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  • How do I make my ArrayList Thread-Safe? Another approach to problem in Java?

    - by thechiman
    I have an ArrayList that I want to use to hold RaceCar objects that extend the Thread class as soon as they are finished executing. A class, called Race, handles this ArrayList using a callback method that the RaceCar object calls when it is finished executing. The callback method, addFinisher(RaceCar finisher), adds the RaceCar object to the ArrayList. This is supposed to give the order in which the Threads finish executing. I know that ArrayList isn't synchronized and thus isn't thread-safe. I tried using the Collections.synchronizedCollection(c Collection) method by passing in a new ArrayList and assigning the returned Collection to an ArrayList. However, this gives me a compiler error: Race.java:41: incompatible types found : java.util.Collection required: java.util.ArrayList finishingOrder = Collections.synchronizedCollection(new ArrayList(numberOfRaceCars)); Here is the relevant code: public class Race implements RaceListener { private Thread[] racers; private ArrayList finishingOrder; //Make an ArrayList to hold RaceCar objects to determine winners finishingOrder = Collections.synchronizedCollection(new ArrayList(numberOfRaceCars)); //Fill array with RaceCar objects for(int i=0; i<numberOfRaceCars; i++) { racers[i] = new RaceCar(laps, inputs[i]); //Add this as a RaceListener to each RaceCar ((RaceCar) racers[i]).addRaceListener(this); } //Implement the one method in the RaceListener interface public void addFinisher(RaceCar finisher) { finishingOrder.add(finisher); } What I need to know is, am I using a correct approach and if not, what should I use to make my code thread-safe? Thanks for the help!

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  • Is it safe to silently catch ClassCastException when searching for a specific value?

    - by finnw
    Suppose I am implementing a sorted collection (simple example - a Set based on a sorted array.) Consider this (incomplete) implementation: import java.util.*; public class SortedArraySet<E> extends AbstractSet<E> { @SuppressWarnings("unchecked") public SortedArraySet(Collection<E> source, Comparator<E> comparator) { this.comparator = (Comparator<Object>) comparator; this.array = source.toArray(); Collections.sort(Arrays.asList(array), this.comparator); } @Override public boolean contains(Object key) { return Collections.binarySearch(Arrays.asList(array), key, comparator) >= 0; } private final Object[] array; private final Comparator<Object> comparator; } Now let's create a set of integers Set<Integer> s = new SortedArraySet<Integer>(Arrays.asList(1, 2, 3), null); And test whether it contains some specific values: System.out.println(s.contains(2)); System.out.println(s.contains(42)); System.out.println(s.contains("42")); The third line above will throw a ClassCastException. Not what I want. I would prefer it to return false (as HashSet does.) I can get this behaviour by catching the exception and returning false: @Override public boolean contains(Object key) { try { return Collections.binarySearch(Arrays.asList(array), key, comparator) >= 0; } catch (ClassCastException e) { return false; } } Assuming the source collection is correctly typed, what could go wrong if I do this?

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  • Compiling Java code in terminal having a Jar in CLASSPATH

    - by Masi
    How can you compile the code using javac in a terminal by using google-collections in CLASSPATH? Example of code trying to compile using javac in a terminal (works in Eclipse) import com.google.common.collect.BiMap; import com.google.common.collect.HashBiMap; public class Locate { ... BiMap<MyFile, Integer> rankingToResult = HashBiMap.create(); ... } Compiling in terminal src 288 % javac Locate.java Locate.java:14: package com.google.common.collect does not exist import com.google.common.collect.BiMap; ^ Locate.java:15: package com.google.common.collect does not exist import com.google.common.collect.HashBiMap; ^ Locate.java:153: cannot find symbol symbol : class BiMap location: class Locate BiMap<MyFile, Integer> rankingToResult = HashBiMap.create(); ^ Locate.java:153: cannot find symbol symbol : variable HashBiMap location: class Locate BiMap<MyFile, Integer> rankingToResult = HashBiMap.create(); ^ 4 errors My CLASSPATH src 289 % echo $CLASSPATH /u/1/bin/javaLibraries/google-collect-1.0.jar

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  • WPF: IEditableCollectionView and CanAddNew and empty collections

    - by Aran Mulholland
    We were having some issues with the wpf datagrid and IEditableCollectionView (although this question applies to using IEditableCollectionView and ItemsControl) When you have a collection with no items in it, the IEditableCollectionView cannot determine what items should be inserted so it sets CanAddNew=false we found a solution here (buried deep in the comments) that goes like so : If you derive from ObservableCollection like this public class PersonsList : ObservableCollection<Person> { } you will find out that if the initial collection is empty, there won't be a NewItemPlaceHolder showing up on the view. That's because PersonsList cannot resolve type T at design time. A workaround that works for me is to pass type T as a parameter into the class like this PersonsList<T> : ObservableCollection<T> where T : Person { } This approach will place the NewItemPlaceHolder even if the collection is empty. I'm wondering if there is an interface i can implement on my collections that inform the IEditableCollectionView which type to create should i get an AddNew request.

