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  • When to use identity comparison instead of equals?

    - by maaartinus
    I wonder why would anybody want to use identity comparison for fields in equals, like here (Java syntax): class C { private A a; public boolean equals(Object other) { // standard boring prelude if (other==this) return true; if (other==null) return false; if (other.getClass() != this.getClass()) return false; C c = (C) other; // the relevant part if (c.a != this.a) return false; // more tests... and then return true; } // getter, setters, hashCode, ... } Using == is a bit faster than equals and a bit shorter (due to no need for null tests), too, but in what cases (if any) you'd say it's really better to use == for fields inside equals?

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  • Simplifier le code de vos beans Java à l'aide de Commons Lang, Guava et Lombok, par Thierry Leriche-Dessirier

    Bonjour à tous, Je vous propose un article intitulé "Simplifier le code de vos beans Java à l'aide de Commons Lang, Guava et Lombok". Synopsis : Un bean classique, représentant un chien par exemple, peut vite peser des centaines de lignes quand on l'équipe avec les méthodes classiques et indispensables (constructeurs, getters, setters, equals, hashCode, toString, compareTo), même s'il possède peu d'attributs. Dans cet article, nous verrons comment mettre un tel cabot au régime et lui faire une beauté à l'aide de Commons Lang, Guava et Lombok. Nous en profiterons pour comparer ces bibliothèques entre elles et avec le code Java habituel, sans oublier celui qu'Eclipse génère. L'article est disponible ici :

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  • Is it safe StringToHash() to use in Unity?

    - by Sebastian Krysmanski
    I'm currently browsing through the Unity tutorials and saw that they're recommending to use Animator.StringToHash("some string") to created unique ids for animation properties (see here). Since I'm a programmer, to me the word "hash" doesn't represents something unique. Like the Java documentation for hashValue() states: It is not required that if two objects are unequal [...], then calling the hashCode method on each of the two objects must produce distinct integer results. So, according to this (and my definition of "hash"), two strings may have the same hash value. (You can also argue that there are an infinite number of possible strings but only 2^32 possible int values.) So, is there a possibility that StringToHash() will give me an id that actually belongs to another property (than the one I requested the hash for)?

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  • Would md5 hashes allow detection of synced files?

    - by codpursue
    We have to develop our own file management system in Java web application. We need to sync files between our main server and client severs and find out whether all the client server has all the latest version of files. Our files are in pdf, doc and xls format they changes every now and then as and when it is required. What we are thinking of using MD5 checksum to find out hashcode of files on Main server and store it in database. Same would be there in Client Servers database. After comparing records on database we would come to know whether client servers are synced or not. Please suggest if there are any better ways to do the same.

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  • What are the disadvantages to declaring Scala case classes?

    - by Graham Lea
    If you're writing code that's using lots of beautiful, immutable data structures, case classes appear to be a godsend, giving you all of the following for free with just one keyword: Everything immutable by default Getters automatically defined Decent toString() implementation Compliant equals() and hashCode() Companion object with unapply() method for matching But what are the disadvantages of defining an immutable data structure as a case class? What restrictions does it place on the class or its clients? Are there situations where you should prefer a non-case class?

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  • ItemsControl ItemTemplate Binding

    - by Wonko the Sane
    Hi All, In WPF4.0, I have a class that contains other class types as properties (combining multiple data types for display). Something like: public partial class Owner { public string OwnerName { get; set; } public int OwnerId { get; set; } } partial class ForDisplay { public Owner OwnerData { get; set; } public int Credit { get; set; } } In my window, I have an ItemsControl with the following (clipped for clarity): <ItemsControl ItemsSource={Binding}> <ItemsControl.ItemTemplate> <DataTemplate> <local:MyDisplayControl OwnerName={Binding OwnerData.OwnerName} Credit={Binding Credit} /> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl> I then get a collection of display information from the data layer, and set the DataContext of the ItemsControl to this collection. The "Credit" property gets displayed correctly, but the OwnerName property does not. Instead, I get a binding error: Error 40: BindingExpression path error: 'OwnerName' property not found on 'object' ''ForDisplay' (HashCode=449124874)'. BindingExpression:Path=OwnerName; DataItem='ForDisplay' (HashCode=449124874); target element is 'TextBlock' (Name=txtOwnerName'); target property is 'Text' (type 'String') I don't understand why this is attempting to look for the OwnerName property in the ForDisplay class, rather than in the Owner class from the ForDisplay OwnerData property. Edit It appears that it has something to do with using the custom control. If I bind the same properties to a TextBlock, they work correctly. <ItemsControl ItemsSource={Binding}> <ItemsControl.ItemTemplate> <DataTemplate> <StackPanel> <local:MyDisplayControl OwnerName={Binding OwnerData.OwnerName} Credit={Binding Credit} /> <TextBlock Text="{Binding OwnerData.OwnerName}" /> <TextBlock Text="{Binding Credit}" /> </StackPanel> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl> Thanks, wTs

