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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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  • 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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  • Java - FontMetrics without Graphics

    - by subSeven
    Hello! How to get FontMetrics without use Graphics ? I want to get FontMetrics in constructor, now I do this way: BufferedImage bi = new BufferedImage(5, 5, BufferedImage.TYPE_INT_RGB); FontMetrics fm = bi.getGraphics().getFontMetrics(font); int width = fm.stringWidth(pattern); int height = fm.getHeight();

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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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  • java: relationship of the Runnable and Thread interfaces

    - by Karl Patrick
    I realize that the method run() must be declared because its declared in the Runnable interface. But my question comes when this class runs how is the Thread object allowed if there is no import call to a particular package? how does runnable know anything about Thread or its methods? does the Runnable interface extend the Thread class? Obviously I don't understand interfaces very well. thanks in advance. class PrimeFinder implements Runnable{ public long target; public long prime; public boolean finished = false; public Thread runner; PrimeFinder(long inTarget){ target = inTarget; if(runner == null){ runner = new Thread(this); runner.start() } } public void run(){ } }

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  • Java style FOR loop in a clojure interpeter ?

    - by Kevin
    I have a basic interpreter in clojure. Now i need to implement for (initialisation; finish-test; loop-update) { statements } inside my interpreter. I will attach my interpreter code I got so far. Any help is appreciated. Interpreter (declare interpret make-env) ;; (def do-trace false) ;; ;; simple utilities (def third ; return third item in a list (fn [a-list] (second (rest a-list)))) (def fourth ; return fourth item in a list (fn [a-list] (third (rest a-list)))) (def run ; make it easy to test the interpreter (fn [e] (println "Processing: " e) (println "=> " (interpret e (make-env))))) ;; for the environment (def make-env (fn [] '())) (def add-var (fn [env var val] (cons (list var val) env))) (def lookup-var (fn [env var] (cond (empty? env) 'error (= (first (first env)) var) (second (first env)) :else (lookup-var (rest env) var)))) ;; -- define numbers (def is-number? (fn [expn] (number? expn))) (def interpret-number (fn [expn env] expn)) ;; -- define symbols (def is-symbol? (fn [expn] (symbol? expn))) (def interpret-symbol (fn [expn env] (lookup-var env expn))) ;; -- define boolean (def is-boolean? (fn [expn] (or (= expn 'true) (= expn 'false)))) (def interpret-boolean (fn [expn env] expn)) ;; -- define functions (def is-function? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'lambda (first expn))))) (def interpret-function (fn [expn env] expn)) ;; -- define addition (def is-plus? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '+ (first expn))))) (def interpret-plus (fn [expn env] (+ (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define subtraction (def is-minus? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '- (first expn))))) (def interpret-minus (fn [expn env] (- (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define multiplication (def is-times? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '* (first expn))))) (def interpret-times (fn [expn env] (* (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define division (def is-divides? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '/ (first expn))))) (def interpret-divides (fn [expn env] (/ (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define equals test (def is-equals? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '= (first expn))))) (def interpret-equals (fn [expn env] (= (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define greater-than test (def is-greater-than? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '> (first expn))))) (def interpret-greater-than (fn [expn env] (> (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define not (def is-not? (fn [expn] (and (list? expn) (= 2 (count expn)) (= 'not (first expn))))) (def interpret-not (fn [expn env] (not (interpret (second expn) env)))) ;; -- define or (def is-or? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'or (first expn))))) (def interpret-or (fn [expn env] (or (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define and (def is-and? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'and (first expn))))) (def interpret-and (fn [expn env] (and (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define with (def is-with? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'with (first expn))))) (def interpret-with (fn [expn env] (interpret (third expn) (add-var env (first (second expn)) (interpret (second (second expn)) env))))) ;; -- define if (def is-if? (fn [expn] (and (list? expn) (= 4 (count expn)) (= 'if (first expn))))) (def interpret-if (fn [expn env] (cond (interpret (second expn) env) (interpret (third expn) env) :else (interpret (fourth expn) env)))) ;; -- define function-application (def is-function-application? (fn [expn env] (and (list? expn) (= 2 (count expn)) (is-function? (interpret (first expn) env))))) (def interpret-function-application (fn [expn env] (let [function (interpret (first expn) env)] (interpret (third function) (add-var env (first (second function)) (interpret (second expn) env)))))) ;; the interpreter itself (def interpret (fn [expn env] (cond do-trace (println "Interpret is processing: " expn)) (cond ; basic values (is-number? expn) (interpret-number expn env) (is-symbol? expn) (interpret-symbol expn env) (is-boolean? expn) (interpret-boolean expn env) (is-function? expn) (interpret-function expn env) ; built-in functions (is-plus? expn) (interpret-plus expn env) (is-minus? expn) (interpret-minus expn env) (is-times? expn) (interpret-times expn env) (is-divides? expn) (interpret-divides expn env) (is-equals? expn) (interpret-equals expn env) (is-greater-than? expn) (interpret-greater-than expn env) (is-not? expn) (interpret-not expn env) (is-or? expn) (interpret-or expn env) (is-and? expn) (interpret-and expn env) ; special syntax (is-with? expn) (interpret-with expn env) (is-if? expn) (interpret-if expn env) ; functions (is-function-application? expn env) (interpret-function-application expn env) :else 'error)))

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  • Mimic an HTTPRequest and HTTPResponse object in Java

    - by Ankur
    How do I mimic an HTTPServletRequest and HTTPServletResponse object. The reason is I want to test the behaviour of some servlets. I know JUnit probably provides this functionality but I don't know how to use it (I will learn soon) and need to do this reasonably quickly. HTTPServletRequest and HTTPServletResponse are both interfaces so they can't be instantiated. There is a HttpServletRequestWrapper which implements HttpServletRequest but it doesn't seem to have any setParameter() type methods and HttpServletResponse doesn't seem to have any implementing classes at all. How can I test my code by passing a suitable HttpServletRequest object and then checking that the received HttpServletResponse object matches what I expect?

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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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  • 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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  • 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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  • 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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  • 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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  • 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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  • Java Inheritance - Getting a Parameter from Parent Class

    - by Aaron
    I'm trying to take one parameter from the parent class of Car and add it to my array (carsParked), how can i do this? Parent Class public class Car { protected String regNo; //Car registration number protected String owner; //Name of the owner protected String carColor; /** Creates a Car object * @param rNo - registration number * @param own - name of the owner **/ public Car (String rNo, String own, String carColour) { regNo = rNo; owner = own; carColor = carColour; } /** @return The car registration number **/ public String getRegNo() { return regNo; } /** @return A String representation of the car details **/ public String getAsString() { return "Car: " + regNo + "\nColor: " + carColor; } public String getColor() { return carColor; } } Child Class public class Carpark extends Car { private String location; // Location of the Car Park private int capacity; // Capacity of the Car Park - how many cars it can hold private int carsIn; // Number of cars currently in the Car Park private String[] carsParked; /** Constructor for Carparks * @param loc - the Location of the Carpark * @param cap - the Capacity of the Carpark */ public Carpark (String locations, int room) { location = locations; capacity = room; } /** Records entry of a car into the car park */ public void driveIn() { carsIn = carsIn + 1; } /** Records the departure of a car from the car park */ public void driveOut() { carsIn = carsIn - 1; } /** Returns a String representation of information about the carpark */ public String getAsString() { return location + "\nCapacity: " + capacity + " Currently parked: " + carsIn + "\n*************************\n"; } }

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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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  • 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" 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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  • 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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  • 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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  • 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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