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  • Many-to-Many Relationship (with properties) in Google App Engine for Java

    - by rvandervort
    I understand from the official documentation on unowned relationships that the app must use sets of Key objects on either side of the relationship. This makes perfect sense. Coming from many years of RDBM-style programming, though, I'm pretty confused about how I can model properties of that relationship itself. For example, if I have entities Category and Entry in my many-to-many relationship and would like to persist a dateAdded property, or some other data that are only relevant when both sides of the relationship are known. I suppose it would be possible to create a third class : CategoryEntry that links the two, but this seems like a kludge. What is the proposed way to model this kind of situation ?

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  • Sequence of the Events in Java

    - by ozlegolas
    Hi, I have two events for two seperate components, but there is a problem. JTabbedPane's stateChanged event is fired before JFormattedField's focusLost event. Is there a way of making stateChange event to be fired after focusLost event. Thanks, Tuna

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  • Returning string in java using 3 parameters

    - by user2905118
    Need to write a method describePerson() that takes 3 parameters, a String giving a person’s name, a boolean indicating their gender (true for female, false for male), and an integer giving their age. The method should return a String formatted as in the following examples: Lark is female. She is 2 years old. Or Jay is male. He is 1 year old. I am not sure how to write it correctly (my code): int describePerson(String name, boolean gender, int age) { String words=""; if(gender==true) return (name + "is "+gender+". "+"She is"+age+ "years old.); else return (name + "is "+gender+". "+"She is"+age+ "years old.); } The outcome "year" and "years" is also differs, but i don't know how to make it correct..

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  • directory traversal in Java using different regular and enhanced for loops

    - by user3245621
    I have this code to print out all directories and files. I tried to use recursive method call in for loop. With enhanced for loop, the code prints out all the directories and files correctly. But with regular for loop, the code does not work. I am puzzled by the difference between regular and enhanced for loops. public class FileCopy { private File[] childFiles = null; public static void main(String[] args) { FileCopy fileCopy = new FileCopy(); File srcFile = new File("c:\\temp"); fileCopy.copyTree(srcFile); } public void copyTree(File file){ if(file.isDirectory()){ System.out.println(file + " is a directory. "); childFiles = file.listFiles(); /*for(int j=0; j<childFiles.length; j++){ copyTree(childFiles[j]); } This part is not working*/ for(File a: childFiles){ copyTree(a); } return; } else{ System.out.println(file + " is a file. "); return; } } }

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  • Container of Generic Types in java

    - by Cyker
    I have a generic class Foo<T> and parameterized types Foo<String> and Foo<Integer>. Now I want to put different parameterized types into a single ArrayList. What is the correct way of doing this? Candidate 1: public class MMM { public static void main(String[] args) { Foo<String> fooString = new Foo<String>(); Foo<Integer> fooInteger = new Foo<Integer>(); ArrayList<Foo<?> > list = new ArrayList<Foo<?> >(); list.add(fooString); list.add(fooInteger); for (Foo<?> foo : list) { // Do something on foo. } } } class Foo<T> {} Candidate 2: public class MMM { public static void main(String[] args) { Foo<String> fooString = new Foo<String>(); Foo<Integer> fooInteger = new Foo<Integer>(); ArrayList<Foo> list = new ArrayList<Foo>(); list.add(fooString); list.add(fooInteger); for (Foo foo : list) { // Do something on foo. } } } class Foo<T> {} In a word, it is related to the difference between Foo<?> and the raw type Foo. Update: Grep What is the difference between the unbounded wildcard parameterized type and the raw type? on this link may be helpful.

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  • Rotation in a Vector2d class in Java

    - by wanstein
    I've been working on this for one hour, just can't get it. I have a Vector2d class: public class Vector2d { public double x = 0.0; public double y = 0.0; .... } This vector class has a rotate() method which is causing me trouble. The first snippet seems to make the x and y values smaller and smaller. The second one works just fine! Am I missing something simple here? public void rotate(double n) { this.x = (this.x * Math.cos(n)) - (this.y * Math.sin(n)); this.y = (this.x * Math.sin(n)) + (this.y * Math.cos(n)); } This works: public void rotate(double n) { rx = (this.x * Math.cos(n)) - (this.y * Math.sin(n)); ry = (this.x * Math.sin(n)) + (this.y * Math.cos(n)); x = rx; y = ry; } I just can't spot any difference there

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  • Java - multithreaded access to a local value store which is periodically cleared

    - by Telax
    I'm hoping for some advice or suggestions on how best to handle multi threaded access to a value store. My local value storage is designed to hold onto objects which are currently in use. If the object is not in use then it is removed from the store. A value is pumped into my store via thread1, its entry into the store is announced to listeners, and the value is stored. Values coming in on thread1 will either be totally new values or updates for existing values. A timer is used to periodically remove any value from the store which is not currently in use and so all that remains of this value is its ID held locally by an intermediary. Now, an active element on thread2 may wake up and try to access a set of values by passing a set of value IDs which it knows about. Some values will be stored already (great) and some may not (sadface). Those values which are not already stored will be retrieved from an external source. My main issue is that items which have not already been stored and are currently being queried for may arrive in on thread1 before the query is complete. I'd like to try and avoid locking access to the store whilst a query is being made as it may take some time.

