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  • Loading data in constructors and not in constructors [JAVA]

    - by Richeve S. Bebedor
    i just want to know the difference between loading the data inside the constructor and loading the data outside the constructor but not inside any methods example: Loading inside constructor public class Model{ Object testobject; public Model(){ testobject=new Object(); } } VS example: Loading outside constructor public class Model{ Object testobject=new Object(); public Model(){ } }

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  • java singleton instantiation

    - by jurchiks
    I've found three ways of instantiating a Singleton, but I have doubts as to whether any of them is the best there is. I'm using them in a multi-threaded environment and prefer lazy instantiation. Sample 1: private static final ClassName INSTANCE = new ClassName(); public static ClassName getInstance() { return INSTANCE; } Sample 2: private static class SingletonHolder { public static final ClassName INSTANCE = new ClassName(); } public static ClassName getInstance() { return SingletonHolder.INSTANCE; } Sample 3: private static ClassName INSTANCE; public static synchronized ClassName getInstance() { if (INSTANCE == null) INSTANCE = new ClassName(); return INSTANCE; } The project I'm using ATM uses Sample 2 everywhere, but I kind of like Sample 3 more. There is also the Enum version, but I just don't get it. The question here is - in which cases I should/shouldn't use any of these variations? I'm not looking for lengthy explanations though (there's plenty of other topics about that, but they all eventually turn into arguing IMO), I'd like it to be understandable with few words.

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  • How is Java Process.getOutputStream() Implemented?

    - by Amit Kumar
    I know the answer depends on the particular JVM, but I would like to understand how it is usually implemented? Is it in terms of popen (posix)? In terms of efficiency do I need to keep something in mind (other than using a Buffered stream as suggested by the javadoc). I would be interested to know if there is a general reference about implementations of JVMs which answers such questions.

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  • using regular expression in Java

    - by Mrityunjay
    Hi, i need to check a string that should contain only ABCDEFG characters, in any sequence and with only 7 characters. Please let me know the correct way of using regular expression. as corrently i am using String abs = "ABPID"; if(!Pattern.matches("[[ABCDEFG]", abs)) System.out.println("Error"); i am using the following code which works when i use the String abcdefg but for other cases it fails. please help me out.

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  • Reading in bytes produced by PHP script in Java to create a bitmap

    - by Kareem
    I'm having trouble getting the compressed jpeg image (stored as a blob in my database). here is the snippet of code I use to output the image that I have in my database: if($row = mysql_fetch_array($sql)) { $size = $row['image_size']; $image = $row['image']; if($image == null){ echo "no image!"; } else { header('Content-Type: content/data'); header("Content-length: $size"); echo $image; } } here is the code that I use to read in from the server: URL sizeUrl = new URL(MYURL); URLConnection sizeConn = sizeUrl.openConnection(); // Get The Response BufferedReader sizeRd = new BufferedReader(new InputStreamReader(sizeConn.getInputStream())); String line = ""; while(line.equals("")){ line = sizeRd.readLine(); } int image_size = Integer.parseInt(line); if(image_size == 0){ return null; } URL imageUrl = new URL(MYIMAGEURL); URLConnection imageConn = imageUrl.openConnection(); // Get The Response InputStream imageRd = imageConn.getInputStream(); byte[] bytedata = new byte[image_size]; int read = imageRd.read(bytedata, 0, image_size); Log.e("IMAGEDOWNLOADER", "read "+ read + " amount of bytes"); Log.e("IMAGEDOWNLOADER", "byte data has length " + bytedata.length); Bitmap theImage = BitmapFactory.decodeByteArray(bytedata, 0, image_size); if(theImage == null){ Log.e("IMAGEDOWNLOADER", "the bitmap is null"); } return theImage; My logging shows that everything has the right length, yet theImage is always null. I'm thinking it has to do with my content type. Or maybe the way I'm uploading?

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  • Show users a list of unique items on Java Google App Engine

    - by James
    I've been going round in circles with what must be a very simple challenge but I want to do it the most efficient way from the start. So, I've watched Brett Slatkin's Google IO videos (2008 & 2009) about building scalable apps including http://www.youtube.com/watch?v=AgaL6NGpkB8 and read the docs but as a n00b, I'm still not sure. I'm trying to build an app on GAEJ similar to the original 'hotornot' where a user is presented with an item which they rate. Once they rate it, they are presented with another one which they haven't seen before. My question is this; is it most efficient to do a query up front to grab x items (say 100) and put them in a list (stored in memcache?) or is it better to simply make a query for a new item after each rating. To keep track of the items a user has seen, I'm planning to keep those items' keys in a list property of the user's entity. Does that sound sensible? I've really got myself confused about this so any help would be much appreciated.