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  • silverlight with WCF(get data through collections)

    - by Piyush
    in my silverlight page I am fetching the data through WCF WCF is returning an BusinessEntityCollection that is the collection of rows SqlParameter[] sqlParameter = new SqlParameter[]{new SqlParameter("@recordType",recordType)}; MenuEntity menuEntity; MenuEntityCollection menuEntityCollection = new MenuEntityCollection(); using (SqlDataReader sqlDataReader = SqlHelper.ExecuteReader(_ConnectionString,CommandType.StoredProcedure, StoredProcedures.GetMenus, sqlParameter)) { if (sqlDataReader.Read()) { menuEntity = new MenuEntity(); DataAccessHelper.GetEntity(sqlDataReader, menuEntity); menuEntityCollection.Add(menuEntity); } } return menuEntityCollection; -- in silverlight page when I am calling WCF there I am getting an error MenuEntity menuList = new MenuEntity(); menuList = e.Result; <-----error line error: Cannot implicitly convert type 'System.Collections.ObjectModel.ObservableCollection' to 'FastTrackSLUI.AdminServiceReference.MenuEntity'

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  • How to include simple collections in ConfigurationSection

    - by mikemanne
    Is there a way for me to include a simple array of strings, or List<string> on my custom subclass of ConfigurationSection? (Or an array or generic list of simple data objects, for that matter?) I'm becoming familiar with the new (and VERY verbose) ConfigurationSection, ConfigurationElement, and ConfigurationElementCollection classes, but I'm by no means an expert yet. It seems like ConfigurationSection should handle simple collections/lists on its own, without me having to create a custom ConfigurationElementCollection subclass for each and every one. But I haven't found any reference to this ability online.

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  • Visual Studio XSD Tool: Generate Collections Rather Than Arrays

    - by senfo
    I generated some C# classes from an XSD using the Visual Studio XSD utility and it generated arrays for storing a collection of elements, rather than one of the built-in generic Collection<T> (or related) classes. None of the command line parameters mentioned in xsd /? mention anything about generating collections rather than arrays, but I know that this can be done with web service proxy classes that Visual Studio generates, so I figured it must be possible. Does anybody know how to have the XSD utility generate collection classes rather than arrays?

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  • Signature of Collections.min/max method

    - by Marco
    In Java, the Collections class contains the following method: public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> c) Its signature is well-known for its advanced use of generics, so much that it is mentioned in the Java in a Nutshell book and in the official Sun Generics Tutorial. However, I could not find a convincing answer to the following question: Why is the formal parameter of type Collection<? extends T>, rather than Collection<T>? What's the added benefit?

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  • Two collections manyToOne to same primary key

    - by Ethiel
    Hi, guys, I'm coding a web page in Hibernate-JPA and Oracle. I need the following: I have two classes: Place and Home. I need two collections of type Place in every Home: I do the following: Home: @ManyToOne @JoinColumn(name="ID_PLACES") private List<Places>places1; @ManyToOne @JoinColumn(name="ID_PLACES") private List<Places>Places2; However, hibernate got an exception (repeated column) and forces to me to mapping with insert and update to false. How Can I get Two ManyToOne relationship to same primary key with insert a true?.

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  • DTOs Collections mapping Problem

    - by the_knight5000
    I'm working now on a multi-tier project which has layers as following : DAL BLL GUI Layer and Shared DTOs between BLL and GUI layers. I'm facing a problem in mapping the Objects from DAO To DTO, No problem in the simple objects. The problem is in the Objects who have child collections of another objects. ex: Author Category --Categories --Authors the execution goes in an infinite loop of mapping and it get more complex when I want model Self-join tables ex: Safe Safe --TransferSafe(Collection<Safe>) --TransferSafe(Collection<Safe>) the execution goes in an infinite loop of mapping any suggestions about a good solution or a practical mapping pattern?

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  • odd behavior with java collections of parameterized Class objects

    - by Paul
    Ran into some questionable behavior using lists of parameterized Class objects: ArrayList<Class<String>> classList = new ArrayList<Class<String>>(); classList.add(Integer.class); //compile error Class intClass = Integer.class; classList.add(intClass); //legal apparently, as long as intClass is not parameterized Found the same behavior for LinkedList, haven't tried other collections. Is it like this for a reason? Or have I stumbled on something?

