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  • Does this code describe an Existential Type in C#?

    - by noblethrasher
    Currently watching Bart De Smet's explanation of IQueryable and he mentioned Existential Types (which I've been curious about for some time). After reading the answers to this question I'm just wondering if this is a way to construct it in C#: public abstract class ExistentialType { private ExistentialType() { } public abstract int Foo(); public ExistentialType Create() { return new ConcreateType1(); } private class ConcreateType1 : ExistentialType { public override int Foo() { throw new NotImplementedException(); } } private class ConcreateType2 : ExistentialType { public override int Foo() { throw new NotImplementedException(); } } private class ConcreateType3 : ExistentialType { public override int Foo() { throw new NotImplementedException(); } } }

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  • Is it possible to use pure Encrypting and Decrypting keys in asymmetric cryptography instead of priv

    - by macropas
    Is it possible to use pure Encrypting and Decrypting keys instead of private and public keys? As I know in .Net asymmetric RSA implementation private key RSAParameters parameters = (new RSACryptoServiceProvider()).ExportParameters(true) is a superset of public key. And using private key we can both encrypt and decrypt our data. But I need key only for decrypting data. How to do it? I experimented on nulling RSAParameters fields, but RSACryptoServiceProvider object can't import such parameters.

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  • What Good way to keep some different data in Cookies in asp.net?

    - by Dmitriy
    Hello! I want to keep some different data in one cookie file and write this class, and want to know - is this good? For example - user JS enable.When user open his first page on my site, i write to session his GMT time and write with this manager JS state. (GMT time is ajax request with js). And i want to keep some data in this cookie (up to 10 values). Have any advices or tips? /// <summary> /// CookiesSettings /// </summary> internal enum CookieSetting { IsJsEnable = 1, } internal class CookieSettingValue { public CookieSetting Type { get; set; } public string Value { get; set; } } /// <summary> /// Cookies to long time of expire /// </summary> internal class CookieManager { //User Public Settings private const string CookieValueName = "UPSettings"; private string[] DelimeterValue = new string[1] { "#" }; //cookie daat private List<CookieSettingValue> _data; public CookieManager() { _data = LoadFromCookies(); } #region Save and load /// <summary> /// Load from cookie string value /// </summary> private List<CookieSettingValue> LoadFromCookies() { if (!CookieHelper.RequestCookies.Contains(CookieValueName)) return new List<CookieSettingValue>(); _data = new List<CookieSettingValue>(); string data = CookieHelper.RequestCookies[CookieValueName].ToString(); string[] dels = data.Split(DelimeterValue, StringSplitOptions.RemoveEmptyEntries); foreach (string delValue in dels) { int eqIndex = delValue.IndexOf("="); if (eqIndex == -1) continue; int cookieType = ValidationHelper.GetInteger(delValue.Substring(0, eqIndex), 0); if (!Enum.IsDefined(typeof(CookieSetting), cookieType)) continue; CookieSettingValue value = new CookieSettingValue(); value.Type = (CookieSetting)cookieType; value.Value = delValue.Substring(eqIndex + 1, delValue.Length - eqIndex-1); _data.Add(value); } return _data; } public void Save() { CookieHelper.SetValue(CookieValueName, ToCookie(), DateTime.UtcNow.AddMonths(6)); } #endregion #region Get value public bool Bool(CookieSetting type, bool defaultValue) { CookieSettingValue inList = _data.SingleOrDefault(x => x.Type == type); if (inList == null) return defaultValue; return ValidationHelper.GetBoolean(inList.Value, defaultValue); } #endregion #region Set value public void SetValue(CookieSetting type, int value) { CookieSettingValue inList = _data.SingleOrDefault(x => x.Type == type); if (inList == null) { inList = new CookieSettingValue(); inList.Type = type; inList.Value = value.ToString(); _data.Add(inList); } else { inList.Value = value.ToString(); } } public void SetValue(CookieSetting type, bool value) { CookieSettingValue inList = _data.SingleOrDefault(x => x.Type == type); if (inList == null) { inList = new CookieSettingValue(); inList.Type = type; inList.Value = value.ToString(); _data.Add(inList); } else { inList.Value = value.ToString(); } } #endregion #region Private methods private string ToCookie() { StringBuilder sb = new StringBuilder(); for (int i = 0; i < _data.Count; i++) { sb.Append((int)_data[i].Type); sb.Append("="); sb.Append(_data[i].Value); sb.Append(DelimeterValue[0]); } return sb.ToString(); } /// <summary> /// Cookie length in bytes. Max - 4 bytes /// </summary> /// <returns></returns> private int GetLength() { return System.Text.Encoding.UTF8.GetByteCount(ToCookie()); } #endregion } P.S. i want to keep many data in one cookies file to compress data and decrease cookies count.

