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  • How to use java.Set

    - by owca
    I'm trying to make it working for quite some time,but just can't seem to get it. I have object Tower built of Block's. I've already made it working using arrays, but I wanted to learn Set's. I'd like to get similar functionality to this: public class Tower { public Tower(){ } public Tower add(Block k1){ //(...) //if block already in tower, return "Block already in tower" } public Tower delete(Block k1){ //(...) //if block already dleted, show "No such block in tower" } } Someone gave me some code, but I constantly get errors when trying to use it : Set<Block> tower = new HashSet<Block>(); boolean added = tower.add( k1 ); if( added ) { System.out.println("Added 1 block."); } else { System.out.println("Tower already contains this block."); } How to implement it ?

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  • Removing duplicates without overriding hash method

    - by Javi
    Hello, I have a List which contains a list of objects and I want to remove from this list all the elements which have the same values in two of their attributes. I had though about doing something like this: List<Class1> myList; .... Set<Class1> mySet = new HashSet<Class1>(); mySet.addAll(myList); and overriding hash method in Class1 so it returns a number which depends only in the attributes I want to consider. The problem is that I need to do a different filtering in another part of the application so I can't override hash method in this way (I would need two different hash methods). What's the most efficient way of doing this filtering without overriding hash method? Thanks

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  • How to recursively serialize an object using reflection ?

    - by Tony
    I want to navigate to the N-th level of an object, and serialize it's properties in String format. For Example: class Animal { public String name; public int weight; public Animal friend; public Set<Animal> children = new HashSet<Animal>() ; } should be serialized like this: {name:"Monkey", weight:200, friend:{name:"Monkey Friend",weight:300 ,children:{...if has children}}, children:{name:"MonkeyChild1",weight:100,children:{... recursively nested}} } And you may probably notice that it is similar to serializing an object to json. I know there're many libs can do this, can you give me some instructive ideas on how to write this?

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  • Coding guidelines + Best Practices?

    - by Chathuranga Chandrasekara
    I couldn't find any question that directly applies to my query so I am posting this as a new question. If there is any existing discussion that may help me, please point it out and close the question. Question: I am going to do a presentation on C# coding guidelines but it is not supposed to limit to coding standards. So I have a rough idea but I think I need to address good programing practices. So the contents will be something like this. Basic coding standards - Casing, Formatting etc. Good practices - Usage of Hashset over other data structures, String vs String Builder, String's immutability and using them effectively etc Really I would like to add more good practices (Especially to improve the performance.) So like to hear some more good practices to be used with C#. Any suggestions??? (No need of large descriptions :) Just the idea is sufficient.)

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  • calling Overloaded method from a generic method.

    - by asela38
    How to create a generic method which can call overloaded methods? I tried but it gives a compilation error. Test.java:19: incompatible types found : java.lang.Object required: T T newt = getCloneOf(t); ^ import java.util.*; public class Test { private Object getCloneOf(Object s) { return new Object(); } private String getCloneOf(String s) { return new String(s); } private <T> Set<T> getCloneOf(Set<T> set){ Set<T> newSet = null; if( null != set) { newSet = new HashSet<T>(); for (T t : set) { T newt = getCloneOf(t); newSet.add(newt); } } } }

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  • Coding guidelines + Best Practises?

    - by Chathuranga Chandrasekara
    I couldn't find any question that directly applies to my query so I am posting this as a new question. If there is any existing discussion that may help me, please point it out and close the question. Question: I am going to do a presentation on C# coding guidelines but it is not supposed to limit to coding standards. So I have a rough idea but I think I need to address good programing practices. So the contents will be something like this. Basic coding standards - Casing, Formatting etc. Good practices - Usage of Hashset over other data structures, String vs String Builder, String's immutability and using them effectively etc Really I would like to add more good practices (Especially to improve the performance.) So like to hear some more good practices to be used with C#. Any suggestions??? (No need of large descriptions :) Just the idea is sufficient.)

