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  • Explicit constructor still has default values even though a default constructor is not invoked.

    - by Phoenix
    According to my understanding a default constructor initializes the state of the object to default values, so if i provide an explicit no-arg public constructor like this then how are the values of d and e still getting initialized to zero because in this case the default constructor is not invoked. public class B extends A{ private int d; private int e; public B() { System.out.println(d); System.out.println(e); } } EDIT:: The only thing default constructor does is call to super() then how come if i have a explicitly mentioned a constructor here and A has a protected variable say c which is initialized to 17 in its constructor. Should I not be explicitly calling super() to be able to see that change since I'm using my own constructor ? Why is B still getting the value of 17 through inheritance ?

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  • one more time about loop that doesn't work

    - by unit
    I have asked a couple of questions about this for loop: String[] book = new String [ISBN_NUM]; bookNum.replaceAll("-",""); if (bookNum.length()!=ISBN_NUM) throw new ISBNException ("ISBN "+ bookNum + " must be 10 characters"); for (int i=0;i<bookNum.length();i++) { if (Character.isDigit(bookNum.charAt(i))) book[j]=bookNum.charAt(i); //this is the problem right here j++; if (book[9].isNotDigit()|| book[9]!="x" || book[9]!="X") throw new ISBNException ("ISBN " + bookNum + " must contain all digits" + "or 'X' in the last position"); } which will not compile. An answer I had from the other question I asked told me that the line where the error occurs is wrong in that bookNum.charAt(i) is an (immutable) string, and I can't get the values into a book array that way. What I need to do on my assignment is check an ISBN number (bookNum) to see that it is all numbers, except the last digit can be an 'x' (valid ISBN). Is this the best way to do it? If so, what the hell am I doing wrong? If not, what method would be a better one to use?

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  • Vertical line on HxW canvas of pixels

    - by bobby williams
    I searched and found nothing. I'm trying to draw lines (simple y=mx+b ones) on a canvas of black pixels. It works fine, but no line occurs when it is vertical. I'm not sure why. My first if statement checks if the denominator is zero, therefore m is undefined and no need for a line equation. My second and third if statement check how steep it is and based on that, calculate the points in between. I don't think there is a need for other classes, since I think there is a bug in my code or I'm just not translating the mathematics into code properly. If more is needed, I'll be happy to post more. /** * Returns an collection of points that connects p1 and p2 */ public ArrayList getPoints() { ArrayList points = new ArrayList(); // checks to see if denominator in m is zero. if zero, undefined. if ((p2.getX() - p1.getX()) == 0) { for (int y = p1.getY(); y<p2.getY(); y++) { points.add(new Point(p1.getX(), y, getColor())); } } double m = (double)(p2.getY()-p1.getY())/(double)(p2.getX()-p1.getX()); int b = (int)(p1.getY() - (m * p1.getX())); // checks to see if slope is steep. if (m > -1 || m < 1) { for (int x = p1.getX(); x<p2.getX(); x++) { int y = (int) ((m*x)+b); points.add(new Point(x, y, getColor())); } } // checks to see if slope is not steep. if (m <= -1 || m >= 1) { for (int y = p1.getY(); y<p2.getY(); y++) { int x = (int) ((y-b)/m); points.add(new Point(x, y, getColor())); } } return points; }

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  • How can I use one stream and save result to many places?

    - by plasticrabbit
    I using servlet and Apache ServletFileUpload that provides stream to uploaded image. All I want to do is to store that image to db and also store resized (I using JAI) version to db. How can I achieve this without saving image to drive. As I understand stream can be read only once. So I need to store whole image in memory? Is it expensive for performance? Or there are another way?

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  • JNI - native method with ByteBuffer parameter

    - by Ajan
    I've got a method: public native void doSomething(ByteBuffer in, ByteBuffer out); Generated by javah C/C++ header of this method is: JNIEXPORT void JNICALL Java__MyClass_doSomething (JNIEnv *, jobject, jobject, jobject, jint, jint); How can I get a data array from jobject (that is a ByteBuffer instance) ?

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  • Is my way of doing threads in Android correct?

    - by Charlie
    Hi, I'm writing a live wallpaper, and I'm forking off two separate threads in my main wallpaper service. One updates, and the other draws. I was under the impression that once you call thread.start(), it took care of everything for you, but after some trial and error, it seems that if I want my update and draw threads to keep running, I have to manually keep calling their run() methods? In other words, instead of calling start() on both threads and forgetting, I have to manually set up a delayed handler event that calls thread.run() on both the update and draw threads every 16 milliseconds. Is this the correct way of having a long running thread? Also, to kill threads, I'm just setting them to be daemons, then nulling them out. Is this method ok? Most examples I see use some sort of join() / interrupt() in a while loop...I don't understand that one...

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  • How to close IOs?