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  • Call HashMap from jsp EL ?

    - by Parhs
    Here is my Entity Class public enum UnitType { HOSPITAL, HEALTHCENTER } public static LinkedHashMap<UnitType, String> unitType = new LinkedHashMap<UnitType, String>() { { put(UnitType.HEALTHCENTER, "???t?? ??e?a?"); put(UnitType.HOSPITAL, "??s???µe??"); } }; @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; private String name; private String address; @Column(columnDefinition = "TEXT") private String info; @Enumerated(EnumType.STRING) private UnitType type; At my jsp <c:forEach var="unit" items="${requestScope.units}"> <tr> <td>${unit.id}</td> <td>${unit.name}</td> <td>${unit.address}</td> <td>??!?</td> <td><a href="#">?e??ss?te?a</a></td> </tr> </c:forEach> How can i place the text value of the enum at ??!? .. Any idea? Tried some ways but nothing worked..

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  • Loading child entities with JPA on Google App Engine

    - by Phil H
    I am not able to get child entities to load once they are persisted on Google App Engine. I am certain that they are saving because I can see them in the datastore. For example if I have the following two entities. public class Parent implements Serializable{ @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @Extension(vendorName="datanucleus", key="gae.encoded-pk", value="true") private String key; @OneToMany(cascade=CascadeType.ALL) private List<Child> children = new ArrayList<Child>(); //getters and setters } public class Child implements Serializable{ @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @Extension(vendorName="datanucleus", key="gae.encoded-pk", value="true") private String key; private String name; @ManyToOne private Parent parent; //getters and setters } I can save the parent and a child just fine using the following: Parent parent = new Parent(); Child child = new Child(); child.setName("Child Object"); parent.getChildren().add(child); em.persist(parent); However when I try to load the parent and then try to access the children (I know GAE lazy loads) I do not get the child records. //parent already successfully loaded parent.getChildren.size(); // this returns 0 I've looked at tutorial after tutorial and nothing has worked so far. I'm using version 1.3.3.1 of the SDK. I've seen the problem mentioned on various blogs and even the App Engine forums but the answer is always JDO related. Am I doing something wrong or has anyone else had this problem and solved it for JPA?

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  • How to create an entity with a composite primary key containing a generated value.

    - by David
    Using Hibernate + annotations, I'm trying to do the following: Two entities, Entity1 and Entity2. Entity1 contains a simple generated value primary key. Entity2 primary key is composed by a simple generated value + the id of entity one (with a many to one relationship) Unfortunately, I can't make it work. Here is an excerpt of the code: @Entity public class Entity1 { @Id @GeneratedValue private Long id; private String name; ... } @Entity public class Entity2 { @EmbeddedId private Entity2PK pk = new Entity2PK(); private String miscData; ... } @Embeddable public class Entity2PK implements Serializable { @GeneratedValue private Long id; @ManyToOne private Entity1 entity; } void test() { Entity1 e1 = new Entity1(); e1.setName("nameE1"); Entity2 e2 = new Entity2(); e2.setEntity1(e1); e2.setMiscData("test"); Transaction transaction = session.getTransaction(); try { transaction.begin(); session.save(e1); session.save(e2); transaction.commit(); } catch (Exception e) { transaction.rollback(); } finally { session.close(); } } When I run the test method I get the following errors: Hibernate: insert into Entity1 (id, name) values (null, ?) Hibernate: call identity() Hibernate: insert into Entity2 (miscData, entity_id, id) values (?, ?, ?) 07-Jun-2010 10:51:11 org.hibernate.util.JDBCExceptionReporter logExceptions WARNING: SQL Error: 0, SQLState: null 07-Jun-2010 10:51:11 org.hibernate.util.JDBCExceptionReporter logExceptions SEVERE: failed batch 07-Jun-2010 10:51:11 org.hibernate.event.def.AbstractFlushingEventListener performExecutions SEVERE: Could not synchronize database state with session org.hibernate.exception.GenericJDBCException: Could not execute JDBC batch update at org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:103) at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:91) at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43) at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:254) at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:266) at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:167) at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:298) at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:27) at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1001) at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:339) at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:106) at test.App.main(App.java:32) Caused by: java.sql.BatchUpdateException: failed batch at org.hsqldb.jdbc.jdbcStatement.executeBatch(Unknown Source) at org.hsqldb.jdbc.jdbcPreparedStatement.executeBatch(Unknown Source) at org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:48) at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:247) ... 8 more Note that I use HSQLDB. Any ideas about what is wrong ?

