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  • What's an effective way to reuse ArrayLists in a for loop?

    - by Patrick
    hi, I'm reusing the same ArrayList in a for loop, and I use for loop results = new ArrayList<Integer>(); experts = new ArrayList<Integer>(); output = new ArrayList<String>(); .... to create new ones. I guess this is wrong, because I'm allocating new memory. Is this correct ? If yes, how can I empty them ? Added: another example I'm creating new variables each time I call this method. Is this good practice ? I mean to create new precision, relevantFound.. etc ? Or should I declare them in my class, outside the method to not allocate more and more memory ? public static void computeMAP(ArrayList<Integer> results, ArrayList<Integer> experts) { //compute MAP double precision = 0; int relevantFound = 0; double sumprecision = 0; thanks

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  • How to invoke a Servlet (doGet) in a web application on startup?

    - by Dan
    I need to invoke a Servlet on application startup since it contains some application initialization logic. I know I can set load-on-startup configuration, but this will only invoke Servlet’s init method. I need to invoke a doGet method and pass some Url parameters to it. Servlet doGet method expects ServletRequest and ServletResponse objects. Also, since this is clustered application, I need to know exactly what node I am accessing (since one option is just to open a socket and invoke a Servlet). What is the best option to perform this?

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  • How do I pause main() until all other threads have died?

    - by thechiman
    In my program, I am creating several threads in the main() method. The last line in the main method is a call to System.out.println(), which I don't want to call until all the threads have died. I have tried calling Thread.join() on each thread however that blocks each thread so that they execute sequentially instead of in parallel. Is there a way to block the main() thread until all other threads have finished executing? Here is the relevant part of my code: public static void main(String[] args) { //some other initialization code //Make array of Thread objects Thread[] racecars = new Thread[numberOfRaceCars]; //Fill array with RaceCar objects for(int i=0; i<numberOfRaceCars; i++) { racecars[i] = new RaceCar(laps, args[i]); } //Call start() on each Thread for(int i=0; i<numberOfRaceCars; i++) { racecars[i].start(); try { racecars[i].join(); //This is where I tried to using join() //It just blocks all other threads until the current //thread finishes. } catch(InterruptedException e) { e.printStackTrace(); } } //This is the line I want to execute after all other Threads have finished System.out.println("It's Over!"); } Thanks for the help guys! Eric

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  • removing comma from string array

    - by sarah
    Hi, I want to execute a query like select ID from "xyz_DB"."test" where user in ('a','b') so the corresponding code is like String s="("; for(String user:selUsers){ s+= " ' " + user + " ', "; } s+=")"; Select ID from test where userId in s; The following code is forming the value of s as ('a','b',) i want to remove the comma after the end of array how to do this ?

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  • Print the page from mozswing

    - by uhsp
    Hi, I want to add a print option to the mozswing so I can print the page from it. I've used the MozillaAutomation.renderToImage() to get the image and then print it but it does not give me what I'm looking for. Can anyone please tell me how to do it. Thanks, uhs

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  • Some pro regular expressions help needed here

    - by Camran
    I need a special regular expression, have no experience in them whatsoever so I am turning to you guys on this one: I need to validate a classifieds title field so it doesn't have any special characters in it, almost. Only letters and numbers should be allowed, and also the swedish three letters å, ä, ö, and also not case sensitive. Besides the above, these should also be allowed: The "&" sign. Parenthesis sign "()" Mathematical signs "-", "+", "%", "/", "*" Dollar and Euro signs Accent sign or whatever it's called, for example in "coupé" the apostrophe above the "e". Double quote and singel quote signs. The comma "," and point "." signs Thanks

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  • HashMap.containsValue - What's the point?

    - by Frederik
    I've got a HashMap and I need to fetch an item by its integer value. I notice there's a containsValue() function, but it would appear I still have to iterate through the map to find the correct index anyway. My question is; why use containsValue() if I'm required to traverse it afterwards? Also, am I missing the point completely? ;-)

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  • Are hashCodes unique for Strings?

    - by Batty
    Recently, I came across a piece of code, where Map<Integer, String> is used, where Integer(key) is hashCode of some string and String value corresponding to that. Is this right thing to do? Because now, equals will not be called for the String when calling get. (get is also done using hashCode() method on String object. Or, hashCode(s) are unique for unique Strings? I checked equals od String class. There is logic written for that. I am confused.

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  • Reference and Value confusion

    - by rgamber
    Hi I read this question on Stack overflow, and tried to do an example. I had the below code: public static void main(String[] args){ int i = 5; Integer I = new Integer(5); increasePrimitive(i); increaseObject(I); System.out.println(i); //Prints 5 - correct System.out.println(I); //Still prints 5 System.out.println(increaseObject2(I)); //Still prints 5 } public static void increasePrimitive(int n){ n++; } public static void increaseObject(Integer n){ n++; } public static int increaseObject2(Integer n){ return n++; } Does the increaseObject print 5 because the value of reference is changing inside that function? Am I right? I am confused why the increasedObject2 prints 5 and not 6. Can anyone please explain?

