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  • Why does Java allow to implement different interfaces, each containing a method with the same signature?

    - by Software Engeneering Learner
    I've recently found that I can have two interfaces containing method with the same signature as a method in the other interface. And then I can have an interface or class that implements both of that interfaces. So the descendant class/interface has implicitly implements two different methods as a one method. Why is this allowed in Java? I can see a numerous problems that arises from that. Even eclipse only can find out about implementations for only one interface method, but for the second one it doesn't show any implementations at all. Also I believe there would be problems with automatic refactoring, like when you would like to change the signature of the method in one of the interfaces and IDE won't be able to correctly change that signature in all implementations, as they implement two different interfaces and how will IDE know what interface method it implementation descends. Why don't just make a compiler error like 'interfaces method names clashes' or something like that?

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  • How to Implement Project Type "Copy", "Move", "Rename", and "Delete"

    - by Geertjan
    You've followed the NetBeans Project Type Tutorial and now you'd like to let the user copy, move, rename, and delete the projects conforming to your project type. When they right-click a project, they should see the relevant menu items and those menu items should provide dialogs for user interaction, followed by event handling code to deal with the current operation. Right now, at the end of the tutorial, the "Copy" and "Delete" menu items are present but disabled, while the "Move" and "Rename" menu items are absent: The NetBeans Project API provides a built-in mechanism out of the box that you can leverage for project-level "Copy", "Move", "Rename", and "Delete" actions. All the functionality is there for you to use, while all that you need to do is a bit of enablement and configuration, which is described below. To get started, read the following from the NetBeans Project API: http://bits.netbeans.org/dev/javadoc/org-netbeans-modules-projectapi/org/netbeans/spi/project/ActionProvider.html http://bits.netbeans.org/dev/javadoc/org-netbeans-modules-projectapi/org/netbeans/spi/project/CopyOperationImplementation.html http://bits.netbeans.org/dev/javadoc/org-netbeans-modules-projectapi/org/netbeans/spi/project/MoveOrRenameOperationImplementation.html http://bits.netbeans.org/dev/javadoc/org-netbeans-modules-projectapi/org/netbeans/spi/project/DeleteOperationImplementation.html Now, let's do some work. For each of the menu items we're interested in, we need to do the following: Provide enablement and invocation handling in an ActionProvider implementation. Provide appropriate OperationImplementation classes. Add the new classes to the Project Lookup. Make the Actions visible on the Project Node. Run the application and verify the Actions work as you'd like. Here we go: Create an ActionProvider. Here you specify the Actions that should be supported, the conditions under which they should be enabled, and what should happen when they're invoked, using lots of default code that lets you reuse the functionality provided by the NetBeans Project API: class CustomerActionProvider implements ActionProvider { @Override public String[] getSupportedActions() { return new String[]{ ActionProvider.COMMAND_RENAME, ActionProvider.COMMAND_MOVE, ActionProvider.COMMAND_COPY, ActionProvider.COMMAND_DELETE }; } @Override public void invokeAction(String string, Lookup lkp) throws IllegalArgumentException { if (string.equalsIgnoreCase(ActionProvider.COMMAND_RENAME)) { DefaultProjectOperations.performDefaultRenameOperation( CustomerProject.this, ""); } if (string.equalsIgnoreCase(ActionProvider.COMMAND_MOVE)) { DefaultProjectOperations.performDefaultMoveOperation( CustomerProject.this); } if (string.equalsIgnoreCase(ActionProvider.COMMAND_COPY)) { DefaultProjectOperations.performDefaultCopyOperation( CustomerProject.this); } if (string.equalsIgnoreCase(ActionProvider.COMMAND_DELETE)) { DefaultProjectOperations.performDefaultDeleteOperation( CustomerProject.this); } } @Override public boolean isActionEnabled(String command, Lookup lookup) throws IllegalArgumentException { if ((command.equals(ActionProvider.COMMAND_RENAME))) { return true; } else if ((command.equals(ActionProvider.COMMAND_MOVE))) { return true; } else if ((command.equals(ActionProvider.COMMAND_COPY))) { return true; } else if ((command.equals(ActionProvider.COMMAND_DELETE))) { return true; } return false; } } Importantly, to round off this step, add "new CustomerActionProvider()" to the "getLookup" method of the project. If you were to run the application right now, all the Actions we're interested in would be enabled (if they are visible, as described in step 4 below) but when you invoke any of them you'd get an error message because each of the DefaultProjectOperations above looks in the Lookup of the Project for the presence of an implementation of a class for handling the operation. That's what we're going to do in the next step. Provide Implementations of Project Operations. For each of our operations, the NetBeans Project API lets you implement classes to handle the operation. The dialogs for interacting with the project are provided by the NetBeans project system, but what happens with the folders and files during the operation can be influenced via the operations. Below are the simplest possible implementations, i.e., here we assume we want nothing special to happen. Each of the below needs to be in the Lookup of the Project in order