    - by blackdog
    when i managed IO, i found a problem. i used to close it like this: try { // my code } catch (Exception e) { // my code } finally{ if (is != null) { is.close(); } } but the close method also would throw exception. if i have more than one IO, i have to close all of them. so the code maybe like this: try { // my code } catch (Exception e) { // my code } finally{ if (is1 != null) { is1.close(); } if(is2 != null{ is2.close(); } // many IOs } if is1.close() throws an exception, is2, is3 would not close itself. So i have to type many try-catch-finally to control them. is there other way to solve the problem?

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  • What's the reason behind the jumping GeneratedValue(strategy=GenerationType.TABLE) when not specifyi

    - by joeduardo
    Why do I need to add allocationSize=1 when using the @TableGenerator to ensure that the id wouldn't jump from 1, 2,... to 32,xxx, 65,xxx,... after a jvm restart? Is there a design reason for the need to specify the allocationSize? This snippet would produce the jumping ids @Id @GeneratedValue(strategy = GenerationType.TABLE) private Long id; Here's the modified snippet that produces the properly sequenced ids @Id @GeneratedValue(strategy = GenerationType.TABLE, generator = "account_generator") @TableGenerator(name = "account_generator", initialValue = 1, allocationSize = 1) private Long id;

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  • Servlet File Upload Memory Consumption

    - by Scott
    Hi, I'm using a servlet to do a multi fileupload (using apache commons fileupload to help). A portion of my code is posted below. My problem is that if I upload several files at once, the memory consumption of the app server jumps rather drastically. This is probably OK if it were only until the file upload is finished, but the app server seems to hang on to the memory and never return it to the OS. I'm worried that when I put this into production I'll end up getting an out of memory exception on the server. Any ideas on why this is happening? I'm thinking the server may have started a session and will give the memory back after it expires, but I'm not 100% positive. if(ServletFileUpload.isMultipartContent(request)) { ServletFileUpload upload = new ServletFileUpload(); FileItemIterator iter = upload.getItemIterator(request); while(iter.hasNext()) { FileItemStream license = iter.next(); if(license.getFieldName().equals("upload_button") || license.getName().equals("")) continue; //DataInputStream stream = new DataInputStream(license.openStream()); InputStream stream = license.openStream(); ArrayList<Integer> byteArray = new ArrayList<Integer>(); int tempByte; do { tempByte = stream.read(); byteArray.add(tempByte); }while(tempByte != -1); stream.close(); byteArray.remove(byteArray.size()-1); byte[] bytes = new byte[byteArray.size()]; int i = 0; for(Integer tByte : byteArray) { bytes[i++] = tByte.byteValue(); } Thanks in advanced!!

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  • How can find out the system default currency symbol on BlackBerry?

    - by ageektrapped
    I have a need to display a currency value in my application. There doesn't seem to be an easy way to do this with the RIM API, so I'm reduced to creating my own solution (a common refrain for BlackBerry development, unfortunately) Currently I'm using the Formatter class, from javax.microedition.locale like so protected String formatResult(double result) { try { Locale l = Locale.getDefaultForSystem(); Formatter formatter = new Formatter(l.toString()); return formatter.formatCurrency(result); } catch (UnsupportedLocaleException e) { return "This fails for the default locale because BlackBerry sucks"; } } I always hit the catch block in the simulator. Since this doesn't work by default on the simulator, I'm hesitant to put it in the application. So I have two questions: Can anyone tell me if the above solution is the way to go? And how to fix it, of course. Is there a way I can retrieve the currency symbol for the current locale programmatically so I can format myself?

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  • Validation - Data Integrity

    - by Thomas
    A table can only store 10 records in a particular state, 10 users over 30 years for example, the others must be less than 30 years. It is a business rule and as such should be respected. How to ensure that state? Think: multiple users accessing this table.

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  • How to trigger the specific controller action using a button?

    - by Eugene
    I'm creating a simple training project. I've implemented a controller method, which deletes an item from the list. The method is looking like this: @Controller @RequestMapping(value = "/topic") public class TopicController { @Autowired private TopicService service; ... @RequestMapping(value = "/deleteComment/{commentId}", method = RequestMethod.POST) public String deleteComment(@PathVariable int commentId, BindingResult result, Model model){ Comment deletedComment = commentService.findCommentByID(commentId); if (deletedComment != null) { commentService.deleteComment(deletedComment); } return "refresh:"; } } This method is called from the button-tag, which is looking in the following way: _form> _button formaction = "../deleteComment/1" formmethod = "post">delete_/button> _/form> Sorry, but in the form tag I've changed all the '<' characters with the '_', because the tag was invisible. In my project the form-tag is looking like a cliuckable button. But there is a serious problem: controller's method is never triggered. How can I trigger it, using a button-tag? P.S. the call is performed from the page with URI http://localhost:8080/simpleblog/topic/details/2 and controller's URI is the http://localhost:8080/simpleblog/topic/deleteComment/2