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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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  • Joining remote paths in Java

    - by Mickael Marrache
    I'm using the FTP library provided by Apache (commons-net). I want to check if a file exists on the FTP server so I use the listFiles method of FTPClient: ftpClient.listFiles(remoteFileDir + "\\" + fileName); The current directory is the FTP server root directory. So, the value of remoteFileDir is a path relative to this root directory. My question concerns the merge between the remote directory path and the file name. What is the right way to do it? For a local file, I would do: File file = new File(remoteFileDir,fileName); but here it doesn't work since when I call file.getAbsolutePath(), I get an absolute path for the file in the local current directory which is not what I want. Also, I guess the merging has been done according to my local environment. PS: I looked at How are paths determined on a remote machines? but it doesn't help me. Thanks

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  • Deleting from arraylist and exporting back to .buab file(Java)

    - by Dave
    Ive made an address book. I can currently write to the arraylist and save it back to the .buab file, but I cant delete from the arraylist and export it back to the .buab file? Im pretty much stuck on this. Im able to retrive contacts from the .buab and scroll through them using the JTextFields and buttons ive created. Any help will be dearly appreciated. Ive set up seprate classes for all operations (newcontacts, nextcontact etc). If you need the code posted let me know.. Cheers Dave

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  • Lines don't overlap when they should Java Swing

    - by Sven
    I'm drawing lines in a JFrame on a self made gridPanel. Problem is, I draw the lines between 2 points. When I have a line that is between point 1 and point 2 and a line between point 2 and point 3, the lines should connect. This however isn,t the case, there is a small gap in between, no idea why. But it isn't drawing till the end of the specified point. (start point is correct.) Here is the code of the JFrame: public void initialize(){ this.setLayout(new BorderLayout()); this.setPreferredSize(new Dimension(500, 400)); gridPane = new GridPane(); gridPane.setBackground(Color.WHITE); gridPane.setSize(this.getPreferredSize()); gridPane.setLocation(0, 0); this.add(gridPane,BorderLayout.CENTER); //createSampleLabyrinth(); drawWall(0,5,40,5); //These are the 2 lines that don't connect. drawWall(40,5,80,5); this.pack(); } drawWall calls a method that calls a method in GridPane. The relevant code in gridPane: /** * Draws a wall on this pane. With the starting point being x1, y1 and its end x2,y2. * @param x1 * @param y1 * @param x2 * @param y2 */ public void drawWall(int x1, int y1, int x2, int y2) { Wall wall = new Wall(x1,y1,x2,y2, true); wall.drawGraphic(); wall.setLocation(x1, y1); wall.setSize(10000,10000); this.add(wall, JLayeredPane.DEFAULT_LAYER); this.repaint(); } This method creates a wall and puts it in the Jframe. The relevant code of the wall: public class Wall extends JPanel { private int x1; private int x2; private int y1; private int y2; private boolean black; /** * x1,y1 is the start point of the wall (line) end is x2,y2 * * @param x1 * @param y1 * @param x2 * @param y2 */ public Wall(int x1, int y1, int x2, int y2, boolean black) { this.x1 = x1; this.x2 = x2; this.y1 = y1; this.y2 = y2; this.black = black; setOpaque(false); } private static final long serialVersionUID = 1L; public void drawGraphic() { repaint(); } public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2 = (Graphics2D) g; if(black){ g2.setColor(Color.BLACK); g2.setStroke(new BasicStroke(8)); } else { g2.setColor(Color.YELLOW); g2.setStroke(new BasicStroke(3)); } g2.drawLine(x1, y1, x2, y2); } } So, where am I going wrong? The true/false is to determine if the wall should be black or yellow, nothing to be concerned about.

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  • "Dynamic" java validation framework?

    - by pihentagy
    AFAIK JSR-303 is the standard bean validation system. I don't know whether it could do validations like this (I guess no): if an object has a deleted flag set, you cannot modify the object you cannot change the start date property, after the date is passed you cannot decrease some integer properties in the bean So how can I handle validations, which depend on the previous state of an object? I would like to solve problems like that in hibernate3.5 - spring3 - JPA2 environment. Thanks My solution was to mess with hibernate, reload the object to see the old state (after evicting the new object). This time I need some smarter solution...

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  • Override Java System.currentTimeMillis

    - by Mike Clark
    Is there a way, either in code or with JVM arguments, to override the current time, as presented via System.currentTimeMillis, other than manually changing the system clock on the host machine? A little background: We have a system that runs a number of accounting jobs that revolve much of their logic around the current date (ie 1st of the month, 1st of the year, etc) Unfortunately, a lot of the legacy code calls functions such as new Date() or Calendar.getInstance(), both of which eventually call down to System.currentTimeMillis. For testing purposes, right now, we are stuck with manually updating the system clock to manipulate what time and date the code thinks that the test is being run. So my question is: Is there a way to override what is returned by System.currentTimeMillis? For example, to tell the JVM to automatically add or subtract some offset before returning from that method? Thanks in advance!