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  • Grails validateable not work for non-persistent domain class

    - by Hoàng Long
    I followed the instruction here: http://www.grails.org/doc/latest/guide/7.%20Validation.html and added into config.groovy: grails.validateable.classes = [liningtest.Warm'] Then added in src/groovy/Warm.groovy (it's a non-persistent domain class): package liningtest import org.codehaus.groovy.grails.validation.Validateable class Warm { String name; int happyCite; Warm(String n, int h) { this.name = n; this.happyCite = h; } static constraints = { name(size: 1..50) happyCite(min: 100) } } But it just doesn't work (both "blank false" & "size: 0..25") for the "hasErrors" function. It always returns false, even when the name is 25. Is this a Grails bug, if yes, is there any work-around? I'm using Grails 1.3.3 UPDATE: I have updated the simplified code. And now I know that constraint "size" can't be used with "blank", but still does not work. My test class in test/unit/liningtest/WarmTests.groovy package liningtest import grails.test.* class WarmTests extends GrailsUnitTestCase { protected void setUp() { super.setUp() } protected void tearDown() { super.tearDown() } void testSomething() { def w = new Warm('Hihi', 3) assert (w.happyCite == 3) assert (w.hasErrors() == true) } } And the error I got: <?xml version="1.0" encoding="UTF-8" ?> <testsuite errors="1" failures="0" hostname="evolus-50b0002c" name="liningtest.WarmTests" tests="1" time="0.062" timestamp="2010-12-16T04:07:47"> <properties /> <testcase classname="liningtest.WarmTests" name="testSomething" time="0.062"> <error message="No signature of method: liningtest.Warm.hasErrors() is applicable for argument types: () values: [] Possible solutions: hashCode()" type="groovy.lang.MissingMethodException">groovy.lang.MissingMethodException: No signature of method: liningtest.Warm.hasErrors() is applicable for argument types: () values: [] Possible solutions: hashCode() at liningtest.WarmTests.testSomething(WarmTests.groovy:18) </error> </testcase> <system-out><![CDATA[--Output from testSomething-- ]]></system-out> <system-err><![CDATA[--Output from testSomething-- ]]></system-err> </testsuite> UPDATE 2: When I don't use Unit test, but try to call hasErrors in the controller, it runs but return false value. (hasErrors return false with Warm('Hihi', 3) ). Does anyone has a clue?

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  • Compute hash of class code at runtime (C#)?

    - by Breck Fresen
    Is it possible to compute the hash of a class at runtime in C# (presumably through reflection)? To be clear, I don't want to compute the hashcode of an instance of said class, I want to compute the hash of the class code itself (if a function in the class changes, I'd expect a different hash code to be computed). Ideally this would only be sensitive to changes in the object code (and not just a hash of the string representation of the code itself). Thanks in advance for your help, -- Breck

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  • EJB failure to update datamodel

    - by Ignacio
    Here my EJB @Entity @Table(name = "modelos") @NamedQueries({ @NamedQuery(name = "Modelos.findAll", query = "SELECT m FROM Modelos m"), @NamedQuery(name = "Modelos.findById", query = "SELECT m FROM Modelos m WHERE m.id = :id"), @NamedQuery(name = "Modelos.findByDescripcion", query = "SELECT m FROM Modelos m WHERE m.descripcion = :descripcion")}) public class Modelos implements Serializable { private static final long serialVersionUID = 1L; @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @Basic(optional = false) @Column(name = "id") private Integer id; @Basic(optional = false) @Column(name = "descripcion") private String descripcion; @OneToMany(cascade = CascadeType.ALL, mappedBy = "idModelo") private Collection produtosCollection; @JoinColumn(name = "id_marca", referencedColumnName = "id") @ManyToOne(optional = false) private Marcas idMarca; public Modelos() { } public Modelos(Integer id) { this.id = id; } public Modelos(Integer id, String descripcion) { this.id = id; this.descripcion = descripcion; } public Modelos(Integer id, Marcas idMarca) { this.id = id; this.idMarca = idMarca; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getDescripcion() { return descripcion; } public void setDescripcion(String descripcion) { this.descripcion = descripcion; } public Collection<Produtos> getProdutosCollection() { return produtosCollection; } public void setProdutosCollection(Collection<Produtos> produtosCollection) { this.produtosCollection = produtosCollection; } public Marcas getIdMarca() { return idMarca; } public void setIdMarca(Marcas idMarca) { this.idMarca = idMarca; } @Override public int hashCode() { int hash = 0; hash += (id != null ? id.hashCode() : 0); return hash; } @Override public boolean equals(Object object) { // TODO: Warning - this method won't work in the case the id fields are not set if (!(object instanceof Modelos)) { return false; } Modelos other = (Modelos) object; if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) { return false; } return true; } @Override public String toString() { return "" + descripcion + ""; } } And the method accesing from the Modelosfacade public List findByMarcas(Marcas idMarca){ return em.createQuery("SELECT id, descripcion FROM Modelos WHERE idMarca = "+idMarca.getId()+"").getResultList(); } And the calling method from the controller public String createByMarcas() { //recreateModel(); items = new ListDataModel(ejbFacade.findByMarcas(current.getIdMarca())); updateCurrentItem(); System.out.println(current.getIdMarca()); return "List"; } I do not understand why I keep falling in an EJB exception.