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  • how to create class alert using lcdui package in blackberry

    - by Baby
    Advance Thanks.i am new to blackberry developement.i try the following code for creating alert using lcdui package.but nothing will coming when i am running Plz help me. package alertpack; import javax.microedition.lcdui.Alert; import javax.microedition.lcdui.AlertType; import javax.microedition.lcdui.Command; import javax.microedition.lcdui.CommandListener; import javax.microedition.lcdui.Display; import javax.microedition.lcdui.Displayable; import javax.microedition.lcdui.Form; import javax.microedition.lcdui.Screen; import javax.microedition.midlet.MIDlet; import javax.microedition.midlet.MIDletStateChangeException; import net.rim.device.api.ui.Color; import net.rim.device.api.ui.Graphics; public class alertclass extends MIDlet implements CommandListener { private Display display; private Alert alert; private Form form = new Form("Throw Exception"); private Command exit = new Command("Exit", Command.SCREEN, 1); //public static void main(String[] args) //{ //} private boolean exitFlag = false; public alertclass(){ display = Display.getDisplay(this); form.addCommand(exit); form.setCommandListener(this); } protected void destroyApp(boolean unconditional) throws MIDletStateChangeException { // TODO Auto-generated method stub if (unconditional == false) { throw new MIDletStateChangeException(); } } protected void pauseApp() { // TODO Auto-generated method stub } protected void startApp() throws MIDletStateChangeException { // TODO Auto-generated method stub display.setCurrent(form); } public void commandAction(Command c, Displayable d) { // TODO Auto-generated method stub if (c == exit) { try { if (exitFlag == false) { alert = new Alert("Busy", "Please try again.", null, AlertType.WARNING); alert.setTimeout(Alert.FOREVER); display.setCurrent(alert, form); destroyApp(false); } else { destroyApp(true); notifyDestroyed(); } } catch (Exception exception) { exitFlag = true; } } } }

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  • Java JPA @OneToMany neededs to reciprocate @ManyToOne?

    - by bguiz
    Create Table A ( ID varchar(8), Primary Key(ID) ); Create Table B ( ID varchar(8), A_ID varchar(8), Primary Key(ID), Foreign Key(A_ID) References A(ID) ); Given that I have created two tables using the SQL statements above, and I want to create Entity classes for them, for the class B, I have these member attributes: @Id @Column(name = "ID", nullable = false, length = 8) private String id; @JoinColumn(name = "A_ID", referencedColumnName = "ID", nullable = false) @ManyToOne(optional = false) private A AId; In class A, do I need to reciprocate the many-to-one relationship? @Id @Column(name = "ID", nullable = false, length = 8) private String id; @OneToMany(cascade = CascadeType.ALL, mappedBy = "AId") private List<B> BList; //<-- Is this attribute necessary? Is it a necessary or a good idea to have a reciprocal @OneToMany for the @ManyToOne? If I make the design decision to leave out the @OneToMany annotated attribute now, will come back to bite me further down.

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  • Generic class for performing mass-parallel queries. Feedback?

    - by Aaron
    I don't understand why, but there appears to be no mechanism in the client library for performing many queries in parallel for Windows Azure Table Storage. I've created a template class that can be used to save considerable time, and you're welcome to use it however you wish. I would appreciate however, if you could pick it apart, and provide feedback on how to improve this class. public class AsyncDataQuery<T> where T: new() { public AsyncDataQuery(bool preserve_order) { m_preserve_order = preserve_order; this.Queries = new List<CloudTableQuery<T>>(1000); } public void AddQuery(IQueryable<T> query) { var data_query = (DataServiceQuery<T>)query; var uri = data_query.RequestUri; // required this.Queries.Add(new CloudTableQuery<T>(data_query)); } /// <summary> /// Blocking but still optimized. /// </summary> public List<T> Execute() { this.BeginAsync(); return this.EndAsync(); } public void BeginAsync() { if (m_preserve_order == true) { this.Items = new List<T>(Queries.Count); for (var i = 0; i < Queries.Count; i++) { this.Items.Add(new T()); } } else { this.Items = new List<T>(Queries.Count * 2); } m_wait = new ManualResetEvent(false); for (var i = 0; i < Queries.Count; i++) { var query = Queries[i]; query.BeginExecuteSegmented(callback, i); } } public List<T> EndAsync() { m_wait.WaitOne(); return this.Items; } private List<T> Items { get; set; } private List<CloudTableQuery<T>> Queries { get; set; } private bool m_preserve_order; private ManualResetEvent m_wait; private int m_completed = 0; private void callback(IAsyncResult ar) { int i = (int)ar.AsyncState; CloudTableQuery<T> query = Queries[i]; var response = query.EndExecuteSegmented(ar); if (m_preserve_order == true) { // preserve ordering only supports one result per query this.Items[i] = response.Results.First(); } else { // add any number of items this.Items.AddRange(response.Results); } if (response.HasMoreResults == true) { // more data to pull query.BeginExecuteSegmented(response.ContinuationToken, callback, i); return; } m_completed = Interlocked.Increment(ref m_completed); if (m_completed == Queries.Count) { m_wait.Set(); } } }