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  • C# to VB question

    - by Jim
    Hi, I can achieve in VB what the following C# snippet does but it seems very clunky since I perform a Linq query to obtain the events for the relevant user. Is there a neat way? ctx.FetchEventsForWhichCurrentUserIsRegistered((op) => { if (!op.HasError) { var items = op.Value; _currentUserRegisteredEventIds = new HashSet<int>(items); UpdateRegistrationButtons(); } }, null); } else { _currentUserRegisteredEventIds = null; UpdateRegistrationButtons(); }

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  • JPA entitymanager remove operation is not performant

    - by Samuel
    When I try to do an entityManager.remove(instance) the underlying JPA provider issues a separate delete operation on each of the GroupUser entity. I feel this is not right from a performance perspective, since if a Group has 1000 users there will be 1001 calls issued to delete the entire group and itr groupuser entity. Would it make more sense to write a named query to remove all entries in groupuser table (e.g. delete from group_user where group_id=?), so I would have to make just 2 calls to delete the group. @Entity @Table(name = "tbl_group") public class Group { @OneToMany(mappedBy = "group", cascade = CascadeType.ALL, fetch = FetchType.LAZY) @Cascade(value = DELETE_ORPHAN) private Set<GroupUser> groupUsers = new HashSet<GroupUser>(0);

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  • which collection should I use

    - by Masna
    Hello, I have a number of custom objects of type X. X has a number of parameters and must be unique in the collection. (I created my own equals method based on the custom parameters to examine this) In each object of type x, I have a list of objects y. I want to add/remove/modify easily an object y. For example: To write the add method, it would be something like add(objTypeX, objTypeY) I would check or the collections already has a objTypeX. If so: i would add the objTypeY to the already existing objTypeX else: i would create objTypeX and add objTypeY to this object. To modify an objTypeY, it would be something like(objTypeX, objTypeY, newobjTypeY) I would get objTypeX out of the collections and modify objTypeY to newobjTypeY Which collections should I use? I tried with hashset but i can get a specific object out of the list, without run down the list till I find that object. I develop this in vb.net 3.5

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  • The cost of nested methods

    - by Palimondo
    In Scala one might define methods inside other methods. This limits their scope of use to inside of definition block. I use them to improve readability of code that uses several higher-order functions. In contrast to anonymous function literals, this allows me to give them meaningful names before passing them on. For example: class AggregatedPerson extends HashSet[PersonRecord] { def mostFrequentName: String = { type NameCount = (String, Int) def moreFirst(a: NameCount, b: NameCount) = a._2 > b._2 def countOccurrences(nameGroup: (String, List[PersonRecord])) = (nameGroup._1, nameGroup._2.size) iterator.toList.groupBy(_.fullName). map(countOccurrences).iterator.toList. sortWith(moreFirst).head._1 } } Is there any runtime cost because of the nested method definition I should be aware of? Does the answer differ for closures?

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  • CascadeType problem in One to Many Relation

    - by Milad.KH
    Hi I have two classes which have a Unidirectional One to Many relation with each other. public class Offer{ ... @OneToMany(cascade=CascadeType.ALL) @JoinTable(name = "Offer_Fields", joinColumns = @JoinColumn(name = "OFFER_ID"), inverseJoinColumns = @JoinColumn(name = "FIELDMAPPER_ID")) private Set<FieldMapper> fields = new HashSet<FieldMapper>(); } public class FieldMapper{ ... } I want to store an Offer with a set of FieldMapper to database. When I Use CascadeType.ALL in my OneToMany, I got this error: org.hibernate.HibernateException: Illegal attempt to associate a collection with two open sessions and when I change CascadeType to something else I got this error: org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: com.RCSTT.library.FieldMapper Thanks for your help.

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  • Easiest way of checking if a string consists of unique characters?

    - by serg555
    I need to check in Java if a word consists of unique letters (case insensitive). As straight solution is boring, I came up with: For every char in a string check if indexOf(char) == lastIndexOf(char). Add all chars to HashSet and check if set size == string length. Convert a string to a char array, sort it alphabetically, loop through array elements and check if c[i] == c[i+1]. Currently I like #2 the most, seems like the easiest way. Any other interesting solutions?

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  • Persist collection of interface using Hibernate

    - by Olvagor
    I want to persist my litte zoo with Hibernate: @Entity @Table(name = "zoo") public class Zoo { @OneToMany private Set<Animal> animals = new HashSet<Animal>(); } // Just a marker interface public interface Animal { } @Entity @Table(name = "dog") public class Dog implements Animal { // ID and other properties } @Entity @Table(name = "cat") public class Cat implements Animal { // ID and other properties } When I try to persist the zoo, Hibernate complains: Use of @OneToMany or @ManyToMany targeting an unmapped class: blubb.Zoo.animals[blubb.Animal] I know about the targetEntity-property of @OneToMany but that would mean, only Dogs OR Cats can live in my zoo. Is there any way to persist a collection of an interface, which has several implementations, with Hibernate?