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  • Optional Argument: compile time constant issue

    - by Jack
    Why is this working: public int DoesEmailAddressExistsExcludingEmailAddressID( string emailAddress, string invitationCode, int emailAddressID = 0, int For = (int) Enums.FOR.AC) whereas this doesn't public int DoesEmailAddressExistsExcludingEmailAddressID( string emailAddress, string invitationCode, int emailAddressID = 0, int For = Enums.FOR.AC.GetHashCode()) where AC is enum. Can enums's hashcode change at runtime?

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  • Ruby: How can I have a Hash take multiple keys?

    - by zxcvbnm
    I'm taking 5 strings (protocol, source IP and port, destination IP and port) and using them to store some values in a hash. The problem is that if the IPs or ports are switched between source and destination, the key is supposed to be the same. If I was doing this in C#/Java/whatever I'd have to create a new class and overwrite the hashcode()/equals() methods, but that seems error prone from the little I've read about it and I was wondering if there would be a better alternative here.

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  • Iteration order of HashSet

    - by eljenso
    If every object added to a java.util.HashSet implements Object.equals() and Object.hashCode() in a deterministic fashion, is the iteration order over the HashSet guaranteed to be identical for every identical set of elements added, irrespective of the order in which they were added?

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  • How to generate a checksum for an java object

    - by Alex
    hi there, I'm looking for an solution to generate a checksum for any type of java object, which remains the same for every exection of an application which produces the same object. I tried it with object.hashcode(), but as I read in the api ....This integer need not remain consistent from one execution of an application to another execution of the same application. thank you, best regard alex

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  • How to Create Own HashMap in Java?

    - by Taranfx
    I know about hashing algorithm and hashCode() to convert "key" into an equivalent integer (using some mathematically random expression) that is then compressed and stored into buckets. But can someone point me to an implementation or at least data structure that should be used as baseline? I haven't found it anywhere on the web.

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  • Any big difference between using contains or loop through a list?

    - by Nazgulled
    Hi, Performance wise, is there really a big difference between using: ArrayList.contains(o) vs foreach|iterator LinkedList.contains(o) vs foreach|iterator HashMap.(containsKey|containsValue) vs foreach|iterator TreeMap.(containsKey|containsValue) vs foreach|iterator Of course, for the foreach|iterator loops, I'll have to explicitly compare the methods and return true or false accordingly. The object I'm comparing is an object where equals() and hashcode() are both properly overridden.

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  • variables reference value of string

    - by xdevel2000
    How can I get the reference value of a string object? If I hava a class like class T() { } T t = new T(); System.out.println( t); print out T@a3455467 that is the reference value inside t but for string? maybe with method hashCode()??

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  • calling dll function from php program

    - by satish-fbg
    I've made a program in php where i got to call a dll function.. that dll contains some hashcode.. i call this dll's function from vb6 through this code: Private Declare Function GetHash Lib "hashGen.dll" (ByVal tEncode As String) As Long Private Sub get_Key() MsgBox GetHash("hello world") end sub can anybody tell me how to call this function in PHP? here's my dll file: http://www.4shared.com/file/-hdichIS/hashGen.html thnx..

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  • Is HashMap in Java collision safe

    - by changed
    Hi I am developing a parser that needs to put key value pairs in hashmap. But a key can have multiple values which i can do in this way HashMap<String,ArrayList<String>> . But what happens if number of keys are very large and it start matching with other key's hashcode. Will that rewrite previous key's value ? thanks -devSunday

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  • Object value not getting updated in the database using hibernate

