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  • How do I manipulate a tree of immutable objects?

    - by Frederik
    I'm building an entire application out of immutable objects so that multi-threading and undo become easier to implement. I'm using the Google Collections Library which provides immutable versions of Map, List, and Set. My application model looks like a tree: Scene is a top-level object that contains a reference to a root Node. Each Node can contain child Nodes and Ports. An object graph might look like this: Scene | +-- Node | +-- Node | +- Port +-- Node | +- Port +- Port If all of these objects are immutable, controlled by a top-level SceneController object: What is the best way to construct this hierarchy? How would I replace an object that is arbitrarily deep in the object tree? Is there a way to support back-links, e.g. a Node having a "parent" attribute?

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  • Could someone help me debug my app (not very big)?

    - by Alex
    Not sure if this kind of help is accepted to ask for here, tell me if it isn't. It has to get done before tomorrow, it's not entirerly finished but it should work somewhat ok by now. I'm trying to use the Eclipse debugger (not very used to it). I have my top-level or main class, which is Game, in which I have a constructor and a main method. In the main method I create a new "Game", initiating the constructor. public static void main(String[] args){ Game chess = new Game(); } public Game(){ Board board = new Board(); That's the first thing the debugger reacts to: Thread [main] (Suspended) ClassNotFoundException(Object).<init>() line: 20 [local variables unavailable] ClassNotFoundException(Throwable).<init>(String, Throwable) line: 217 ClassNotFoundException(Exception).<init>(String, Throwable) line: not available ClassNotFoundException.<init>(String) line: not available URLClassLoader$1.run() line: not available AccessController.doPrivileged(PrivilegedExceptionAction<T>, AccessControlContext) line: not available [native method] Launcher$ExtClassLoader(URLClassLoader).findClass(String) line: not available Launcher$ExtClassLoader.findClass(String) line: not available Launcher$ExtClassLoader(ClassLoader).loadClass(String, boolean) line: not available Launcher$AppClassLoader(ClassLoader).loadClass(String, boolean) line: not available Launcher$AppClassLoader.loadClass(String, boolean) line: not available Launcher$AppClassLoader(ClassLoader).loadClass(String) line: not available Game.<init>() line: 15 Game.main(String[]) line: 11 Line 11 is the one line in my main method, line 15 is the instantiation of "board".

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  • Hibernate - Persisting polymorphic joins

    - by Marty Pitt
    Hi I'm trying to understand how to best implement a polymorphic one-to-many in hibernate. Eg: @MappedSuperclass public class BaseEntity { Integer id; // etc... } @Entity public class Author extends BaseEntity {} @Entity public class Post extends BaseEntity {} @Entity public class Comment extends BaseEntity {} And now, I'd like to also persist audit information, with the following class: @Entity public class AuditEvent { @ManyToOne // ? BaseEntity entity; } What is the appropriate mapping for auditEvent.entity? Also, how will Hibernate actually persist this? Would a series of join tables be generated (AuditEvent_Author , AuditEvent_Post, AuditEvent_Comment), or is there a better way? Note, I'd rather not have my other entity classes expose the other side of the join (eg., List<AuditEvent> events on BaseEntity) - but if that's the cleanest way to implement, then it will suffice.

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  • How to change the way that timer schedules in TimerTask?

    - by Judking
    Here is the code snippet: Timer t = new Timer(); TimerTask task = new TimerTask() { @Override public void run() { //change the timer rate of scheduleAtFixedRate here } }; //every 10 sec t.scheduleAtFixedRate(task, new Date(), 10000); Could anyone tell me how to change the rate of timer to t.scheduleAtFixedRate(task, new Date(), 30000) in method run from TimerTask instance? Thanks a lot!

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  • proper way to use list to array?

    - by cometta
    public class TestClass{ private String divisions[] ={}; public void doAction(){ Collection testArray = new ArrayList(); // put testArray will data divisions = (String [] ) testArray.toArray(division); //should i use this divisions = (String [] ) testArray.toArray(new String [] {}); //should i use this? } } if i use case 1, and i call doaction multiple time, the division, something will show wrong records if i use case2, divisions will always show the correct records. is my assumption should use case 2?

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  • How to properly mix generics and inheritance to get the desired result?