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  • C#: Get a list of every value for a given key in a set of dictionaries?

    - by Rosarch
    How can I write this code more cleanly/concisely? /// <summary> /// Creates a set of valid URIs. /// </summary> /// <param name="levelVariantURIDicts">A collection of dictionaries of the form: /// dict["filePath"] == theFilePath </param> /// <returns></returns> private ICollection<string> URIsOfDicts(ICollection<IDictionary<string, string>> levelVariantURIDicts) { ICollection<string> result = new HashSet<string>(); foreach (IDictionary<string, string> dict in levelVariantURIDicts) { result.Add(dict["filePath"]); } return result; }

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  • Why do I get a nullpointerexception at line ds.getPort in class L1?

    - by Fred
    import java.awt.; import java.awt.event.; import javax.swing.; import java.io.; import java.net.; import java.util.; public class Draw extends JFrame { /* * Socket stuff */ static String host; static int port; static int localport; DatagramSocket ds; Socket socket; Draw d; Paper p = new Paper(ds); public Draw(int localport, String host, int port) { d = this; this.localport = localport; this.host = host; this.port = port; try { ds = new DatagramSocket(localport); InetAddress ia = InetAddress.getByName(host); System.out.println("Attempting to connect DatagramSocket. Local port " + localport + " , foreign host " + host + ", foreign port " + port + "..."); ds.connect(ia, port); System.out.println("Success, ds.localport: " + ds.getLocalPort() + ", ds.port: " + ds.getPort() + ", address: " + ds.getInetAddress()); Reciever r = new Reciever(ds); r.start(); } catch (Exception e) { e.printStackTrace(); } setDefaultCloseOperation(EXIT_ON_CLOSE); getContentPane().add(p, BorderLayout.CENTER); setSize(640, 480); setVisible(true); } public static void main(String[] args) { int x = 0; for (String s : args){ if (x==0){ localport = Integer.parseInt(s); x++; } else if (x==1){ host = s; x++; } else if (x==2){ port = Integer.parseInt(s); } } Draw d = new Draw(localport, host, port); } } class Paper extends JPanel { DatagramSocket ds; private HashSet hs = new HashSet(); public Paper(DatagramSocket ds) { this.ds=ds; setBackground(Color.white); addMouseListener(new L1(ds)); addMouseMotionListener(new L2()); } public void paintComponent(Graphics g) { super.paintComponent(g); g.setColor(Color.black); Iterator i = hs.iterator(); while(i.hasNext()) { Point p = (Point)i.next(); g.fillOval(p.x, p.y, 2, 2); } } private void addPoint(Point p) { hs.add(p); repaint(); } class L1 extends MouseAdapter { DatagramSocket ds; public L1(DatagramSocket ds){ this.ds=ds; } public void mousePressed(MouseEvent me) { addPoint(me.getPoint()); Point p = me.getPoint(); String message = Integer.toString(p.x) + " " + Integer.toString(p.y); System.out.println(message); try{ byte[] data = message.getBytes("UTF-8"); //InetAddress ia = InetAddress.getByName(ds.host); String convertedMessage = new String(data, "UTF-8"); System.out.println("The converted string is " + convertedMessage); DatagramPacket dp = new DatagramPacket(data, data.length); System.out.println(ds.getPort()); //System.out.println(message); //System.out.println(ds.toString()); //ds.send(dp); /*System.out.println("2Sending a packet containing data: " +data +" to " + ia + ":" + d.port + "...");*/ } catch (Exception e){ e.printStackTrace(); } } } class L2 extends MouseMotionAdapter { public void mouseDragged(MouseEvent me) { addPoint(me.getPoint()); Point p = me.getPoint(); String message = Integer.toString(p.x) + " " + Integer.toString(p.y); //System.out.println(message); } } } class Reciever extends Thread{ DatagramSocket ds; byte[] buffer; Reciever(DatagramSocket ds){ this.ds = ds; buffer = new byte[65507]; } public void run(){ try { DatagramPacket packet = new DatagramPacket(buffer, buffer.length); while(true){ try { ds.receive(packet); String s = new String(packet.getData()); System.out.println(s); } catch (Exception e) { e.printStackTrace(); } } } catch (Exception e) { e.printStackTrace(); } } }

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  • Is it possible to give a python dict an initial capacity (and is it usefull)

    - by Peter Smit
    I am filling a python dict with around 10,000,000 items. My understanding of dict (or hashtables) is that when too much elements get in them, the need to resize, an operation that cost quite some time. Is there a way to say to a python dict that you will be storing at least n items in it, so that it can allocate memory from the start? Or will this optimization not do any good to my running speed? (And no, I have not checked that the slowness of my small script is because of this, I actually wouldn't now how to do that. This is however something I would do in Java, set the initial capacity of the HashSet right)

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  • Why is TreeSet<T> an internal type in .NET?