for the operation invocation to succeed. private final class CustomerProjectMoveOrRenameOperation implements MoveOrRenameOperationImplementation { @Override public List<FileObject> getMetadataFiles() { return new ArrayList<FileObject>(); } @Override public List<FileObject> getDataFiles() { return new ArrayList<FileObject>(); } @Override public void notifyRenaming() throws IOException { } @Override public void notifyRenamed(String nueName) throws IOException { } @Override public void notifyMoving() throws IOException { } @Override public void notifyMoved(Project original, File originalPath, String nueName) throws IOException { } } private final class CustomerProjectCopyOperation implements CopyOperationImplementation { @Override public List<FileObject> getMetadataFiles() { return new ArrayList<FileObject>(); } @Override public List<FileObject> getDataFiles() { return new ArrayList<FileObject>(); } @Override public void notifyCopying() throws IOException { } @Override public void notifyCopied(Project prjct, File file, String string) throws IOException { } } private final class CustomerProjectDeleteOperation implements DeleteOperationImplementation { @Override public List<FileObject> getMetadataFiles() { return new ArrayList<FileObject>(); } @Override public List<FileObject> getDataFiles() { return new ArrayList<FileObject>(); } @Override public void notifyDeleting() throws IOException { } @Override public void notifyDeleted() throws IOException { } } Also make sure to put the above methods into the Project Lookup. Check the Lookup of the Project. The "getLookup()" method of the project should now include the classes you created above, as shown in bold below: @Override public Lookup getLookup() { if (lkp == null) { lkp = Lookups.fixed(new Object[]{ this, new Info(), new CustomerProjectLogicalView(this), new CustomerCustomizerProvider(this), new CustomerActionProvider(), new CustomerProjectMoveOrRenameOperation(), new CustomerProjectCopyOperation(), new CustomerProjectDeleteOperation(), new ReportsSubprojectProvider(this), }); } return lkp; } Make Actions Visible on the Project Node. The NetBeans Project API gives you a number of CommonProjectActions, including for the actions we're dealing with. Make sure the items in bold below are in the "getActions" method of the project node: @Override public Action[] getActions(boolean arg0) { return new Action[]{ CommonProjectActions.newFileAction(), CommonProjectActions.copyProjectAction(), CommonProjectActions.moveProjectAction(), CommonProjectActions.renameProjectAction(), CommonProjectActions.deleteProjectAction(), CommonProjectActions.customizeProjectAction(), CommonProjectActions.closeProjectAction() }; } Run the Application. When you run the application, you should see this: Let's now try out the various actions: Copy. When you invoke the Copy action, you'll see the dialog below. Provide a new project name and location and then the copy action is performed when the Copy button is clicked below: The message you see above, in red, might not be relevant to your project type. When you right-click the application and choose Branding, you can find the string in the Resource Bundles tab, as shown below: However, note that the message will be shown in red, no matter what the text is, hence you can really only put something like a warning message there. If you have no text at all, it will also look odd.If the project has subprojects, the copy operation will not automatically copy the subprojects. Take a look here and here for similar more complex scenarios. Move. When you invoke the Move action, the dialog below is shown: Rename. The Rename Project dialog below is shown when you invoke the Rename action: I tried it and both the display name and the folder on disk are changed. Delete. When you invoke the Delete action, you'll see this dialog: The checkbox is not checkable, in the default scenario, and when the dialog above is confirmed, the project is simply closed, i.e., the node hierarchy is removed from the application. However, if you truly want to let the user delete the project on disk, pass the Project to the DeleteOperationImplementation and then add the children of the Project you want to delete to the getDataFiles method: private final class CustomerProjectDeleteOperation implements DeleteOperationImplementation { private final CustomerProject project; private CustomerProjectDeleteOperation(CustomerProject project) { this.project = project; } @Override public List<FileObject> getDataFiles() { List<FileObject> files = new ArrayList<FileObject>(); FileObject[] projectChildren = project.getProjectDirectory().getChildren(); for (FileObject fileObject : projectChildren) { addFile(project.getProjectDirectory(), fileObject.getNameExt(), files); } return files; } private void addFile(FileObject projectDirectory, String fileName, List<FileObject> result) { FileObject file = projectDirectory.getFileObject(fileName); if (file != null) { result.add(file); } } @Override public List<FileObject> getMetadataFiles() { return new ArrayList<FileObject>(); } @Override public void notifyDeleting() throws IOException { } @Override public void notifyDeleted() throws IOException { } } Now the user will be able to check the checkbox, causing the method above to be called in the DeleteOperationImplementation: Hope this answers some questions or at least gets the discussion started. Before asking questions about this topic, please take the steps above and only then attempt to apply them to your own scenario. Useful implementations to look at: http://kickjava.com/src/org/netbeans/modules/j2ee/clientproject/AppClientProjectOperations.java.htm https://kenai.com/projects/nbandroid/sources/mercurial/content/project/src/org/netbeans/modules/android/project/AndroidProjectOperations.java

