClassLoadingMXBean(); System.out.println("Number of classes currently loaded " + clBean.getLoadedClassCount()); System.out.println("Number of classes loaded totally " + clBean.getTotalLoadedClassCount()); System.out.println("Number of classes unloaded " + clBean.getUnloadedClassCount()); Even the ClassLoadingMXBean gives number of unloaded classes as 0. How can i know that a class is unloaded when the class loader is GCed?

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  • How to synchronize java code

    - by Milan
    I have the next code: Process p = Runtime.getRuntime().exec(args); and I want my program to wait for the Runtime.getRuntime().exec(args); to finish cause it last 2-3sec and then to continue. Ideas?

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  • Insert code into a method - Java

    - by DutrowLLC
    Is there a way to automatically insert code into a method? I have the following and I would like to insert the indicated code: public class Person { Set<String> updatedFields = new LinkedHashSet<String>(); String firstName; public String getFirstName(){ return firstName; } boolean isFirstNameChanged = false; // Insert public void setFirstName(String firstName){ if( !isFirstNameChanged ){ // Insert isFirstNameChanged = true; // Insert updatedFields.add("firstName"); // Insert } // Insert this.firstName = firstName; } } I'm also not sure if I can the subset of the method name as a string from inside the method itself as indicated on the line where I add the fieldName as a string into the set of updated fields: updatedFields.add("firstName");. And I'm not sure how to insert fields into a class where I add the boolean field that tracks if the field has been modified or not before (for efficiency to prevent having to manipulate the Set): boolean isFirstNameChanged = false; It seems to most obvious answer to this would be to use code templates inside eclipse, but I'm concerned about having to go back and change the code later.

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  • Java How to get exact tile location in random tile engine

    - by SYNYST3R1
    I am using the slick2d library. I want to know how to get the exact tile location so when I click on a tile it only changes that tile and not every tile on the screen. My tile generation class public Image[] tiles = new Image[3]; public int width, height; public int[][] index; public Image grass, dirt, selection; boolean selected; int mouseX, mouseY; public void init() throws SlickException { grass = new Image("assets/tiles/grass.png"); dirt = new Image("assets/tiles/dirt.png"); selection = new Image("assets/tiles/selection.png"); tiles[0] = grass; tiles[1] = dirt; width = 50; height = 50; index = new int[width][height]; Random rand = new Random(); for (int x = 0; x < width; x++) { for (int y = 0; y < height; y++) { index[x][y] = rand.nextInt(2); } } } public void update(GameContainer gc) { Input input = gc.getInput(); mouseX = input.getMouseX(); mouseY = input.getMouseY(); if(input.isMouseButtonDown(Input.MOUSE_LEFT_BUTTON)) { selected = true; } else{ selected = false; } } public void render() { for (int x = 0; x < width; x++) { for (int y = 0; y < height; y++) { tiles[index[x][y]].draw(x * 64, y *64); if(IsMouseInsideTile(x, y)) selection.draw(x * 64, y * 64); } } } public boolean IsMouseInsideTile(int x, int y) { return (mouseX >= x * 64 && mouseX <= (x + 1) * 64 && mouseY >= y * 64 && mouseY <= (y + 1) * 64); } I have tried a couple different ways to change the tile I am clicking on, but I don't understand how to do it.

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