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  • Windows Forms application C# | Sending Tweet

    - by Andrew Craswell
    I've been able to get my Twitter web app working just fine, but I've recently decided to add Tweeting functionality from a Windows Form, but I'm having no luck sending tweets. No errors are thrown or anything. Mind looking over my code? using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; using TweetSharp; namespace TwitterAdvirtiser { public partial class Form1 : Form { private string cKey = "xxx"; private string cSecret = "xxx"; private string oToken = "xxx"; private string aToken = "xxx"; public Form1() { InitializeComponent(); OnStart(); } private void OnStart() { //Authenticate with Twitter TwitterService service = new TwitterService(cKey, cSecret); service.AuthenticateWith(oToken, aToken); service.SendTweet("testing"); } } } It seems like I'm authenticating just fine, I can walk through debug mode and see all my details in the TwitterUser structure, and yet my tweets never show up on my feed. Whats up? By the way, I'm using Visual Studios 2010, and .NET 4.0. I have verified that the oToken and aToken strings have my developer tokens.

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  • Calling web service from seems to hang

    - by anothershrubery
    I am trying to call an asmx web service from an Android app. Just literally started some Android development today. I've been following various solutions I have found on the net and on here and it seems it is more difficult than anticipated. I have tried various solutions and using KSoap2 seems to be the easiest way to implement this, well it would be if I could get it working. I have the following code which works up until a point: private class CallWebService extends AsyncTask<Void, Void, Void> { private static final String SOAP_ACTION = "http://tempuri.org/GetUser"; private static final String METHOD_NAME = "GetUser"; private static final String NAMESPACE = "http://tempuri.org/"; private static final String URL = "http://160.10.1.79:59315/Service1.asmx"; TextView tv; @Override protected Void doInBackground(Void... params) { tv=(TextView)findViewById(R.id.txtMessage); try { SoapObject request = new SoapObject(NAMESPACE, METHOD_NAME); SoapSerializationEnvelope envelope = new SoapSerializationEnvelope(SoapEnvelope.VER11); envelope.dotNet=true; envelope.setOutputSoapObject(request); HttpTransportSE androidHttpTransport = new HttpTransportSE(URL); androidHttpTransport.call(SOAP_ACTION, envelope); Object result = (Object)envelope.getResponse(); tv.setText(result.toString()); } catch (Exception e) { tv.setText(e.getMessage()); } return null; } } It seems to hang at the line androidHttpTransport.call(SOAP_ACTION, envelope); Any ideas why? Is this the correct approach? Should I be looking in another direction?

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  • Invalid Cross-Thread Operations from BackgroundWorker2_RunWorkerCompleted in C#

    - by Jim Fell
    Hello. I'm getting an error that does not make sense. Cross-thread operation not valid: Control 'buttonOpenFile' accessed from a thread other than the thread it was created on. In my application, the UI thread fires off backgroundWorker1, which when almost complete fires off backgroundWorker2 and waits for it to complete. backgroundWorker1 waits for backgroundWorker2 to complete, before it completes. AutoResetEvent variables are used to flag when each of the workers complete. In backgroundWorker2_RunWorkerComplete a function is called that resets the form controls. It is in this ResetFormControls() function where the exception is thrown. I thought it was safe to modify form controls in the RunWorkerCompleted function. Both background workers are instantiated from the UI thread. Here is a greatly summarized version of what I am doing: AutoResetEvent evtProgrammingComplete_c = new AutoResetEvent(false); AutoResetEvent evtResetComplete_c = new AutoResetEvent(false); private void ResetFormControls() { toolStripProgressBar1.Enabled = false; toolStripProgressBar1.RightToLeftLayout = false; toolStripProgressBar1.Value = 0; buttonInit.Enabled = true; buttonOpenFile.Enabled = true; // Error occurs here. buttonProgram.Enabled = true; buttonAbort.Enabled = false; buttonReset.Enabled = true; checkBoxPeripheryModule.Enabled = true; checkBoxVerbose.Enabled = true; comboBoxComPort.Enabled = true; groupBoxToolSettings.Enabled = true; groupBoxNodeSettings.Enabled = true; } private void buttonProgram_Click(object sender, EventArgs e) { while (backgroundWorkerProgram.IsBusy) backgroundWorkerProgram.CancelAsync(); backgroundWorkerProgram.RunWorkerAsync(); } private void backgroundWorkerProgram_DoWork(object sender, DoWorkEventArgs e) { // Does a bunch of stuff... if (tProgramStat_c == eProgramStat_t.DONE) { tProgramStat_c = eProgramStat_t.RESETTING; while (backgroundWorkerReset.IsBusy) backgroundWorkerReset.CancelAsync(); backgroundWorkerReset.RunWorkerAsync(); evtResetComplete_c.WaitOne(LONG_ACK_WAIT * 2); if (tResetStat_c == eResetStat_t.COMPLETED) tProgramStat_c = eProgramStat_t.DONE; } } private void backgroundWorkerProgram_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) { // Updates form to report complete. No problems here. evtProgrammingComplete_c.Set(); backgroundWorkerProgram.Dispose(); } private void backgroundWorkerReset_DoWork(object sender, DoWorkEventArgs e) { // Does a bunch of stuff... if (tResetStat_c == eResetStat_t.COMPLETED) if (tProgramStat_c == eProgramStat_t.RESETTING) evtProgrammingComplete_c.WaitOne(); } private void backgroundWorkerReset_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) { CloseAllComms(); ResetFormControls(); evtResetComplete_c.Set(); backgroundWorkerReset.Dispose(); } Any thoughts or suggestions you may have would be appreciated. I am using Microsoft Visual C# 2008 Express Edition. Thanks.