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  • iTextSharp error - cannot convert type 'Collections.Generic.List' to 'iTextSharp.text.Element'

    - by mike
    I am trying to export pdf file using aspx and c#. I got the following error. Cannot implicitly convert type 'System.Collections.Generic.List'' to 'iTextSharp.text.Element' I have the following code using iTextSharp.text; using iTextSharp.text.pdf; using iTextSharp.text.html.simpleparser; StringBuilder strB = new StringBuilder(); document.Open(); if (text.Length.Equals(0))//export the text { GridView1.DataBind(); using (StringWriter sWriter = new StringWriter(strB)) { using (HtmlTextWriter htWriter = new HtmlTextWriter(sWriter)) { GridView1.RenderControl(htWriter); } } } else //export the grid { strB.Append(text); } using (TextReader sReader = new StringReader(strB.ToString())) { StyleSheet styles = new StyleSheet(); List<Element> list = new List<Element>(); list = HTMLWorker.ParseToList(sReader, styles); foreach (IElement elm in list) { document.Add(elm); } } I got the error in this line: list = HTMLWorker.ParseToList(sReader, styles); It's the first time that I am trying to export pdf files. I tried to cast the list element , however this did not solve my error. Any advice would be helpful!!!

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  • Validation Summary for Collections

    - by Myster
    Hi All, EDIT: upgraded this question to MVC 2.0 With asp.net MVC 2.0 is there an existing method of creating Validation Summary that makes sense for models containing collections? If not I can create my own validation summary Example Model: public class GroupDetailsViewModel { public string GroupName { get; set; } public int NumberOfPeople { get; set; } public List<Person> People{ get; set; } } public class Person { [Required(ErrorMessage = "Please enter your Email Address")] [RegularExpression(@"^([a-zA-Z0-9_\-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([a-zA-Z0-9\-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$", ErrorMessage = "Please enter a valid Email Address")] public string EmailAddress { get; set; } [Required(ErrorMessage = "Please enter your Phone Number")] public string Phone { get; set; } [Required(ErrorMessage = "Please enter your First Name")] public string FirstName { get; set; } [Required(ErrorMessage = "Please enter your Last Name")] public string LastName { get; set; } } The existing summary <%=Html.ValidationSummary %> if nothing is entered looks like this. The following error(s) must be corrected before proceeding to the next step * Please enter your Email Address * Please enter your Phone Number * Please enter your First Name * Please enter your Last Name * Please enter your Email Address * Please enter your Phone Number * Please enter your First Name * Please enter your Last Name The design calls for headings to be inserted like this: The following error(s) must be corrected before proceeding to the next step Person 1 * Please enter your Email Address * Please enter your Phone Number * Please enter your First Name * Please enter your Last Name Person 2 * Please enter your Email Address * Please enter your Phone Number * Please enter your First Name * Please enter your Last Name

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  • Essence of BiMap in Google collections

    - by littleEinstein
    I am still quite puzzled at the BiMap in Google collections/Guava. It was claimed that The two bimaps are backed by the same data; any changes to one will appear in the other. I browsed through the source code, and I found the use of delegate in ForwardingMap. But in any actually subclass of StandardBiMap, I do see the data are put into both the forward and reverse map. So what is the essence, and why it claims to have saved space by keeping only one copy of the data? Is it just the actual objects are one set, but two distinct sets of references to these objects are still needed, one set maintained in forward map, and the other in reverse map? private V putInBothMaps(K key, V value, boolean force) { boolean containedKey = containsKey(key); if (containedKey && Objects.equal(value, get(key))) { return value; } if (force) { inverse().remove(value); } else if (containsValue(value)) { throw new IllegalArgumentException( "value already present: " + value); } V oldValue = super.put(key, value); updateInverseMap(key, containedKey, oldValue, value); return oldValue; }

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  • Date Filtered Collections without Functions

    - by madcapnmckay
    Hi, I have an entity similar to the below: public class Entity { public List<DateItem> PastDates { get; set; } public List<DateItem> FutureDates { get; set; } } public class DateItem { public DateTime Date { get; set; } /* * Other Properties * */ } Where PastDates and FutureDates are both mapped to the same type/table. I have been trying to find a way to have the Past and Future properties mapped automagically by Nhibernate. The closest I came was where clause on the mapping as follows HasMany(x => x.PastDates) .AsBag().Cascade .AllDeleteOrphan() .KeyColumnNames.Add("EventId").Where("Date < currentdate()") .Inverse(); Where currentdate is a UDF. I do not want to have these database specific functions if I can avoid it, mostly because i can't then test my DAL with SQLite as it doesn't support functions or stored procedures. At the moment I am building the past and future collections using Criteria and adding to my DTO manually. Anyone know how this could be achieved without using any UDFs? Many thanks,