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  • java/swing: font size selection + rendering

    - by Jason S
    I want to create and fill/stroke a path that consists of an outer boundary which is a square of side d and an inner boundary that is the outline of any of the capital letters. How can I do this? (challenges = creating a mask from a font, and figuring out the right size/position to use)

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  • Java scanner - taking specific part of line

    - by user1290213
    Hi ive got a log file containing trace routes and pings. Ive seperated these by using if(scanner.nextLine().startsWith("64 bytes"){} so i can work with just the pings for now. All im interested in from the ping is time=XX example data line = 64 bytes from ziva.zarnet.ac.zw (209.88.89.132): icmp_seq=119 ttl=46 time=199 ms I have been reading other peoples similar questions and im not sure how to apply to mine. I literally need just the number as i will be putting them into a csv file so i can make a graph of the data.

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  • question about timestamp with timezone in postgresql+java?

    - by ylazez
    hey guys i have a column in the database(postgresql) i want to insert the current time in GMT in this column when getting the current time and inserting it into the DB it's inserted in the server timezone GMT-5 although that time was in GMT+0 any ideas how to insert this time in the database in GMT timezone ?

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  • java random percentages

    - by erw
    I need to generate n percentages (integers between 0 and 100) such that the sum of all n numbers adds up to 100. If I just do nextInt() n times, each time ensuring that the parameter is 100 minus the previously accumulated sum, then my percentages are biased (i.e. the first generated number will usually be largest etc.). How do I do this in an unbiased way?

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  • Parsing query strings in Java

    - by Will
    J2EE has ServletRequest.getParameterValues(). On non-EE platforms, URL.getQuery() simply returns a string. What's the normal way to properly parse the query string in a URL when not on J2EE?

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  • Time not entered in mysql ? Java

    - by Nitesh Panchal
    Hello, I have a datetime field in mysql table and i am using JPA for persisting data but only date goes in database. Time always shows 00:00:00. What should i do? I am not doing any manipulation with Date. All i do is to assign new Date() to a variable and store it in database. What am i doing wrong?

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  • Java iterative vs recursive

    - by user1389813
    Can anyone explain why the following recursive method is faster than the iterative one (Both are doing it string concatenation) ? Isn't the iterative approach suppose to beat up the recursive one ? plus each recursive call adds a new layer on top of the stack which can be very space inefficient. private static void string_concat(StringBuilder sb, int count){ if(count >= 9999) return; string_concat(sb.append(count), count+1); } public static void main(String [] arg){ long s = System.currentTimeMillis(); StringBuilder sb = new StringBuilder(); for(int i = 0; i < 9999; i++){ sb.append(i); } System.out.println(System.currentTimeMillis()-s); s = System.currentTimeMillis(); string_concat(new StringBuilder(),0); System.out.println(System.currentTimeMillis()-s); } I ran the program multiple time, and the recursive one always ends up 3-4 times faster than the iterative one. What could be the main reason there that is causing the iterative one slower ?

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  • Java ThreadPool for multiple identical tasks

    - by tdimmig
    I have 1 thread who sole job is to grab DatagramPackets off of a socket and stick them in a buffer. Another thread works out of that buffer, processing the DatagramPackets. I'd like to have a pool of threads working out of that buffer. I had thought to use a fixed thread pool to do this. To do so, do I need to create the pool, then submit enough runnables for execution to fill it up? I had hoped for a way to say "this is the thread/runnable that I want you to execute, this is how many I want running, GO!". Is there such a method of doing this? Is something other than a fixed thread pool better suited?

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  • pls give reason why this java program always comes to the else part

    - by Anbu
    public class Test { public static void main(String[] args){ if (5.0 5) // (5.0<5) for both case it is going to else System.out.println("5.0 is greater than 5"); else System.out.println("else part always comes here"); /another sample/ if (5.0 == 5) System.out.println("equals"); else System.out.println("not equal"); } } can any one explain the first "if statement" why it always come to else part

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  • Executing in java code an external program that takes arguments

    - by rmaster
    Process p; String line; String path; String[] params = new String [3]; params[0] = "D:\\prog.exe"; params[1] = picA+".jpg"; params[2] = picB+".jpg"; try { p = Runtime.getRuntime().exec(params); BufferedReader input = new BufferedReader (new InputStreamReader(p.getInputStream())); while ((line = input.readLine()) != null) System.out.println(line); input.close(); } catch (IOException e) {System.out.println(" procccess not read"+e);} i don't get any error, just nothing in cmd.exe prog.exe is working fine What to improve in order to make this code working?