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  • How do I Insert Record MVVM through WCF

    - by DG KOL
    Hello, I’m new in MVVM Pattern (Using Galasoft MVVM Light toolkit). I’ve created a Test Project where I want to fetch some records from Database through WCF. This is working fine but I’ve failed to insert new record from View; Here is My Code: Database Table Name: TestUser (First Name, LastName) WCF (NWCustomer) Two Methods Public List<TestUser> GetAllUsers() [“LINQ2SQL Operation”] Public bool AddUser(TestUser testuser) Public bool AddUser(TestUser testuser) { try { using (DBDataContext db = new DBDataContext()) { TestUser test = new TestUser() { FirstName = testuser.FirstName, LastName = testuser.LastName }; db.TestUser.InsertOnSubmit(test); db.SubmitChanges(); } } catch (Exception ex) { return false; } return true; } Silverlight Project MODEL consists ITestUserService.cs TestUserService.cs public void AddTestTable(TestTableViewModel testuser, Action<bool> callback) { NWCustomerClient client = new NWCustomerClient("BasicHttpBinding_NWCustomer"); client.AddTestUserCompleted += (s, e) => { var userCallback = e.UserState as Action<bool>; if (userCallback == null) { return; } if (e.Error == null) { userCallback(e.Result); return; } userCallback(false); }; client.AddTestUserAsync(testuser.Model); } VIEWMODEL TestUserViewModel public TestUser User { get; private set; } public const string DirtyVisibilityPropertyName = "DirtyVisibility"; private Visibility _dirty = Visibility.Collapsed; public Visibility DirtyVisibility { get { return _dirty; } set { if (_dirty == value) { return; } _dirty = value; RaisePropertyChanged(DirtyVisibilityPropertyName); } } public TestUserViewModel (TestUser user) { User = user; user.PropertyChanged += (s, e) => { DirtyVisibility = Visibility.Visible; }; } MainViewModel public ObservableCollection<TestUserViewModel> TestTables { get; private set; } public const string ErrorMessagePropertyName = "ErrorMessage"; private string _errorMessage = string.Empty; public string ErrorMessage { get { return _errorMessage; } set { if (_errorMessage == value) { return; } _errorMessage = value; RaisePropertyChanged(ErrorMessagePropertyName); } } private ITestUserService _service; public RelayCommand< TestUserViewModel> AddTestUserRecord { get; private set; } public MainTestTableViewModel (ICustomerService service) { _service = service; TestTables = new ObservableCollection<TestTableViewModel>(); service.GetAllTestTable(HandleResult); } private void HandleResult(IEnumerable<TestTable> result, Exception ex) { TestTables.Clear(); if (ex != null) { //Error return; } if (result == null) { return; } foreach (var test in result) { var table = new TestTableViewModel(test); TestTables.Add(table); } } XAML <Grid x:Name="LayoutRoot"> <StackPanel> <TextBox Text="FirstName" /> <TextBox Text="LastName" /> <Button Content="Add Record" Command="{Binding AddTestUserRecord}" /> </StackPanel> </Grid> I want to add records into TestTable (Database Table). How do I insert record? In XAML two text box and a button control is present. Thanking you. DG

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  • Problem persisting inheritance tree