    - by Justin Niessner
    So, I was just digging around Reflector trying to find the implementation details of HashSet (out of sheer curiosity based on the answer to another question here) and noticed the following: internal class TreeSet<T> : ICollection<T>, IEnumerable<T>, ICollection, IEnumerable, ISerializable, IDeserializationCallback Without looking too deep into the details, it looks like a Self-Balancing Binary Search Tree. My question is, is there anybody out there with the insight as to why this class is internal? Is it simply because the other collection types use it internally and hide the complexities of a BST from the general masses...or am I way off base?

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  • How to lowercase every element of a collection efficiently?

    - by Chris
    Whats the most efficient way to lower case every element of a list or set? My idea for a List: final List<String> strings = new ArrayList<String>(); strings.add("HELLO"); strings.add("WORLD"); for(int i=0,l=strings.size();i<l;++i) { strings.add(strings.remove(0).toLowerCase()); } is there a better, faster way? How would this exmaple look like for a set? As there is currently no method for applying an operation to each element of a set (or list) can it be done without creating an additional temporary set? Something like this would be nice: Set<String> strings = new HashSet<String>(); strings.apply( function (element) { this.replace(element, element.toLowerCase();) } ); Thanks,

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  • Is there a good collection library for C-language?

    - by matti
    We have to maintain and even develop C-code of our legacy system. Is there good collection library that would support Java/C# (new versions) style collections. Hashtable, HashSet, etc. Of course without objects, but with structs. The HashTable key limitations to "strings" and ints is not a problem. It wouldn't be bad if it's free even for commercial use. I'm back to C from C# and I must say i'm depressed using our own libraries and the language in general. We're using VS2005 and MS C-compiler if that has nothing to do with anything. Thanks & BR -Matti

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  • How to make code run a certain amount of times before returning something?

    - by user3564967
    I made a trivia game and I have to make a method (SuccessOrFail) that will return whether the user beat the trivia or not. namespace D4 { /// <summary> /// Displays the trivia and returns whether the user succeeded or not, number of questions asked, and a free piece of trivia. /// </summary> public partial class TriviaForm : Form { private Trivia trivia; private Question question; private Random rand = new Random(); private HashSet<int> pickedQuestion = new HashSet<int>(); private string usersAnswer; private int numCorrectAnswers; private int numIncorrectAnswers; public TriviaForm() { InitializeComponent(); this.trivia = new Trivia(); QuestionRandomizer(); QuestionOutputter(); } /// <summary> /// This method will return true if succeeded or false if not. /// </summary> /// <returns>Whether the user got the trivia right or not</returns> public bool SuccessOrFail(bool wumpus) { bool successOrFail = false; int maxQuestions = 3; if (wumpus == true) maxQuestions = 5; int numNeededCorrect = maxQuestions / 2 + 1; if (this.usersAnswer == question.CorrectAnswer.ToString()) numCorrectAnswers++; else numIncorrectAnswers++; if (numCorrectAnswers + numIncorrectAnswers == maxQuestions) { if (numCorrectAnswers == numNeededCorrect) successOrFail = true; else successOrFail = false; numCorrectAnswers = 0; numIncorrectAnswers = 0; return successOrFail; } else return false; } /// <summary> /// This method will output a free answer to the player. /// </summary> public string FreeTrivia() { return question.Freetrivia; } // This method tells the player whether they were correct or not. private void CorrectOrNot() { if (this.usersAnswer == question.CorrectAnswer.ToString()) MessageBox.Show("Correct"); else MessageBox.Show("Incorrect"); } // Displays the questions and answers on the form. private void QuestionOutputter() { this.txtQuestion.Text = question.QuestionText; this.txtBox0.Text = question.Answers[0]; this.txtBox1.Text = question.Answers[1]; this.txtBox2.Text = question.Answers[2]; this.txtBox3.Text = question.Answers[3]; } // Clears the TextBoxes and displays a new random question. private void btnNext_Click(object sender, EventArgs e) { this.usersAnswer = txtAnswer.Text; CorrectOrNot(); this.txtQuestion.Clear(); this.txtBox0.Clear(); this.txtBox1.Clear(); this.txtBox2.Clear(); this.txtBox3.Clear(); this.txtAnswer.Clear(); this.txtAnswer.Focus(); QuestionRandomizer(); QuestionOutputter(); this.txtsuc.Text = SuccessOrFail(false).ToString(); } // Choose a random number and assign the corresponding data to question, refreshes the list if all questions used. private void QuestionRandomizer() { if (pickedQuestion.Count < trivia.AllQuestions.Count) { int random; do { random = rand.Next(trivia.AllQuestions.Count); } while (pickedQuestion.Contains(random)); pickedQuestion.Add(random); this.question = trivia.AllQuestions.ToArray()[random]; if (pickedQuestion.Count == trivia.AllQuestions.ToArray().Length) pickedQuestion.Clear(); } } } } My question is how to make it so that the code asks the user 3 or 5 questions and then returns whether the user won or not? I was wondering if somehow I could make a public void that would just make the form pop up and ask the user 3 to 5 questions and then once it asks the maximum number of questions, to close and then have a method that returns true if the user won, or false if they didn't. But I literally have no idea how to do that. Edit: So I know a for loop can make code run more than once. But the problem I'm having is, is that I don't know how to make it so that the trivia game asks 3 to 5 questions BEFORE returning something.