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  • JAXM soap message parsing

    - by Dean
    I am getting the following XML back from a .net service: <?xml version="1.0" encoding="utf-8"?> <soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <soap:Body> <validateCredentialsResponse xmlns="http://www.paragon.com/positionmonitor/PositionMonitor"> <validateCredentialsResult> <ResultData xsi:type="ValidateCredentialsResultData"> <validated>true</validated> <alreadyLoggedIn>false</alreadyLoggedIn> </ResultData> <Status> <Condition xmlns="">SUCCESS</Condition> <ErrorCode xmlns="">BO.00000</ErrorCode> <ErrorDesc xmlns="">OK</ErrorDesc> </Status> </validateCredentialsResult> </validateCredentialsResponse> </soap:Body> </soap:Envelope> ...and I'm trying to parse it using JAXM, however the following always evaluates to null: SOAPEnvelope env = reply.getSOAPPart().getEnvelope(); Can anyone help me out here?

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  • Find messages from certain key till certain key while being able to remove stale keys.

    - by Alfred
    My problem Let's say I add messages to some sort of datastructure: 1. "dude" 2. "where" 3. "is" 4. "my" 5. "car" Asking for messages from index[4,5] should return: "my","car". Next let's assume that after a while I would like to purge old messages because they aren't useful anymore and I want to save memory. Let's say at time x messages[1-3] became stale. I assume that it would be most efficient to just do the deletion once every x seconds. Next my datastructure should contain: 4. "my" 5. "car" My solution? I was thinking of using a concurrentskiplistset or concurrentskiplist map. Also I was thinking of deleting the old messages from inside a newSingleThreadScheduledExecutor. I would like to know how you would implement(efficiently/thread-safe) this or maybe use a library?

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  • Accessing variablss through a different class within the constructor of latter classes of an object

    - by Haxed
    In the code below, I've added two lines that print output. The first line prints junk as usual, but surprisingly the second one gives me a compilation error. Why? class Student { private String name; public Student(String name){ this.name = name; } public String getName(){ return name; } } class StudentServer { public StudentServer(){ Student[] s = new Student[30]; s[0] = new Student("Nick"); // LINE 01: This compiles, although prints junk System.out.println(s[0]); // LINE 02: I get a error called cannot find symbol System.out.println(s[0].getName()); } public static void main(){ new StudentServer(); } } Many Thanks

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  • So I dynamically load a jar at runtime how do I use it?

    - by justinhj
    So question 194698 shows how to load a jar file at runtime and you can load individual named classes and get a Class object. Now my problem is I want to be able to cast those Classes to the types they really are, but I can't because I can't use an import since the whole point is to load it at runtime rather than compile time. It seems like the way to go is to use reflection to discover the functions and field names, but that seems brittle since the API in the jar files could change and the code won't break until it is run. Is there a better way?

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  • Confusion with a while statement evaluating if a number is triangular

    - by Darkkurama
    I've been having troubles trying to figure out how to solve a function. I've been assigned the development of a little programme which tells if a number is "triangular" (a number is triangular when the addition of certain consecutive numbers in the [1,n] interval is n. Following the definition, the number 10 is triangular, because in the [1,10] interval, 1+2+3+4=10). I've coded this so far: class TriangularNumber{ boolean numTriangular(int n) { boolean triangular = false; int i = n; while(n>=0 && triangular){ //UE06 is a class which contains the function "f0", which makes the addition of all the numbers in a determined interval UE06 p = new UE06(); if ((p.f0(1, i))==n) triangular = true; else i=i-1; } return triangular; } boolean testTriangular = numTriangular(10) == true && numTriangular(7) == false && numTriangular(6) == true; public static void main(String[] args){ TriangularNumber p = new TriangularNumber(); System.out.println("testTriangular = " + p.testTriangular); } } According to those boolean tests I made, the function is wrong. As I see the function, it goes like this: I state that the input number in the initial state isn't triangular (triangular=false) and i=n (determining the interval [1,i] where the function is going to be evaluated While n is greater or equals 0 and the number isn't triangular, the loop starts The loop goes like this: if the addition of all the numbers in the [1,i] interval is n, the number is triangular, causing the loop to end. If that statement is false, i goes from i to (i-1), starting the loop again with that particular interval, and so on till the addition is n. I can't spot the error in my "algorithm", any advice? Thanks!

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  • Is it possible to establish default values for inherited fields in subclasses?

    - by Christian Mann
    I'm trying to establish a default value for inherited fields from superclasses. So, my class hierarchy is thus: Character - Enemy - Boss                 \                   - Hero Each Character has a public static char avatar to represent him on an ASCII playing field. How do I set a default value for the avatar of each class inherited from Character? Thank you!

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