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  • Multi-threaded JOGL Problem

    - by moeabdol
    I'm writing a simple OpenGL application in Java that implements the Monte Carlo method for estimating the value of PI. The method is pretty easy. Simply, you draw a circle inside a unit square and then plot random points over the scene. Now, for each point that is inside the circle you increment the counter for in points. After determining for all the random points wither they are inside the circle or not you divide the number of in points over the total number of points you have plotted all multiplied by 4 to get an estimation of PI. It goes something like this PI = (inPoints / totalPoints) * 4. This is because mathematically the ratio of a circle's area to a square's area is PI/4, so when we multiply it by 4 we get PI. My problem doesn't lie in the algorithm itself; however, I'm having problems trying to plot the points as they are being generated instead of just plotting everything at once when the program finishes executing. I want to give the application a sense of real-time display where the user would see the points as they are being plotted. I'm a beginner at OpenGL and I'm pretty sure there is a multi-threading feature built into it. Non the less, I tried to manually create my own thread. Each worker thread plots one point at a time. Following is the psudo-code: /* this part of the code exists in display() method in MyCanvas.java which extends GLCanvas and implements GLEventListener */ // main loop for(int i = 0; i < number_of_points; i++){ RandomGenerator random = new RandomGenerator(); float x = random.nextFloat(); float y = random.nextFloat(); Thread pointThread = new Thread(new PointThread(x, y)); } gl.glFlush(); /* this part of the code exists in run() method in PointThread.java which implements Runnable */ void run(){ try{ gl.glPushMatrix(); gl.glBegin(GL2.GL_POINTS); if(pointIsIn) gl.glColor3f(1.0f, 0.0f, 0.0f); // red point else gl.glColor3f(0.0f, 0.0f, 1.0f); // blue point gl.glVertex3f(x, y, 0.0f); // coordinates gl.glEnd(); gl.glPopMatrix(); }catch(Exception e){ } } I'm not sure if my approach to solving this issue is correct. I hope you guys can help me out. Thanks.

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  • Should I implement an interface directly or have the superclass do it?

    - by c_maker
    Is there a difference between public class A extends AbstractB implements C {...} versus... public class A extends AbstractB {...} AbstractB implements C {...} I understand that in both cases, class A will end up conforming to the interface. In the second case, AbstractB can provide implementation for interface methods in C. Is that the only difference? If I do NOT want to provide an implementation for any of the interface methods in AbstractB, which style should I be using? Does using one or the other have some hidden 'documentation' purpose?

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  • @OnStart & @OnStop

    - by Geertjan
    In applications based on NetBeans Platform 7.2, you'll be able to replace all your ModuleInstall classes with this code: import org.openide.modules.OnStart; import org.openide.modules.OnStop; @OnStart public final class Installer implements Runnable { @Override public void run() { System.out.println("enable something..."); } @OnStop public static final class Down implements Runnable { @Override public void run() { System.out.println("disable something..."); } } } Build the module and the annotations result in named services, thanks to @NamedServiceDefinition: Aside from no longer needing to register the ModuleInstall class in the manifest, performance of startup will be enhanced, if you use the above approach: https://netbeans.org/bugzilla/show_bug.cgi?id=200636

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  • What happens if we serialize and deserialize two objects which references to each other?

    - by Seregwethrin
    To make it more clear, this is a quick example: class A implements Serializable { public B b; } class B implements Serializable { public A a; } A a = new A(); B b = new B(); a.b = b; b.a = a; So what happens if we serialize a and b objects into a file and deserialize from that file? I thought we get 4 objects, 2 of each. Identical objects but different instances. But I'm not sure if there's anything else or is it right or wrong. If any technology needed to answer, please think based on Java. Thank you.