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  • ArrayList<Int> Collections.Sort and LineNumberReader Help How to

    - by user1819551
    I have a issue i can't get it to work now let going to the point a explain in the code thanks. This is my class: what I want to do is insert the Integers sort the list and buffer writer in a column with out coma. Now I getting this: [1110018, 1110032, 1110056, 1110059, 1110063, 1110085, 1110096, 1110123, 1110125, 1110185, 1110456, 1110459] I want like this: 111xxxxx 111xxxx xxxx....... I can't do it in single array, have to be in ArrayList. This is my collecting: list.addNumbers(numbers); list.display(); This is my writer: Is buffered coma.write("\n"+list.display()); coma.flush();<br/> Here is my class: public class IdCount {<br/> private ArrayList<Integer> properNumber = new ArrayList<>(); public void addNumbers(Integer numbers) { properNumber.add(numbers); Collections.sort(properNumber); } public String display() { //(I try .toString() Not work) return properNumber.toString(); } My second issue is LineNumberReader: This is my collecting and my writing: try { Reader input = new BufferedReader( new FileReader(inputFile)); try (Scanner in = new Scanner(input)) { while (in.hasNext()) { //(More Code) asp = new LineNumberReader(input); int rom = 0; while (asp.readLine()!=null){ rom++; } System.out.println(rom); coma.write(rom); This one will not write anything an my System Print give me only 12 0 in column.

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  • Automapping Collections

    - by vaibhav
    I am using Automapper for mapping my domain model and DTO. When I map Mapper.Map<SiteDTO, SiteEntity> it works fine. But when I use collections of the same entities, it doesn't map. Mapper.Map<Collection<SiteEntity>, Collection<SiteDTO>>(siteEntityCollection); AS per Automapper Wiki, it says the lists implementing ICollection would be mapped, I am using Collection that implements ICollection, but automapper doesn't map it. Am I doing something wrong. public class SiteEntity //SiteDTO has exactly the same properties, so I am not posting it here. { public int SiteID { get; set; } public string Code { get; set; } public string Name { get; set; } public byte Status { get; set; } public int ModifiedBy { get; set; } public DateTime ModifiedDate{ get; set; } public long TimeStamp{ get; set; } public string Description{ get; set; } public string Notes{ get; set; } public ObservableCollection<AreaEntity> Areas{ get; set; } }

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  • Synchronize write to two collections

    - by glaz666
    I need to put some value to maps if it is not there yet. The key-value (if set) should always be in two collections (that is put should happen in two maps atomically). I have tried to implement this as follows: private final ConcurrentMap<String, Object> map1 = new ConcurrentHashMap<String, Object>(); private final ConcurrentMap<String, Object> map2 = new ConcurrentHashMap<String, Object>(); public Object putIfAbsent(String key) { Object retval = map1.get(key); if (retval == null) { synchronized (map1) { retval = map1.get(key); if (retval == null) { Object value = new Object(); //or get it somewhere synchronized (map2) { map1.put(key, value); map2.put(key, new Object()); } retval = value; } } } return retval; } public void doSomething(String key) { Object obj1 = map1.get(key); Object obj2 = map2.get(key); //do smth } Will that work fine in all cases? Thanks

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  • Functional way to get a matrix from text

    - by Elazar Leibovich
    I'm trying to solve some Google Code Jam problems, where an input matrix is typically given in this form: 2 3 #matrix dimensions 1 2 3 4 5 6 7 8 9 # all 3 elements in the first row 2 3 4 5 6 7 8 9 0 # each element is composed of three integers where each element of the matrix is composed of, say, three integers. So this example should be converted to #!scala Array( Array(A(1,2,3),A(4,5,6),A(7,8,9), Array(A(2,3,4),A(5,6,7),A(8,9,0), ) An imperative solution would be of the form #!python input = """2 3 1 2 3 4 5 6 7 8 9 2 3 4 5 6 7 8 9 0 """ lines = input.split('\n') print lines[0] m,n = (int(x) for x in lines[0].split()) array = [] row = [] A = [] for line in lines[1:]: for elt in line.split(): A.append(elt) if len(A)== 3: row.append(A) A = [] array.append(row) row = [] from pprint import pprint pprint(array) A functional solution I've thought of is #!scala def splitList[A](l:List[A],i:Int):List[List[A]] = { if (l.isEmpty) return List[List[A]]() val (head,tail) = l.splitAt(i) return head :: splitList(tail,i) } def readMatrix(src:Iterator[String]):Array[Array[TrafficLight]] = { val Array(x,y) = src.next.split(" +").map(_.trim.toInt) val mat = src.take(x).toList.map(_.split(" "). map(_.trim.toInt)). map(a => splitList(a.toList,3). map(b => TrafficLight(b(0),b(1),b(2)) ).toArray ).toArray return mat } But I really feel it's the wrong way to go because: I'm using the functional List structure for each line, and then convert it to an array. The whole code seems much less efficeint I find it longer less elegant and much less readable than the python solution. It is harder to which of the map functions operates on what, as they all use the same semantics. What is the right functional way to do that?