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  • Why is this removing all elements from my LinkedList?

    - by Brian
    Why is my remove method removing every element from my Doubly Linked List? If I take out that if/else statements then I can successfully remove middle elements, but elements at the head or tail of the list still remain. However, I added the if/else statements to take care of elements at the head and tail, unfortunately this method now removes every element in my list. What am I do wrong? public void remove(int n) { LinkEntry<E> remove_this = new LinkEntry<E>(); //if nothing comes before remove_this, set the head to equal the element after remove_this if (remove_this.previous == null) head = remove_this.next; //otherwise set the element before remove_this equal to the element after remove_this else remove_this.previous.next = remove_this.next; //if nothing comes after remove_this, set the tail equal to the element before remove_this if (remove_this.next == null) tail = remove_this.previous; //otherwise set the next element's previous pointer to the element before remove_this else remove_this.next.previous = remove_this.previous; //if remove_this is located in the middle of the list, enter this loop until it is //found, then remove it, closing the gap afterwards. int i = 0; for (remove_this = head; remove_this != null; remove_this = remove_this.next) { //if i == n, stop and delete 'remove_this' from the list if (i == n) { //set the previous element's next to the element that comes after remove_this remove_this.previous.next = remove_this.next; //set the element after remove_this' previous pointer to the element before remove_this remove_this.next.previous = remove_this.previous; break; } //if i != n, keep iterating through the list i++; } }

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  • How to sort an array by (smallest, largest, second smallest, second, largest) etc?

    - by Binka
    Any ideas? I can sort an array. But not in this pattern? It needs to sort by the pattern I mentioned above. public void wackySort2(int[] nums) { int sign = 0; int temp = 0; int temp2 = 0; for (int i = 0; i < nums.length; i++) { for (int j = 0; j < nums.length - 1; j++) { if (nums[j] > nums[j + 1]) { temp = nums[j]; nums[j] = nums[j + 1]; nums[j + 1] = temp; //sign = 1; System.out.println("Something has been done"); } } } }

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  • How do I make dynamic windows in Swing?

    - by Roman
    I have a general question. I would like to have a window containing some buttons, radio buttons, text fields and so on. So, user can do something (write text, select options and press buttons). As the result of the user activity window should change it structure/appearance some element should disappear and some appear. How do I program such "updates"? Should I close an old window and open a new one or I can modify content of window without closing it?

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  • How to create a datastore.Text object out of an array of dynamically created Strings?

    - by Adrogans
    I am creating a Google App Engine server for a project where I receive a large quantity of data via an HTTP POST request. The data is separated into lines, with 200 characters per line. The number of lines can go into the hundreds, so 10's of thousands of characters total. What I want to do is concatenate all of those lines into a single Text object, since Strings have a maximum length of 500 characters but the Text object can be as large as 1MB. Here is what I thought of so far: public void doPost(HttpServletRequest req, HttpServletResponse resp) { ... String[] audioSampleData = new String[numberOfLines]; for (int i = 0; i < numberOfLines; i++) { audioSampleData[i] = req.getReader().readLine(); } com.google.appengine.api.datastore.Text textAudioSampleData = new Text(audioSampleData[0] + audioSampleData[1] + ...); ... } But as you can see, I don't know how to do this without knowing the number of lines before-hand. Is there a way for me to iterate through the String indexes within the Text constructor? I can't seem to find anything on that. Of note is that the Text object can't be modified after being created, and it must have a String as parameter for the constructor. (Documentation here) Is there any way to this? I need all of the data in the String array in one Text object. Many Thanks!

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  • Why I cannot call setSomething()?

    - by badgirl
    Hello. I dont know how to acces my method of my class ProjectNode, that is returned from ExplorerManager mgr like this: mgr.getRootContext().setSomething() getRootContext() returns Node object, but I put class ProjectNode (extends AbstractNode, abstractNode extends Node)into rootContext. The compiler does not want to eat that line of code. But it must!

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  • if i call an interface method will it get the method body from implementation class and execute ?

    - by sij
    please forgive me if i am wrong: I have an interface Interface1 I have its implementation Imple implements Interface (all methods hav been implemented :) ) now consider a third class CheckCall can I do a call in the class CheckCall like I mention below Interface1 interface1; interface1.method(); all necessary imports have been done. Please tell me is it possible or not , if not then ok and if yes then tell me what will happen if i have more than one impl classes for the same interface and i am doing the same call.

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  • When should I define an hash code function for my types?

    - by devoured elysium
    Is there any other reason for implementing an hash code function for my types other than allowing for good use of hash tables? Let's say I am designing some types that I intend to use internally. I know that types are "internal" to the system, and I also know I will never use those types in hash tables. In spite of this, I decide I will have to redefine the equals() method. Theory says I should also redefine the hash code method, but I can't see any reason why, in this case, I should do it. Can anyone point me out any other reason? This question can be rephrased to : in which situations should we implement a hash code method in our types. PS : I am not asking how to implement one. I am asking when.

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