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  • Issue allowing custom Xml Serialization/Deserialization on certain types of field

    - by sw1sh
    I've been working with Xml Serialization/Deserialization in .net and wanted a method where the serialization/deserialization process would only be applied to certain parts of an Xml fragment. This is so I can keep certain parts of the fragment in Xml after the deserialization process. To do this I thought it would be best to create a new class (XmlLiteral) that implemented IXmlSerializable and then wrote specific code for handling the IXmlSerializable.ReadXml and IXmlSerializable.WriteXml methods. In my example below this works for Serializing, however during the Deserialization process it fails to run for multiple uses of my XmlLiteral class. In my example below sTest1 gets populated correctly, but sTest2 and sTest3 are empty. I'm guessing I must be going wrong with the following lines but can't figure out why.. Any ideas at all? Private Sub ReadXml(ByVal reader As System.Xml.XmlReader) Implements IXmlSerializable.ReadXml Dim StringType As String = "" If reader.IsEmptyElement OrElse reader.Read() = False Then Exit Sub End If _src = reader.ReadOuterXml() End Sub Full listing: Imports System Imports System.Xml.Serialization Imports System.Xml Imports System.IO Imports System.Text Public Class XmlLiteralExample Inherits System.Web.UI.Page Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load Dim MyObjectInstance As New MyObject MyObjectInstance.aProperty = "MyValue" MyObjectInstance.XmlLiteral1 = New XmlLiteral("<test1>Some Value</test1>") MyObjectInstance.XmlLiteral2 = New XmlLiteral("<test2>Some Value</test2>") MyObjectInstance.XmlLiteral3 = New XmlLiteral("<test3>Some Value</test3>") ' quickly serialize the object to Xml Dim sw As New StringWriter(New StringBuilder()) Dim s As New XmlSerializer(MyObjectInstance.[GetType]()), xmlnsEmpty As New XmlSerializerNamespaces xmlnsEmpty.Add("", "") s.Serialize(sw, MyObjectInstance, xmlnsEmpty) Dim XElement As XElement = XElement.Parse(sw.ToString()) ' XElement reads as the following, so serialization works OK '<MyObject> ' <aProperty>MyValue</aProperty> ' <XmlLiteral1> ' <test1>Some Value</test1> ' </XmlLiteral1> ' <XmlLiteral2> ' <test2>Some Value</test2> ' </XmlLiteral2> ' <XmlLiteral3> ' <test3>Some Value</test3> ' </XmlLiteral3> '</MyObject> ' quickly deserialize the object back to an instance of MyObjectInstance2 Dim MyObjectInstance2 As New MyObject Dim xmlReader As XmlReader, x As XmlSerializer xmlReader = XElement.CreateReader x = New XmlSerializer(MyObjectInstance2.GetType()) MyObjectInstance2 = x.Deserialize(xmlReader) Dim sProperty As String = MyObjectInstance2.aProperty ' equal to "MyValue" Dim sTest1 As String = MyObjectInstance2.XmlLiteral1.Text ' contains <test1>Some Value</test1> Dim sTest2 As String = MyObjectInstance2.XmlLiteral2.Text ' is empty Dim sTest3 As String = MyObjectInstance2.XmlLiteral3.Text ' is empty ' sTest3 and sTest3 should be populated but are not? xmlReader = Nothing End Sub Public Class MyObject Private _aProperty As String Private _XmlLiteral1 As XmlLiteral Private _XmlLiteral2 As XmlLiteral Private _XmlLiteral3 As XmlLiteral Public Property aProperty As String Get Return _aProperty End Get Set(ByVal value As String) _aProperty = value End Set End Property Public Property XmlLiteral1 As XmlLiteral Get Return _XmlLiteral1 End Get Set(ByVal value As XmlLiteral) _XmlLiteral1 = value End Set End Property Public Property XmlLiteral2 As XmlLiteral Get Return _XmlLiteral2 End Get Set(ByVal value As XmlLiteral) _XmlLiteral2 = value End Set End Property Public Property XmlLiteral3 As XmlLiteral Get Return _XmlLiteral3 End Get Set(ByVal value As XmlLiteral) _XmlLiteral3 = value End Set End Property Public Sub New() _XmlLiteral1 = New XmlLiteral _XmlLiteral2 = New XmlLiteral _XmlLiteral3 = New XmlLiteral End Sub End Class <System.Xml.Serialization.XmlRootAttribute(Namespace:="", IsNullable:=False)> _ Public Class XmlLiteral Implements IXmlSerializable Private _src As String Public Property Text() As String Get Return _src End Get Set(ByVal value As String) _src = value End Set End Property Public Sub New() _src = "" End Sub Public Sub New(ByVal Text As String) _src = Text End Sub #Region "IXmlSerializable Members" Private Function GetSchema() As System.Xml.Schema.XmlSchema Implements IXmlSerializable.GetSchema Return Nothing End Function Private Sub ReadXml(ByVal reader As System.Xml.XmlReader) Implements IXmlSerializable.ReadXml Dim StringType As String = "" If reader.IsEmptyElement OrElse reader.Read() = False Then Exit Sub End If _src = reader.ReadOuterXml() End Sub Private Sub WriteXml(ByVal writer As System.Xml.XmlWriter) Implements IXmlSerializable.WriteXml writer.WriteRaw(_src) End Sub #End Region End Class End Class