    - by yamsha
    My question is not easy to explain using words, fortunately it's not too difficult to demonstrate. So, bear with me: public interface Command<R> { public R execute();//parameter R is the type of object that will be returned as the result of the execution of this command } public abstract class BasicCommand<R> { } public interface CommandProcessor<C extends Command<?>> { public <R> R process(C<R> command);//this is my question... it's illegal to do, but you understand the idea behind it, right? } //constrain BasicCommandProcessor to commands that subclass BasicCommand public class BasicCommandProcessor implements CommandProcessor<C extends BasicCommand<?>> { //here, only subclasses of BasicCommand should be allowed as arguments but these //BasicCommand object should be parameterized by R, like so: BasicCommand<R> //so the method signature should really be // public <R> R process(BasicCommand<R> command) //which would break the inheritance if the interface's method signature was instead: // public <R> R process(Command<R> command); //I really hope this fully illustrates my conundrum public <R> R process(C<R> command) { return command.execute(); } } public class CommandContext { public static void main(String... args) { BasicCommandProcessor bcp = new BasicCommandProcessor(); String textResult = bcp.execute(new BasicCommand<String>() { public String execute() { return "result"; } }); Long numericResult = bcp.execute(new BasicCommand<Long>() { public Long execute() { return 123L; } }); } } Basically, I want the generic "process" method to dictate the type of generic parameter of the Command object. The goal is to be able to restrict different implementations of CommandProcessor to certain classes that implement Command interface and at the same time to able to call the process method of any class that implements the CommandProcessor interface and have it return the object of type specified by the parametarized Command object. I'm not sure if my explanation is clear enough, so please let me know if further explanation is needed. I guess, the question is "Would this be possible to do, at all?" If the answer is "No" what would be the best work-around (I thought of a couple on my own, but I'd like some fresh ideas)

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  • Is this technically thread safe despite being mutable?

    - by Finbarr
    Yes, the private member variable bar should be final right? But actually, in this instance, it is an atomic operation to simply read the value of an int. So is this technically thread safe? class foo { private int bar; public foo(int bar) { this.bar = bar; } public int getBar() { return bar; } } // assume infinite number of threads repeatedly calling getBar on the same instance of foo.

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  • Clone a 'link' in SWT

    - by Steve
    I have a table of information that includes a username, an ip address, and a timestamp. What I wanted to do was to have the ip address contained within a link object that when the link is clicked it utilizes bgp.he.net to get information about the host/IP address. I have tried creating threads to resolve the IP addresses but it is often a large amount of IP addresses and I read that InetAddress#getByName isn't non-blocking, so I figured having links that go to this site is the next best thing. Question is: Is it possible to have links for each of my IP addresses in the table without creating a new link object for each row? I don't know how bad that would be on memory usage which is why I'm inquiring about cloning an instance of an IP and having the link open bgp.he.net/link.getText()

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  • Figuring out QuadCurveTo's parameters

    - by Fev
    Could you guys help me figuring out QuadCurveTo's 4 parameters , I tried to find information on http://docs.oracle.com/javafx/2/api/javafx/scene/shape/QuadCurveTo.html, but it's hard for me to understand without picture , I search on google about 'Quadratic Bezier' but it shows me more than 2 coordinates, I'm confused and blind now. I know those 4 parameters draw 2 lines to control the path , but how we know/count exactly which coordinates the object will throught by only knowing those 2 path-controller. Are there some formulas? import javafx.animation.PathTransition; import javafx.animation.PathTransition.OrientationType; import javafx.application.Application; import static javafx.application.Application.launch; import javafx.scene.Group; import javafx.scene.Scene; import javafx.scene.paint.Color; import javafx.scene.shape.MoveTo; import javafx.scene.shape.Path; import javafx.scene.shape.QuadCurveTo; import javafx.scene.shape.Rectangle; import javafx.stage.Stage; import javafx.util.Duration; public class _6 extends Application { public Rectangle r; @Override public void start(final Stage stage) { r = new Rectangle(50, 80, 80, 90); r.setFill(javafx.scene.paint.Color.ORANGE); r.setStrokeWidth(5); r.setStroke(Color.ANTIQUEWHITE); Path path = new Path(); path.getElements().add(new MoveTo(100.0f, 400.0f)); path.getElements().add(new QuadCurveTo(150.0f, 60.0f, 100.0f, 20.0f)); PathTransition pt = new PathTransition(Duration.millis(1000), path); pt.setDuration(Duration.millis(10000)); pt.setNode(r); pt.setPath(path); pt.setOrientation(OrientationType.ORTHOGONAL_TO_TANGENT); pt.setCycleCount(4000); pt.setAutoReverse(true); pt.play(); stage.setScene(new Scene(new Group(r), 500, 700)); stage.show(); } public static void main(String[] args) { launch(args); } } You can find those coordinates on this new QuadCurveTo(150.0f, 60.0f, 100.0f, 20.0f) line, and below is the picture of Quadratic Bezier