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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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  • Getting Raw XML From SOAPMessage in Java

    - by Daniel Lew
    I've set up a SOAP WebServiceProvider in JAX-WS, but I'm having trouble figuring out how to get the raw XML from a SOAPMessage (or any Node) object. Here's a sample of the code I've got right now, and where I'm trying to grab the XML: @WebServiceProvider(wsdlLocation="SoapService.wsdl") @ServiceMode(value=Service.Mode.MESSAGE) public class SoapProvider implements Provider<SOAPMessage> { public SOAPMessage invoke(SOAPMessage msg) { // How do I get the raw XML here? } } Is there a simple way to get the XML of the original request? If there's a way to get the raw XML by setting up a different type of Provider (such as Source), I'd be willing to do that, too.

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  • Java - Calling all methods of a class

    - by Thomas Eschemann
    I'm currently working on an application that has to render several Freemarker templates. So far I have a Generator class that handles the rendering. The class looks more or less like this: public class Generator { public static void generate(…) { renderTemplate1(); renderTemplate2(); renderTemplate3(); } private static void render(…) { // renders the template } private static void renderTemplate1() { // Create config object for the rendering // and calls render(); }; private static void renderTemplate1() { // Create config object for the rendering // and calls render(); }; … } This works, but it doesn't really feel right. What I would like to do is create a class that holds all the renderTemplate...() methods and then call them dynamically from my Generator class. This would make it cleaner and easier to extend. I was thinking about using something like reflection, but it doesn't really feel like a good solution either. Any idea on how to implement this properly ?

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  • Implementing java FixedTreadPool status listener

    - by InsertNickHere
    Hi there, it's about an application which is supposed to process (VAD, Loudness, Clipping) a lot of soundfiles (e.g. 100k). At this time, I create as many worker threads (callables) as I can put into memory, and then run all with a threadPool.invokeAll(), write results to file system, unload processed files and continue at step 1. Due to the fact it's an app with a GUI, i don't want to user to feel like the app "is not responding" while processing all soundfiles. (which it does at this time cause invokeAll is blocking). Im not sure what is a "good" way to fix this. It shall not be possible for the user to do other things while processing, but I'd like to show a progress bar like "10 of 100000 soundfiles are done". So how do I get there? Do I have to create a "watcher thread", so that every worker hold a callback on it? I'm quite new to multi threading, and don't get the idea of such a mechanisem.. If you need to know: I'm using SWT/JFace. Regards, InsertNickHere

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  • Is java.util.Scanner that slow?

    - by Cristian Vrabie
    Hi guys, In a Android application I want to use Scanner class to read a list of floats from a text file (it's a list of vertex coordinates for OpenGL). Exact code is: Scanner in = new Scanner(new BufferedInputStream(getAssets().open("vertexes.off"))); final float[] vertexes = new float[nrVertexes]; for(int i=0;i<nrVertexFloats;i++){ vertexes[i] = in.nextFloat(); } It seems however that this is incredibly slow (it took 30 minutes to read 10,000 floats!) - as tested on the 2.1 emulator. What's going on? I don't remember Scanner to be that slow when I used it on the PC (truth be told I never read more than 100 values before). Or is it something else, like reading from an asset input stream? Thanks for the help!

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  • Java JEditorPane

    - by ikurtz
    ChatGUI im using 2 JEditorPane to transfer text from one to another. once i have transfered the data i do the following: JEditorPane.setText(null); JEditorPane.setCaretPosition(0); but as you can see from the attached image the return action makes the prompt appear a row down. how can i fix this?

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  • Java Conversion of byte[] into a srting and then back to a byte[]

    - by Sid
    I am working on a proxy server. I am getting data in byte[] which i convert into a string to perform certain operations. Now when i convert this new string back into a byte [] it causes unkonw problems. So mainly its like i need to know how to correctly convert a byte[] into a string and then back into a byte[] again. I tried to just convert the byte[] to string and then back to byte[] again (to make sure thats its not my operations that are causing problems). So its like: // where reply is a byte[] String str= new String(reply,0, bytesRead); streamToClient.write(str.getBytes(), 0, bytesRead); is not equivalent to streamToClient.write(reply, 0, bytesRead); my proxy works fine when i just send the byte[] without any conversion but when i convert it from byte[] to a string and then back to a byte[] its causes problems. can some one please help? =]

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  • Stateful Iterators Java

    - by Gitmo
    What is a Stateful Iterator? This question relates to an Iterator defined in Hadoop for performing Joins. As the reference documentation states: This defines an interface to a stateful Iterator that can replay elements added to it directly. Note that this does not extend Iterator. What does 'replay elements added to it directly' mean? How is this iterator different from a usual iterator?

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