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  • Android how to get gps location

    - by Faisal khan
    I want to detect location from gps listener and also from network my code is as follows For network location listen locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, WLConstants.DELAY_HOUR, 500.0f, nsl); // where nsl is listener implements LocationListener and for the gps location listen locationManager.requestLocationUpdates( LocationManager.GPS_PROVIDER, WLConstants.DELAY_HOUR, gpsListener .getMinDistance(), gpsListener);// where gps listener implements LocationListener Can we have one listener to listen both rather then launching two different listeners to listen from network and gps???

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  • GetHashCode on null fields?

    - by Shimmy
    How do I deal with null fields in GetHashCode function? Module Module1 Sub Main() Dim c As New Contact Dim hash = c.GetHashCode End Sub Public Class Contact : Implements IEquatable(Of Contact) Public Name As String Public Address As String Public Overloads Function Equals(ByVal other As Contact) As Boolean _ Implements System.IEquatable(Of Contact).Equals Return Name = other.Name AndAlso Address = other.Address End Function Public Overrides Function Equals(ByVal obj As Object) As Boolean If ReferenceEquals(Me, obj) Then Return True If TypeOf obj Is Contact Then Return Equals(DirectCast(obj, Contact)) Else Return False End If End Function Public Overrides Function GetHashCode() As Integer Return Name.GetHashCode Xor Address.GetHashCode End Function End Class End Module

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  • what idea is behind Zend Framework Frontcontroller/dispatcher

    - by simple
    Zend Framework FrontController implements Singleton and plus it has some kind a plugin "paradigm" , - what is the idea behind its architecture , maybe it implements some well known paradigm ? and if so then if u could give some links directions where I can find information about reasons that brought up that particular paradigm ?

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  • .NET: Interface Problem VB.net Getter Only Interface

    - by snmcdonald
    Why does an interface override a class definition and violate class encapsulation? I have included two samples below, one in C# and one in VB.net? VB.net Module Module1 Sub Main() Dim testInterface As ITest = New TestMe Console.WriteLine(testInterface.Testable) ''// Prints False testInterface.Testable = True ''// Access to Private!!! Console.WriteLine(testInterface.Testable) ''// Prints True Dim testClass As TestMe = New TestMe Console.WriteLine(testClass.Testable) ''// Prints False ''//testClass.Testable = True ''// Compile Error Console.WriteLine(testClass.Testable) ''// Prints False End Sub End Module Public Class TestMe : Implements ITest Private m_testable As Boolean = False Public Property Testable As Boolean Implements ITest.Testable Get Return m_testable End Get Private Set(ByVal value As Boolean) m_testable = value End Set End Property End Class Interface ITest Property Testable As Boolean End Interface C# using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace InterfaceCSTest { class Program { static void Main(string[] args) { ITest testInterface = new TestMe(); Console.WriteLine(testInterface.Testable); testInterface.Testable = true; Console.WriteLine(testInterface.Testable); TestMe testClass = new TestMe(); Console.WriteLine(testClass.Testable); //testClass.Testable = true; Console.WriteLine(testClass.Testable); } } class TestMe : ITest { private bool m_testable = false; public bool Testable { get { return m_testable; } private set { m_testable = value; } } } interface ITest { bool Testable { get; set; } } } More Specifically How do I implement a interface in VB.net that will allow for a private setter. For example in C# I can declare: class TestMe : ITest { private bool m_testable = false; public bool Testable { get { return m_testable; } private set //No Compile Error here! { m_testable = value; } } } interface ITest { bool Testable { get; } } However, if I declare an interface property as readonly in VB.net I cannot create a setter. If I create a VB.net interface as just a plain old property then interface declarations will violate my encapsulation. Public Class TestMe : Implements ITest Private m_testable As Boolean = False Public ReadOnly Property Testable As Boolean Implements ITest.Testable Get Return m_testable End Get Private Set(ByVal value As Boolean) ''//Compile Error m_testable = value End Set End Property End Class Interface ITest ReadOnly Property Testable As Boolean End Interface So my question is, how do I define a getter only Interface in VB.net with proper encapsulation? I figured the first example would have been the best method. However, it appears as if interface definitions overrule class definitions. So I tried to create a getter only (Readonly) property like in C# but it does not work for VB.net. Maybe this is just a limitation of the language?