    - by alaiseca
    I have a problem trying to map an inheritance tree. A simplified version of my model is like this: @MappedSuperclass @Embeddable public class BaseEmbedded implements Serializable { @Column(name="BE_FIELD") private String beField; // Getters and setters follow } @MappedSuperclass @Embeddable public class DerivedEmbedded extends BaseEmbedded { @Column(name="DE_FIELD") private String deField; // Getters and setters follow } @MappedSuperclass public abstract class BaseClass implements Serializable { @Embedded protected BaseEmbedded embedded; public BaseClass() { this.embedded = new BaseEmbedded(); } // Getters and setters follow } @Entity @Table(name="MYTABLE") @Inheritance(strategy=InheritanceType.SINGLE_TABLE) @DiscriminatorColumn(name="TYPE", discriminatorType=DiscriminatorType.STRING) public class DerivedClass extends BaseClass { @Id @Column(name="ID", nullable=false) private Long id; @Column(name="TYPE", nullable=false, insertable=false, updatable=false) private String type; public DerivedClass() { this.embedded = new DerivedClass(); } // Getters and setters follow } @Entity @DiscriminatorValue("A") public class DerivedClassA extends DerivedClass { @Embeddable public static NestedClassA extends DerivedEmbedded { @Column(name="FIELD_CLASS_A") private String fieldClassA; } public DerivedClassA() { this.embedded = new NestedClassA(); } // Getters and setters follow } @Entity @DiscriminatorValue("B") public class DerivedClassB extends DerivedClass { @Embeddable public static NestedClassB extends DerivedEmbedded { @Column(name="FIELD_CLASS_B") private String fieldClassB; } public DerivedClassB() { this.embedded = new NestedClassB(); } // Getters and setters follow } At Java level, this model is working fine, and I believe is the appropriate one. My problem comes up when it's time to persist an object. At runtime, I can create an object which could be an instance of DerivedClass, DerivedClassA or DerivedClassB. As you can see, each one of the derived classes introduces a new field which only makes sense for that specific derived class. All the classes share the same physical table in the database. If I persist an object of type DerivedClass, I expect fields BE_FIELD, DE_FIELD, ID and TYPE to be persisted with their values and the remaining fields to be null. If I persist an object of type DerivedClass A, I expect those same fields plus the FIELD_CLASS_A field to be persisted with their values and field FIELD_CLASS_B to be null. Something equivalent for an object of type DerivedClassB. Since the @Embedded annotation is at the BaseClass only, Hibernate is only persisting the fields up to that level in the tree. I don't know how to tell Hibernate that I want to persist up to the appropriate level in the tree, depending on the actual type of the embedded property. I cannot have another @Embedded property in the subclasses since this would duplicate data that is already present in the superclass and would also break the Java model. I cannot declare the embedded property to be of a more specific type either, since it's only at runtime when the actual object is created and I don't have a single branch in the hierarchy. Is it possible to solve my problem? Or should I resignate myself to accept that there is no way to persist the Java model as it is? Any help will be greatly appreciated.

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  • Concurrency problem with arrays (Java)

    - by Johannes
    For an algorithm I'm working on I tried to develop a blacklisting mechanism that can blacklist arrays in a specific way: If "1, 2, 3" is blacklisted "1, 2, 3, 4, 5" is also considered blacklisted. I'm quite happy with the solution I've come up with so far. But there seem to be some serious problems when I access a blacklist from multiple threads. The method "contains" (see code below) sometimes returns true, even if an array is not blacklisted. This problem does not occur if I only use one thread, so it most likely is a concurrency problem. I've tried adding some synchronization, but it didn't change anything. I also tried some slightly different implementations using java.util.concurrent classes. Any ideas on how to fix this? public class Blacklist { private static final int ARRAY_GROWTH = 10; private final Node root = new Node(); private static class Node{ private volatile Node[] childNodes = new Node[ARRAY_GROWTH]; private volatile boolean blacklisted = false; public void blacklist(){ this.blacklisted = true; this.childNodes = null; } } public void add(final int[] array){ synchronized (root) { Node currentNode = this.root; for(final int edge : array){ if(currentNode.blacklisted) return; else if(currentNode.childNodes.length <= edge) { currentNode.childNodes = Arrays.copyOf(currentNode.childNodes, edge + ARRAY_GROWTH); } if(currentNode.childNodes[edge] == null) { currentNode.childNodes[edge] = new Node(); } currentNode = currentNode.childNodes[edge]; } currentNode.blacklist(); } } public boolean contains(final int[] array){ synchronized (root) { Node currentNode = this.root; for(final int edge : array){ if(currentNode.blacklisted) return true; else if(currentNode.childNodes.length <= edge || currentNode.childNodes[edge] == null) return false; currentNode = currentNode.childNodes[edge]; } return currentNode.blacklisted; } } }

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  • VB.NET generates properties in the release build

    - by dattebayo
    I have a form and i drag and drop a control in VB.NET. I have a line say, private WithEvents radioButton RadioButton Also, I have a handler like, private void click(.....) Handles radioButton.Click { ... } Now, When I build this is .NET 3.5 in release mode, and see the generated code in reflector tool, the code is something like, Private Overridable Property radioButton As RadioButton . . . <AccessedThroughProperty("radioButton")> _ Private _radioButton As RadioButton Can someone tell me what is going on here? And how do I avoid the generation of new properties and fields? -datte

