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  • Hibernate 1:M relationship ,row order, constant values table and concurrency

    - by EugeneP
    table A and B need to have 1:M relationship a and b are added during application runtime, so A created, then say 4 B's created. Each B instance has to come in order, so that I could later extract them in the same order as I added them. The app will be a web-app running on Tomcat, so 10 instances may work simultaneously. So my question are: 1) How to preserve inserting order, so that I could extract B instances that A references in the same order as I persisted them. That's tricky, because we add to a Collection and then it gets saved (am I right?). So, it depends on how Hibernate saves it, what if it changes the order in what we added instances? I've seen something like LIST instead of SET when describing relationships, is that what I need? 2) How to add a 3-rd column to B so that I could differentiate the instances, something like SEX(M,F,U) in B table. Do I need a special table, or there's and easy way to describe constants in Hibernate. What do you recommend? 3) Talking about concurrency, what methods do you recommend to use? There should be no collisions in the db and as you see, there might easily be some if rows are not inserted (PK added) right where it is invoked without delays ?

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  • Writing a recursive sorting algorithm of an array of integers

    - by 12345
    I am trying to write a recursive sorting algorithm for an array of integers. The following codes prints to the console: 3, 5, 2, 1, 1, 2, 6, 7, 8, 10, 20 The output should be sorted but somehow "it doesn't work". public static void main(String[] args) { int[] unsortedList = {20, 3, 1, 2, 1, 2, 6, 8, 10, 5, 7}; duplexSelectionSort(unsortedList, 0, unsortedList.length-1); for (int i = 0; i < unsortedList.length; i++) { System.out.println(unsortedList[i]); } } public static void duplexSelectionSort( int[] unsortedNumbers, int startIndex, int stopIndex) { int minimumIndex = 0; int maximumIndex = 0; if (startIndex < stopIndex) { int index = 0; while (index <= stopIndex) { if (unsortedNumbers[index] < unsortedNumbers[minimumIndex]) { minimumIndex = index; } if (unsortedNumbers[index] > unsortedNumbers[maximumIndex]) { maximumIndex = index; } index++; } swapEdges(unsortedNumbers, startIndex, stopIndex, minimumIndex, maximumIndex); duplexSelectionSort(unsortedNumbers, startIndex + 1, stopIndex - 1); } } public static void swapEdges( int[] listOfIntegers, int startIndex, int stopIndex, int minimumIndex, int maximumIndex) { if ((minimumIndex == stopIndex) && (maximumIndex == startIndex)) { swap(listOfIntegers, startIndex, stopIndex); } else { if (maximumIndex == startIndex) { swap(listOfIntegers, maximumIndex, stopIndex); swap(listOfIntegers, minimumIndex, startIndex); } else { swap(listOfIntegers, minimumIndex, startIndex); swap(listOfIntegers, maximumIndex, stopIndex); } } } public static void swap(int[] listOfIntegers, int index1, int index2) { int savedElementAtIndex1 = listOfIntegers[index1]; listOfIntegers[index1] = listOfIntegers[index2]; listOfIntegers[index2] = savedElementAtIndex1; }

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  • What to prefer in the following case?

    - by GK
    say suppose I have class as : public class Age { private int age; public int getAge() { return this.age; } } In my Main class I am calling the getAge() method many times. So I wanted to know is it advisable to call so many times or call once and assign it to some variable and use that variable. Which is best and why?

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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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  • Tapestry5 display grid component using a hashmap

    - by Eldred
    Hi there I am trying to attempt to display a hashmap using a grid component. If I use List list = CollectionFactory.newList(MyHashMap) it returns a list however on my template page I see Empty and false when passing my parameter t:souce="list" to my grid component, therefore my grid component only returns one row. Some code snippets would be a great help. Many thanks

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  • A typical lifecycle of a Hibernate object in a web app - ?

    - by EugeneP
    Describe please a typical lifecycle of a Hibernate object (that maps to a db table) in a web app. Suppose, you create a new instance of an object and persist in the db. But during the app lifetime you'll be working on a detached object and finally you need to update it in the database, for example on exit. How does it look like with hibernate and spring? p.s. Can transactions and sessions live between servlet transitions? So that we opened 1 session and use it in all servlets without a need to reopen it?