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  • Dependency injection: Scoping by region (Guice, Spring, Whatever)

    - by Itay
    Here's a simplified version of my needs. I have a program where every B object has its own C and D object, injected through Guice. In addition an A object is injected into every C and D objects. What I want: that for each B object, its C and D objects will be injected with the same A object. Specifically, I want the output of the program (below) to be: Created C0 with [A0] Created D0 with [A0] Created B0 with [C0, D0] Created C1 with [A1] Created D1 with [A1] Created B1 with [C1, D1] Where it currently produces the following output: Created C0 with [A0] Created D0 with [A1] <-- Should be A0 Created B0 with [C0, D0] Created C1 with [A2] <-- Should be A1 Created D1 with [A3] <-- Should be A1 Created B1 with [C1, D1] I am expecting DI containers to allow this kind of customization but so far I had no luck in finding a solution. Below is my Guice-based code, but a Spring-based (or other DI containers-based) solution is welcome. import java.util.Arrays; import com.google.inject.*; public class Main { public static class Super { private static Map<Class<?>,Integer> map = new HashMap<Class<?>,Integer>(); private Integer value; public Super(Object... args) { value = map.get(getClass()); value = value == null ? 0 : ++value; map.put(getClass(), value); if(args.length > 0) System.out.println("Created " + this + " with " + Arrays.toString(args)); } @Override public final String toString() { return "" + getClass().getSimpleName().charAt(0) + value; } } public interface A { } public static class AImpl extends Super implements A { } public interface B { } public static class BImpl extends Super implements B { @Inject public BImpl(C c, D d) { super(c,d); } } public interface C { } public static class CImpl extends Super implements C { @Inject public CImpl(A a) { super(a); } } public interface D { } public static class DImpl extends Super implements D { @Inject public DImpl(A a) { super(a); } } public static class MyModule extends AbstractModule { @Override protected void configure() { bind(A.class).to(AImpl.class); bind(B.class).to(BImpl.class); bind(C.class).to(CImpl.class); bind(D.class).to(DImpl.class); } } public static void main(String[] args) { Injector inj = Guice.createInjector(new MyModule()); inj.getInstance(B.class); inj.getInstance(B.class); } }

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  • JPA Inheritance and Relations - Clarification question

    - by Michael
    Here the scenario: I have a unidirectional 1:N Relation from Person Entity to Address Entity. And a bidirectional 1:N Relation from User Entity to Vehicle Entity. Here is the Address class: @Entity public class Address implements Serializable { private static final long serialVersionUID = 1L; @Id @GeneratedValue(strategy = GenerationType.AUTO) privat Long int ... The Vehicles Class: @Entity public class Vehicle implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; @ManyToOne private User owner; ... @PreRemove protected void preRemove() { //this.owner.removeVehicle(this); } public Vehicle(User owner) { this.owner = owner; ... The Person Class: @Entity @Inheritance(strategy = InheritanceType.JOINED) @DiscriminatorColumn(name="PERSON_TYP") public class Person implements Serializable { @Id protected String username; @OneToMany(cascade = CascadeType.ALL, orphanRemoval=true) @JoinTable(name = "USER_ADDRESS", joinColumns = @JoinColumn(name = "USERNAME"), inverseJoinColumns = @JoinColumn(name = "ADDRESS_ID")) protected List<Address> addresses; ... @PreRemove protected void prePersonRemove(){ this.addresses = null; } ... The User Class which is inherited from the Person class: @Entity @Table(name = "Users") @DiscriminatorValue("USER") public class User extends Person { @OneToMany(mappedBy = "owner", cascade = {CascadeType.PERSIST, CascadeType.REMOVE}) private List<Vehicle> vehicles; ... When I try to delete a User who has an address I have to use orphanremoval=true on the corresponding relation (see above) and the preRemove function where the address List is set to null. Otherwise (no orphanremoval and adress list not set to null) a foreign key contraint fails. When i try to delete a user who has an vehicle a concurrent Acces Exception is thrown when do not uncomment the "this.owner.removeVehicle(this);" in the preRemove Function of the vehicle. The thing i do not understand is that before i used this inheritance there was only a User class which had all relations: @Entity @Table(name = "Users") public class User implements Serializable { @Id protected String username; @OneToMany(mappedBy = "owner", cascade = {CascadeType.PERSIST, CascadeType.REMOVE}) private List<Vehicle> vehicles; @OneToMany(cascade = CascadeType.ALL) @JoinTable(name = "USER_ADDRESS", joinColumns = @JoinColumn(name = "USERNAME") inverseJoinColumns = @JoinColumn(name = "ADDRESS_ID")) ptivate List<Address> addresses; ... No orphanremoval, and the vehicle class has used the uncommented statement above in its preRemove function. And - I could delte a user who has an address and i could delte a user who has a vehicle. So why doesn't everything work without changes when i use inheritance? I use JPA 2.0, EclipseLink 2.0.2, MySQL 5.1.x and Netbeans 6.8