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  • Using static variables for Strings

    - by Vivart
    below content is taken from Best practice: Writing efficient code but i didn't understand why private static String x = "example"; faster than private static final String x ="example"; Can anybody explain this. Using static variables for Strings When you define static fields (also called class fields) of type String, you can increase application speed by using static variables (not final) instead of constants (final). The opposite is true for primitive data types, such as int. For example, you might create a String object as follows: private static final String x = "example"; For this static constant (denoted by the final keyword), each time that you use the constant, a temporary String instance is created. The compiler eliminates "x" and replaces it with the string "example" in the bytecode, so that the BlackBerry® Java® Virtual Machine performs a hash table lookup each time that you reference "x". In contrast, for a static variable (no final keyword), the String is created once. The BlackBerry JVM performs the hash table lookup only when it initializes "x", so access is faster. private static String x = "example"; You can use public constants (that is, final fields), but you must mark variables as private.

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  • Java: Comparing a class with another within that class using a my own .equals

    - by user1670252
    I am making a method .equals replacing the equals method used. It accepts a object. I want it to check if that object equals the class that runs the .equals class. I know I want to compare all the private methods I have to that object. Is there a way to do this without making another private class to get the private variables from the object? How do I do this to compare equality not identity? I am stuck on this. Do i have to use == to compare? Also looking online i see others use recursion. If this is the way i have to do it can you show and explain it to me? so an example i have public boolean equals(Object o) { this is in a class we will call bobtheBuilder (first thing to pop in my head) I want to check if the object o is equal to the class he has private object array and a private int. I assume I want to check if the array and int of this class equal the array and int of the object.

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  • jsf annotations

    - by Andrew Bucknell
    I've created an address bean and I want to use it twice - once for street address and once for mailing address. I can achieve this using faces config as per the below, but I'm wondering if I can do this via annotations. e.g. put @ManagedBean(name="StreetAddress") and @ManagedBean(name="MailingAddress") on the same class? I feel like I am missing something obvious here but I'm not sure what. <managed-bean> <managed-bean-name>MailingAddress</managed-bean-name> <managed-bean-class>com.leetb.jsf_ex1.model.AddressBean</managed-bean-class> <managed-bean-scope>session</managed-bean-scope> <map-entries/> </managed-bean> <managed-bean> <managed-bean-name>StreetAddress</managed-bean-name> <managed-bean-class>com.leetb.jsf_ex1.model.AddressBean</managed-bean-class> <managed-bean-scope>session</managed-bean-scope> <map-entries/> </managed-bean> public class AddressBean { private String line_one; private String line_two; private String suburb; private String state; private String postcode; /* getters and setters snipped */ }

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  • Java program grading

    - by pasito15
    I've been working on this program for hours and I can't figure out how to get the program to actually print the grades from the scores Text file public class Assign7{ private double finalScore; private double private_quiz1; private double private_quiz2; private double private_midTerm; private double private_final; private final char grade; public Assign7(double finalScore){ private_quiz1 = 1.25; private_quiz2 = 1.25; private_midTerm = 0.25; private_final = 0.50; if (finalScore >= 90) { grade = 'A'; } else if (finalScore >= 80) { grade = 'B'; } else if (finalScore >= 70) { grade = 'C'; } else if (finalScore>= 60) { grade = 'D'; } else { grade = 'F'; } } public String toString(){ return finalScore+":"+private_quiz1+":"+private_quiz2+":"+private_midTerm+":"+private_final; } } this code compiles as well as this one import java.util.*; import java.io.*; public class Assign7Test{ public static void main(String[] args)throws Exception{ int q1,q2; int m = 0; int f = 0; int Record ; String name; Scanner myIn = new Scanner( new File("scores.txt") ); System.out.println( myIn.nextLine() +" avg "+"letter"); while( myIn.hasNext() ){ name = myIn.next(); q1 = myIn.nextInt(); q2 = myIn.nextInt(); m = myIn.nextInt(); f = myIn.nextInt(); Record myR = new Record( name, q1,q2,m,f); System.out.println(myR); } } public static class Record { public Record() { } public Record(String name, int q1, int q2, int m, int f) { } } } once a compile the code i get this which dosent exactly compute the numbers I have in the scores.txt Name quiz1 quiz2 midterm final avg letter Assign7Test$Record@4bcc946b Assign7Test$Record@642423 Exception in thread "main" java.until.InputMismatchException at java.until.Scanner.throwFor(Unknown Source) at java.until.Scanner.next(Unknown Source) at java.until.Scanner.nextInt(Unknown Source) at java.until.Scanner.nextInt(Unknown Source) at Assign7Test.main(Assign7Test.java:25)

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  • When to use @Singleton in a Jersey resource