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  • What's the largest (most complex) PHP algorithm ever implemented in a single monolithic PHP script?

    - by Alex R
    I'm working on a tool which converts PHP code to Scala. As one of the finishing touches, I'm in need of a really good (er, somewhat biased) benchmark. By dumb luck my first benchmark attempt was with some code which uses bcmath extensively, which unfortunately is 1000x slower in Java, making the Scala code 22x slower overall than the original PHP. So I'm looking for some meaningful PHP benchmark with the following characteristics: The source needs to be in a single file. I need it to be simple to setup - no databases, hard-to-find input files, etc. Simple text input and output preferred. It should not use features that are slow in Java (BigInteger, trigonometric functions, etc). It should not use exoteric or dynamic PHP functions (e.g. no "eval" or "variable vars"). It should not over-rely on built-in libraries, e.g. MD5, crypt, etc. It should not be I/O bound. A CPU-bound memory-hungry algorithm is preferred. Basically, intensive OO operations, integer and string manipulation, recursion, etc would be great. Thanks

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  • Is there a PHP benchmark that meets these specific criteria? [closed]

    - by Alex R
    I'm working on a tool which converts PHP code to Scala. As one of the finishing touches, I'm in need of a really good (er, somewhat biased) benchmark. By dumb luck my first benchmark attempt was with some code which uses bcmath extensively, which unfortunately is 1000x slower in Java, making the Scala code 22x slower overall than the original PHP. So I'm looking for some meaningful PHP benchmark with the following characteristics: The PHP source needs to be in a single file. It should solve a real-world problem. No silly looping over empty methods etc. I need it to be simple to setup - no databases, hard-to-find input files, etc. Simple text input and output preferred. It should not use features that are slow in Java (BigInteger, trigonometric functions, etc). It should not use exoteric or dynamic PHP functions (e.g. no "eval" or "variable vars"). It should not over-rely on built-in libraries, e.g. MD5, crypt, etc. It should not be I/O bound. A CPU-bound memory-hungry algorithm is preferred. Basically, intensive OO operations, integer and string manipulation, recursion, etc would be great. Thanks

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  • Is there a general concrete implementation of a KeyedCollection?

    - by CodeSavvyGeek
    The System.Collections.ObjectModel.KeyedCollection class is a very useful alternative to System.Collections.Generic.Dictionary, especially when the key data is part of the object being stored or you want to be able to enumerate the items in order. Unfortunately, the class is abstract, and I am unable to find a general concrete implementation in the core .NET framework. The Framework Design Guidlines book indicates that a concrete implementation should be provided for abstract types (section 4.4 Abstract Class Design). Why would the framework designers leave out a general concrete implementation of such a useful class, especially when it could be provided by simply exposing a constructor that accepts and stores a Converter from the item to its key: public class ConcreteKeyedCollection : KeyedCollection { private Converter getKeyForItem = null; public GenericKeyedCollection(Converter getKeyForItem) { if (getKeyForItem == null) { throw new ArgumentNullException("getKeyForItem"); } this.getKeyForItem = getKeyForItem; } protected override TKey GetKeyForItem(TItem item) { return this.getKeyForItem(item); } }

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  • Quaere - Anyone using it yet? (LINQ to Objects for Java)

    - by Marty Pitt
    Hi there I'm a .NET guy originally, working in Java recently, and finding I'm really missing LINQ to Objects, specifically for performing filtering against collections. A few people here on Stack Overflow have answered the "LINQ for Java?" question with a single word : Quaere However, on the site it clearly states "Pre-Beta", and there's been no commits to their code for over a year, so I'm guessing the project is pretty much dead. Is anyone actually using this, and / or have any experience with it? The second most common answer appears to be "use Google Collections". Is this the most appropriate Java way? Cheers Marty

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