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  • Pass off execution to different/specific thread in Java

    - by Mike
    I have about 4 threads. One thread keeps checking some data that the other thread is updating. The others are doing some processing in the background. All have been started at this point. My question is when the checking thread sees that the data has not been updated yet I currently sleep for a little bit but is there any way for me to tell the system to back to executing the thread that does the updating? That or is there any way I can put something like a listener on the data(a String) and once its updated an event will fire that will do what it needs to do? I tried using yield() and it seemed to just keep returning to the thread I called yield() from. Thanks

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  • Constructors from extended class in Java

    - by Crystal
    I'm having some trouble with a hw assignment. In one assignment, we had to create a Person class. Mine was: public class Person { String firstName; String lastName; String telephone; String email; public Person() { firstName = ""; lastName = ""; telephone = ""; email = ""; } public Person(String firstName) { this.firstName = firstName; } public Person(String firstName, String lastName, String telephone, String email) { this.firstName = firstName; this.lastName = lastName; this.telephone = telephone; this.email = email; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } public String getTelephone() { return telephone; } public void setTelephone(String telephone) { this.telephone = telephone; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } public boolean equals(Object otherObject) { // a quick test to see if the objects are identical if (this == otherObject) { return true; } // must return false if the explicit parameter is null if (otherObject == null) { return false; } if (!(otherObject instanceof Person)) { return false; } Person other = (Person) otherObject; return firstName.equals(other.firstName) && lastName.equals(other.lastName) && telephone.equals(other.telephone) && email.equals(other.email); } public int hashCode() { return 7 * firstName.hashCode() + 11 * lastName.hashCode() + 13 * telephone.hashCode() + 15 * email.hashCode(); } public String toString() { return getClass().getName() + "[firstName = " + firstName + '\n' + "lastName = " + lastName + '\n' + "telephone = " + telephone + '\n' + "email = " + email + "]"; } } Now we have to extend that class and use that class in our constructor. The function protoype is: public CarLoan(Person client, double vehiclePrice, double downPayment, double salesTax, double interestRate, CAR_LOAN_TERMS length) I'm confused on how I use the Person constructor from the superclass. I cannot necessarily do super(client); in my constructor which is what the book did with some primitive types in their example. Not sure what the correct thing to do is... Any thoughts? Thanks!

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  • [Processing/Java]Visibility/Layering Issue

    - by nnash
    I'm working on a small sketch in processing where I am making a "clock" using the time functions and drawing ellipses across the canvas based on milliseconds, seconds and minutes. I'm using a for loop to draw all of the ellipses and each for loop is inside its own method. I'm calling each of these methods in the draw function. However for some reason only the first method that is called is being drawn, when ideally I would like to have them all being visibly rendered. //setup program void setup() { size(800, 600); frameRate(30); background(#eeeeee); smooth(); } void draw(){ milliParticles(); secParticles(); minParticles(); } //time based particles void milliParticles(){ for(int i = int(millis()); i >= 0; i++) { ellipse(random(800), random(600), 5, 5 ); fill(255); } } void secParticles() { for(int i = int(second()); i >= 0; i++) { fill(0); ellipse(random(800), random(600), 10, 10 ); background(#eeeeee); } } void minParticles(){ for(int i = int(minute()); i >= 0; i++) { fill(50); ellipse(random(800), random(600), 20, 20 ); } }

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  • Catching TransactionRolledbackLocalException in Java

    - by user271858
    I receive javax.ejb.TransactionRolledbackLocalException in Websphere 7 from the container and I wonder how is it possible to catch this exception? I have a timeout set in Websphere and get this message after this time. I run session beans. I am trying to find what SQl statement was the cause of this exception. Where can i find that?

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  • Example applications and benefits of using "C" , "C++" or "Java"

    - by Waltzy
    Ok, I'm revising for my upcoming year 2 exams on a CS course and its likely something like this will come up. my question is what is an ideal application that would especially benefit from the program features of each of the three languages? I have a vague idea but getting a second opinion could really help. JavaPortability, easy - good for GUIs. C++Fast but may requite significant changes in order to be moved from system to system, good for image processing. CI'm unsure here small embedded applications? Some clarification on this would be really appreciated, thanks again StackOverflow

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