    - by dexter
    I have a Jersey resource that access the database. Basically it opens a database connection in the initialization of the resource. Performs queries on the resource's methods. I have observed that when I do not use @Singleton, the database is being open at each request. And we know opening a connection is really expensive right? So my question is, should I specify that the resource be singleton or is it really better to keep it at per request especially when the resource is connecting to the database? My resource code looks like this: //Use @Singleton here or not? @Path(/myservice/) public class MyResource { private ResponseGenerator responser; private Log logger = LogFactory.getLog(MyResource.class); public MyResource() { responser = new ResponseGenerator(); } @GET @Path("/clients") public String getClients() { logger.info("GETTING LIST OF CLIENTS"); return responser.returnClients(); } ... // some more methods ... } And I connect to the database using a code similar to this: public class ResponseGenerator { private Connection conn; private PreparedStatement prepStmt; private ResultSet rs; public ResponseGenerator(){ Class.forName("org.h2.Driver"); conn = DriverManager.getConnection("jdbc:h2:testdb"); } public String returnClients(){ String result; try{ prepStmt = conn.prepareStatement("SELECT * FROM hosts"); rs = prepStmt.executeQuery(); ... //do some processing here ... } catch (SQLException se){ logger.warn("Some message"); } finally { rs.close(); prepStmt.close(); // should I also close the connection here (in every method) if I stick to per request // and add getting of connection at the start of every method // conn.close(); } return result } ... // some more methods ... } Some comments on best practices for the code will also be helpful.

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  • Two entities with @ManyToOne joins the same table

    - by Ivan Yatskevich
    I have the following entities Student @Entity public class Student implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; //getter and setter for id } Teacher @Entity public class Teacher implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; //getter and setter for id } Task @Entity public class Task implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; @ManyToOne(optional = false) @JoinTable(name = "student_task", inverseJoinColumns = { @JoinColumn(name = "student_id") }) private Student author; @ManyToOne(optional = false) @JoinTable(name = "student_task", inverseJoinColumns = { @JoinColumn(name = "teacher_id") }) private Teacher curator; //getters and setters } Consider that author and curator are already stored in DB and both are in the attached state. I'm trying to persist my Task: Task task = new Task(); task.setAuthor(author); task.setCurator(curator); entityManager.persist(task); Hibernate executes the following SQL: insert into student_task (teacher_id, id) values (?, ?) which, of course, leads to null value in column "student_id" violates not-null constraint Can anyone explain this issue and possible ways to resolve it?

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  • Android Dev: The constructor Intent(new View.OnClickListener(){}, Class<DrinksTwitter>) is undefined

    - by Malcolm Woods Spark
    package com.android.drinksonme; import android.app.Activity; import android.content.Intent; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.EditText; import android.widget.TextView; public class Screen2 extends Activity { // Declare our Views, so we can access them later private EditText etUsername; private EditText etPassword; private Button btnLogin; private Button btnSignUp; private TextView lblResult; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); // Get the EditText and Button References etUsername = (EditText)findViewById(R.id.username); etPassword = (EditText)findViewById(R.id.password); btnLogin = (Button)findViewById(R.id.login_button); btnSignUp = (Button)findViewById(R.id.signup_button); lblResult = (TextView)findViewById(R.id.result); // Set Click Listener btnLogin.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { // Check Login String username = etUsername.getText().toString(); String password = etPassword.getText().toString(); if(username.equals("test") && password.equals("test")){ final Intent i = new Intent(this, DrinksTwitter.class); //error on this line startActivity(i); // lblResult.setText("Login successful."); } else { lblResult.setText("Invalid username or password."); } } }); final Intent k = new Intent(Screen2.this, SignUp.class); btnSignUp.setOnClickListener(new OnClickListener() { public void onClick(View v) { startActivity(k); } }); } }

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  • toString() Method question

    - by cdominguez13
    I've been working on this assignemnt here's code: public class Student { private String fname; private String lname; private String studentId; private double gpa; public Student(String studentFname,String studentLname,String stuId,double studentGpa) { fname = studentFname; lname = studentLname; studentId = stuId; gpa = studentGpa; } public double getGpa() { return gpa; } public String getStudentId() { return studentId; } public String getName() { return lname + ", " + fname; } public void setGpa(double gpaReplacement) { if (gpaReplacement >= 0.0 && gpaReplacement <= 4.0) gpa = gpaReplacement; else System.out.println("Invalid GPA! Please try again."); System.exit(0); } } Now I need to create a toString() method that returns a String formatted something like this: Name: Wilson, Mary Ann ID number: 12345 GPA: 3.5

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  • How are classes more secure than structures ?

    - by Asad Hanif
    Structure's member are public by default ans class's members are private by default. We can access private data members through a proper channel (using member function). If we have access to member functions we can read/write data in private data member, so how it is secure...we are accessing it and we are changing data too.....

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