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  • Textbox LostFocus event fires after Command Button's OnClick event

    - by Homam
    Hi all, I have a TextBox and a ToolStripButton in a windows forms application, the TextBox implements an event handler for the LostFocus event, and the ToolStripButton implements an event handler for the Click event, but the TextBox LostFocus event fires after the ToolStripButton Click event, which event in TextBox fires before ToolStripButton click event ?

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  • socket problem in java

    - by stefan89
    I have two classes X and Y, like this: class X implements Serializable { int val1; Y val2; } class Y implements Serializable { int val; } I want to transmit an object of type X from a client to server but i can't because the class X has a field of type Y. I replace the field of type Y with a field of type X in class X and it works.

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  • GWT - Reusing Callback Class

    - by moorsu
    My custom callback class implements AsyncCallback (like MyAsyncCallback implements AsyncCallback) and planning use single instance of MyAsyncCallback for multiple rpc method executions. Is this approach safe?. Or should have to create new instance of MyAsyncCallback for every interaction from browser to server?. I am kind of tired of seeing so many anonymous AsyncCallback code blocks. Thanks for your input

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  • C++Template in Java?

    - by RnMss
    I want something like this: public abstract class ListenerEx<LISTENER, PARENT> implements LISTENER { PARENT parent; public ListenerEx(PARENT p) { parent = p; } } But it doesn't compile. Is there a better solution? Is there something in Java like C++ template that would do check syntax after template deduction? The following explains why I need such a ListenerEX class, if you already know what it is, you don't need to read the following. I have a main window, and a button on it, and I want to get access to some method of the main window's within the listener: public class MainWindow extends JFrame { public void doSomething() { /* ... */ } public void doSomethingElse() { /* ... */ } private JButton button; public MainWindow() { button = new JButton(...); add(button); button.setActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { doSomething(); doSomethingElse(); } }); } } This would compile but does not work properly all the time. (Why would it compile when the ActionListener does not have doSomething() method?) Of course we can do it like this: public class MainWindow extends JFrame { public void doSomething() { } public void doSomethingElse() { } private JButton button; public MainWindow() { button = new JButton(...); add(button); class ActionListener1 implements ActionListener { MainWindow parent; public ActionListener(MainWindow p) { parent = p; } public void actionPerformed(ActionEvent e) { parent.doSomething(); parent.doSomethingElse(); } } button.setActionListener(new ActionListener1(this)); } } However I hate this style ... So I tried: public abstract class ActionListenerEx<P> implements ActionListener { P parent; public ActionListenerEx(P p) { parent = p; } } public class MainWindow extends JFrame { public void doSomething() { } public void doSomethingElse() { } private JButton button; public MainWindow() { button = new JButton(...); add(button); button.setActionListener(new ActionListenerEx<MainWindow>(this) { public void actionPerformed(ActionEvent e) { parent.doSomething(); parent.doSomethingElse(); } }); } } But there's lots of Listeners beside the ActionListener ... public abstract class ActionListenerEx<LISTENER, PARENT> implements LISTENER { PARENT parent; public ActionListenerEx(PARENT p) { parent = p; } } However, it won't compile ... I am fresh at Java, and I wonder if there's already better solution.