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  • Hibernate inserting into join table

    - by Karl
    I got several entities. Two of them got a many-to-many relation. When I do a bigger operation on these entities it fails with this exception: org.hibernate.exception.ConstraintViolationException: could not insert collection rows: I execute the operation i a @Transactional context. I don't do any explicit flushing i my daos. The flush is triggered by a query. In the queue are 15 elements (all of the same structure). one of them always fails (but it's always a different one (I checked) and always at a different position). Does anybody have a hint for me for what I might do wrong? My Mapping: @ManyToMany(targetEntity = CategoryImpl.class) protected Set<Category> categories = new HashSet<Category>();

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  • C#: Union of two ICollections? (equivlaent of Java's addAll())

    - by Rosarch
    I have two ICollections of which I would like to take the union. Currently, I'm doing this with a foreach loop, but that feels verbose and hideous. What is the C# equivalent of Java's addAll()? Example of this problem: ICollection<IDictionary<string, string>> result = new HashSet<IDictionary<string, string>>(); // ... ICollection<IDictionary<string, string>> fromSubTree = GetAllTypeWithin(elementName, element); foreach (IDictionary<string, string> dict in fromSubTree) // hacky { result.Add(dict); } // result is now the union of the two sets

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  • Using Custom Generic Collection faster with objects than List

    - by Kaminari
    I'm iterating through a List<> to find a matching element. The problem is that object has only 2 significant values, Name and Link (both strings), but has some other values which I don't want to compare. I'm thinking about using something like HashSet (which is exactly what I'm searching for -- fast) from .NET 3.5 but target framework has to be 2.0. There is something called Power Collections here: http://powercollections.codeplex.com/, should I use that? But maybe there is other way? If not, can you suggest me a suitable custom collection?

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  • Hibernate Save Parent Only

    - by user239905
    Hi, I'm having an issue with Hibernate 3.2.5, where I have to save only the parent object in a one-to-many relationship. For example, I have a flower A, that can have many details. Firstly I want to save only the flower, and the details will be added later. This process throws an exception: not-null property references a null or transient value: com.juflora.bean.JFlora._floraSetBackref This is my code: JFlora flora = new JFlora(); flora.setTypeId(Integer.parseInt(type)); flora.setDescription(description); flora.setName(name); flora.setImage(image); flora.setFloraDetails(new HashSet()); session.save(flora); session.getTransaction().commit();

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  • Whats the best to way convert a set of Java objects to another set of objects?

    - by HDave
    Basic Java question here from a real newbie. I have a set of Java objects (of class "MyClass") that implement a certain interface (Interface "MyIfc"). I have a set of these objects stored in a private variable in my class that is declared as follows: protected Set<MyClass> stuff = new HashSet<MyClass>(); I need to provide a public method that returns this set as a collection of objects of type "MyIfc". public Collection<MyIfc> getMyStuff() {...} How do I do the conversion? The following line gives me an error that it can't do the conversion. I would have guessed the compiler knew that objects of class MyClass implemented MyIfc and therefore would have handled it. Collection<MyIfc> newstuff = stuff; Any enlightenment is appreciated.

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