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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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  • How can I improve the performance of this algorithm

    - by Justin
    // Checks whether the array contains two elements whose sum is s. // Input: A list of numbers and an integer s // Output: return True if the answer is yes, else return False public static boolean calvalue (int[] numbers, int s){ for (int i=0; i< numbers.length; i++){ for (int j=i+1; j<numbers.length;j++){ if (numbers[i] < s){ if (numbers[i]+numbers[j] == s){ return true; } } } } return false; }

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  • Ordered Data Structure that allows to efficiently remove duplicate items

    - by devoured elysium
    I need a data structure that Must be ordered (adding elements a, b and c to an empty structure, will make them be at positions 0, 1 and 2). Allows to add repeated items. This is, I can have a list with a, b, c, a, b. Allows removing all ocurrences of a given item (if I do something like delete(1), it will delete all ocurrences of 1 in the structure). I can't really pick what the best data structure could be in here. I thought at first about something like a List(the problem is having an O(n) operation when removing items), but maybe I'm missing something? What about trees/heaps? Hashtables/maps? I'll have to assume I'll do as much adding as removing with this data structure. Thanks

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  • How is this function being made use of?

    - by Kay
    Hello all, I am just studying a few classes given to me by my lecturer and I can't understand how the function heapRebuild is being made used of! It doesn't change any global variables and it doesn't print out anything ad it doesn't return anything - so should this even work? It shouldn't, should it? If you were told to make use of heapRebuild to make a new function removeMac would you edit heapRebuild? public class MaxHeap<T extends Comparable<T>> implements Heap<T>{ private T[] heap; private int lastIndex; public T removeMax(){ T rootItem = heap[0]; heap[0] = heap[lastIndex-1]; lastIndex--; heapRebuild(heap, 0, lastIndex); return rootItem; } protected void heapRebuild(T[ ] items, int root, int size){ int child = 2*root+1; if( child < size){ int rightChild = child+1; if ((rightChild < size) && (items[rightChild].compareTo(items[child]) > 0)){ child = rightChild; } if (items[root].compareTo(items[child]) < 0){ T temp = items[root]; items[root] = items[child]; items[child] = temp; heapRebuild(items, child, size);} } } }

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  • out-of-the-box way to get an idmap from hibernate for a given entity?

    - by Geert-Jan
    Over and over again I notive myself getting a list from hibernate, and the first thing next is put it in an idmap like: List<House> entities = s.createCriteria(House.class).list(); Map<String,House> entitymap = new HashMap<String,House>(); for(TA_entity e:entities){ entitymap.put(e.getId(), e); } Is there a way to get this directly out of hibenerate? afterall Hibernate is familiar with the id.

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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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  • 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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  • 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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  • Is it a good practice to have trim in setter?

    - by zibi
    I'm doing a code review and I noticed such a code: @Entity @Table(name = "SOME_TABLE") public class SomeReportClass { @Column(name = "REPORT_NUMBER", length = 6, nullable = false) private String reportNumber; ..... public String getReportNumber() { return reportNumber; } public void setReportNumber(String reportNumber) { this.reportNumber = StringUtils.trimToNull(reportNumber); } } Every time I see trimming inside of a setter I feel that its not the clearest solution - what is the general practice with that issue?

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  • Should my DAOs (Database Entities) Directly match my UI Objects?

    - by scarpacci
    I am trying to figure out best practice for N-Tier application design. When designing the objects my UI needs and those that will be persisted in the DB some of my colleagues are suggesting that the objects be one in the same. This doesn't not feel right to me and I am ultimately looking for some best practice documentation to help me in this decision. I honestly do not understand why I would want to design this way given that other applications may want to interact with my Data Access Layer....or it is just ignorance or lack of understanding on my part. Any documentation, information you could provide would be greatly appreciated. Just want to better understand these concepts and I am having a hard time finding some good information on the best practice for implementing these patterns (Or it is right in front of me on what I found and I didn't understand what was being outlined). Thanks, S

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  • Does beginTransaction in Hibernate allocate a new DB connection?

    - by illscience
    Hi folks - Just wondering if beginning a new transaction in Hibernate actually allocates a connection to the DB? I'm concerned b/c our server begins a new transaction for each request received, even if that request doesn't interact with the DB. We're seeing DB connections as a major bottleneck, so I'm wondering if I should take the time narrow the scope of my transactions. Searched everywhere and haven't been able to find a good answer. The very simple code is here: SessionFactory sessionFactory = (SessionFactory) Context.getContext().getBean("sessionFactory"); sessionFactory.getCurrentSession().beginTransaction(); sessionFactory.getCurrentSession().setFlushMode(FlushMode.AUTO); thanks very much! a

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