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  • Java compiler rejects variable declaration with parameterized inner class

    - by Johansensen
    I have some Groovy code which works fine in the Groovy bytecode compiler, but the Java stub generated by it causes an error in the Java compiler. I think this is probably yet another bug in the Groovy stub generator, but I really can't figure out why the Java compiler doesn't like the generated code. Here's a truncated version of the generated Java class (please excuse the ugly formatting): @groovy.util.logging.Log4j() public abstract class AbstractProcessingQueue <T> extends nz.ac.auckland.digitizer.AbstractAgent implements groovy.lang.GroovyObject { protected int retryFrequency; protected java.util.Queue<nz.ac.auckland.digitizer.AbstractProcessingQueue.ProcessingQueueMember<T>> items; public AbstractProcessingQueue (int processFrequency, int timeout, int retryFrequency) { super ((int)0, (int)0); } private enum ProcessState implements groovy.lang.GroovyObject { NEW, FAILED, FINISHED; } private class ProcessingQueueMember<E> extends java.lang.Object implements groovy.lang.GroovyObject { public ProcessingQueueMember (E object) {} } } The offending line in the generated code is this: protected java.util.Queue<nz.ac.auckland.digitizer.AbstractProcessingQueue.ProcessingQueueMember<T>> items; which produces the following compile error: [ERROR] C:\Documents and Settings\Administrator\digitizer\target\generated-sources\groovy-stubs\main\nz\ac\auckland\digitizer\AbstractProcessingQueue.java:[14,96] error: improperly formed type, type arguments given on a raw type The column index of 96 in the compile error points to the <T> parameterization of the ProcessingQueueMember type. But ProcessingQueueMember is not a raw type as the compiler claims, it is a generic type: private class ProcessingQueueMember <E> extends java.lang.Object implements groovy.lang.GroovyObject { ... I am very confused as to why the compiler thinks that the type Queue<ProcessingQueueMember<T>> is invalid. The Groovy source compiles fine, and the generated Java code looks perfectly correct to me too. What am I missing here? Is it something to do with the fact that the type in question is a nested class? (in case anyone is interested, I have filed this bug report relating to the issue in this question) Edit: Turns out this was indeed a stub compiler bug- this issue is now fixed in 1.8.9, 2.0.4 and 2.1, so if you're still having this issue just upgrade to one of those versions. :)

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  • Java serialization problem

    - by stefan89
    I have two classes X and Y, like this: class X implements Serializable { int val1; Y val2; } class Y implements Serializable { int val; } I want to transmit an object of type X from a client to server but i can't because the class X has a field of type Y. I replaced the field of type Y with a field of type X in class X and it works.

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  • Question on jpa joined table inheritance

    - by soontobeared
    Hi, The 'DiscriminatorColumn' annotation isn't creating any column in my parent entity. Where am I going wrong ? Here's my code @Entity @Inheritance(strategy=InheritanceType.JOINED) @DiscriminatorColumn(name="TYPE", discriminatorType=DiscriminatorType.STRING,length=20) public class WorkUnit extends BaseEntityClass implements Serializable{ @Entity @DiscriminatorValue(value="G") @Table(name="Group_") @PrimaryKeyJoinColumn public class Group extends WorkUnit implements Serializable{

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  • Error exposing event througt interface

    - by carlos
    I have this interface Interface IProDataSource Delegate Sub DstartingHandler(ByVal sender As Object, ByVal e As EventArgs) Event starting_Sinc As DstartingHandler End Interface Trying to use the intarce like this Public Class DataSource : Implements IProDataSource Public Event starting_Sinc As DstartingHandler Implements IProDataSource.starting_Sinc Public Delegate Sub DstartingHandler(ByVal sender As Object, ByVal e As EventArgs) End Class Gives me the next error Event 'starting_Sinc' cannot implement event 'starting_Sinc' on interface 'IProDataSource' because their delegate types 'DstartingHandler' and 'IProDataSource.DstartingHandler' do not match.

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  • How do I read and write to a file using threads in java?

    - by WarmWaffles
    I'm writing an application where I need to read blocks in from a single file, each block is roughly 512 bytes. I am also needing to write blocks simultaneously. One of the ideas I had was BlockReader implements Runnable and BlockWriter implements Runnable and BlockManager manages both the reader and writer. The problem that I am seeing with most examples that I have found was locking problems and potential deadlock situations. Any ideas how to implement this?

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  • how use in it in main project?

    - by davit-datuashvili
    I have the following interface: public interface MyFunctor { int myFunction(int x); } And I created a class which implements this interface : public class Myfunction1 implements MyFunctor { } how use in main project? i have corrected mistake now i need how run it in main project? i mean in public static void main(String[]args)?

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