    - by user1662917
    I am using Spring,hibernate,jsf with jquery in my application. I am inserting a Question object in the database through the hibernate save query . The question object contains id ,question,answertype and reference to a form object using form_id. Now I want to alter the values of Question object stored in the database by altering the value stored in the list of Question objects at the specified index position. If I alter the value in the list the value in the database is not getting altered by update query . Could you please advise. Question.java package com.otv.model; import java.io.Serializable; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.FetchType; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.JoinColumn; import javax.persistence.ManyToOne; import javax.persistence.Table; import org.apache.commons.lang.builder.ToStringBuilder; @Entity @Table(name = "questions") public class Question implements Serializable { @Id @GeneratedValue @Column(name = "id", unique = true, nullable = false) private int id; @Column(name = "question", nullable = false) private String text; @Column(name = "answertype", nullable = false) private String answertype; @ManyToOne(fetch = FetchType.EAGER) @JoinColumn(name = "form_id") private Form form; // @JoinColumn(name = "form_id") // private int formId; public Question() { } public Question(String text, String answertype) { this.text = text; this.answertype = answertype; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getQuestion() { return text; } public void setQuestion(String question) { this.text = question; } public String getAnswertype() { return answertype; } public void setAnswertype(String answertype) { this.answertype = answertype; } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((answertype == null) ? 0 : answertype.hashCode()); result = prime * result + id; result = prime * result + ((text == null) ? 0 : text.hashCode()); return result; } @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; Question other = (Question) obj; if (answertype == null) { if (other.answertype != null) return false; } else if (!answertype.equals(other.answertype)) return false; if (id != other.id) return false; if (text == null) { if (other.text != null) return false; } else if (!text.equals(other.text)) return false; return true; } public void setForm(Form form) { this.form = form; } @Override public String toString() { return ToStringBuilder.reflectionToString(this); } } Form.java package com.otv.model; import java.io.Serializable; import java.util.ArrayList; import java.util.List; import javax.persistence.CascadeType; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.FetchType; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.OneToMany; import javax.persistence.Table; import org.apache.commons.lang.builder.ToStringBuilder; @Entity @Table(name = "FORM") public class Form implements Serializable { @Id @GeneratedValue @Column(name = "id", unique = true, nullable = false) private int id; @Column(name = "name", nullable = false) private String name; @Column(name = "description", nullable = false) private String description; @OneToMany(mappedBy = "form", fetch = FetchType.EAGER, cascade = CascadeType.ALL) List<Question> questions = new ArrayList<Question>(); public Form(String name) { super(); this.name = name; } public Form() { super(); } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getDescription() { return description; } public void setDescription(String description) { this.description = description; } public List<Question> getQuestions() { return questions; } public void setQuestions(List<Question> formQuestions) { this.questions = formQuestions; } public void addQuestion(Question question) { questions.add(question); question.setForm(this); } public void removeQuestion(Question question) { questions.remove(question); question.setForm(this); } @Override public String toString() { return ToStringBuilder.reflectionToString(this); } public void replaceQuestion(int index, Question question) { Question prevQuestion = questions.get(index); // prevQuestion.setQuestion(question.getQuestion()); // prevQuestion.setAnswertype(question.getAnswertype()); question.setId(prevQuestion.getId()); question.setForm(this); questions.set(index, question); } } QuestionDAO.java package com.otv.user.dao; import java.util.List; import org.hibernate.SessionFactory; import com.otv.model.Question; public class QuestionDAO implements IQuestionDAO { private SessionFactory sessionFactory; public SessionFactory getSessionFactory() { return sessionFactory; } public void setSessionFactory(SessionFactory sessionFactory) { this.sessionFactory = sessionFactory; } public void addQuestion(Question question) { getSessionFactory().getCurrentSession().save(question); } public void deleteQuestion(Question question) { getSessionFactory().getCurrentSession().delete(question); } public void updateQuestion(Question question) { getSessionFactory().getCurrentSession().update(question); } public Question getQuestionById(int id) { List list = getSessionFactory().getCurrentSession().createQuery("from Questions where id=?") .setParameter(0, id).list(); return (Question) list.get(0); } }

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  • Is the Google Annotations Gallery useful in production code?

    - by cafe
    I could actually see a use for the Google Annotations Gallery in real code: Stumble across code that somehow works beyond all reason? Life's short. Mark it with @Magic and move on: @Magic public static int negate(int n) { return new Byte((byte) 0xFF).hashCode() / (int) (short) '\uFFFF' * ~0 * Character.digit ('0', 0) * n * (Integer.MAX_VALUE * 2 + 1) / (Byte.MIN_VALUE >> 7) * (~1 | 1); } This is a serious question. Could this be used in an actual code review?

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  • Java lang object

    - by Neeraj
    why java Object class has two methods hashcode() and equals()? One of them looks redundant and its percolated to the bottom most derived class?

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  • Java: If I overwrite the .equals method, can I still test for reference equality with ==?

    - by shots fired
    I have the following situation: I need to sort trees based by height, so I made the Tree's comparable using the height attribute. However, I was also told to overwrite the equals and hashCode methods to avoid unpredictable behaviour. Still, sometimes I may want to compare the references of the roots or something along those lines using ==. Is that still possible or does the == comparison call the equals method?

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