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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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  • Joining tables with composite keys in a legacy system in hibernate

    - by Steve N
    Hi, I'm currently trying to create a pair of Hibernate annotated classes to load (read only) from a pair of tables in a legacy system. The legacy system uses a consistent (if somewhat dated) approach to keying tables. The tables I'm attempting to map are as follows: Customer CustomerAddress -------------------------- ---------------------------- customerNumber:string (pk) customerNumber:string (pk_1) name:string sequenceNumber:int (pk_2) street:string postalCode:string I've approached this by creating a CustomerAddress class like this: @Entity @Table(name="CustomerAddress") @IdClass(CustomerAddressKey.class) public class CustomerAddress { @Id @AttributeOverrides({ @AttributeOverride(name = "customerNumber", column = @Column(name="customerNumber")), @AttributeOverride(name = "sequenceNumber", column = @Column(name="sequenceNumber")) }) private String customerNumber; private int sequenceNumber; private String name; private String postalCode; ... } Where the CustomerAddressKey class is a simple Serializable object with the two key fields. The Customer object is then defined as: @Entity @Table(name = "Customer") public class Customer { private String customerNumber; private List<CustomerAddress> addresses = new ArrayList<CustomerAddress>(); private String name; ... } So, my question is: how do I express the OneToMany relationship on the Customer table?

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  • Can I replicate some of the optimisations done by the JVM by hand?

    - by Subb
    I'm working on a Sudoku solver at school and we're having a little performance contest. Right now, my algorithm is pretty fast on the first run (about 2.5ms), but even faster when I solve the same puzzle 10 000 times (about 0.5ms for each run). Those timing are, of course, depend of the puzzle being solved. I know the JVM do some optimization when a method is called multiple time, and this is what I suspect is happening. I don't think I can further optimize the algorithm itself (though I'll keep looking), so I was wondering if I could replicate some of the optimizations done by the JVM. Note : compiling to native code is not an option Thanks!

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  • Unit testing nested subflows (subflows of subflows)

    - by snusmumrik
    I'm trying to write unit test for a flow, which has subflow, which, itself, has another subflow. I register first flow using FlowDefinitionResource getResource(FlowDefinitionResourceFactory resourceFactory). Then I register subflow definitions during test execution in FlowDefinitionRegistry before transitioning to them. Transitioning to "first level" subflow goes ok. The result of transitioning to subflow of current subflow - NoSuchFlowDefinitionException. The problem is that subflow definitions are all seem attached to the primary flow of the test and subflow can't be found within another subflow. Is there any way to attach subflow definition to another subflow in tests, which extend AbstractXmlFlowExecutionTests?

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  • How to get the type of the class for comparison

    - by Halo
    I have this object which is an instance of a superclass. I want to know which subclass that object really is, so that I can decide what to do with it. There is this getClass() method but it's apparently not used for comparison issues. How can I get the sub-type of my object?

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  • Can I include both Apache Axis 1 and 2 libraries in the same project?

    - by ian_scho_es
    If it sounds like a ridiculous idea then it is. The client only wants to have to install one project on their server. Our web service will be bridging between mobile phones and various SOAP services made in .NET, Apache Axis 1 and 2, which rely on standards to transfer files such as MTOM and DIME. I am looking for an 'architecture' trick, such as develop the Axis 1 calls in a separate project and compile as a jar, to then pass it into the Axis 2 project.... Hmmm. Anything rather than having to download the source code for Axis 1 & 2 and compile them using the same xml libraries, etc. "It can't be done" is an acceptable answer. Thanks!

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  • String Object. Clarification needed

    - by mac
    Guys, help me clarify. Say i have the following line in my program: jobSetupErrors.append("abc"); In the case above where jobSetupErrors is a StringBuilder(), what i see happen is: New String Object is created and assigned value "abc" value of that String object is assigned to the existing StringBuilder object If that is correct, and I add 1 more line ... jobSetupErrors.append("abc"); logger.info("abc"); In the above example are we creating String object separately 2 times? If so, would it be more proper to do something like this? String a = "abc"; jobSetupErrors.append(a); logger.info(a); Is this a better approach? Please advise

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  • Abstract class get parameter from implementing subclass?

    - by soren.qvist
    I'm wondering if there is way to do this without breaking encapsulation, I want the abstract class to rely on parameters defined in the implementing subclass. Like so: public abstract class Parent { private int size; private List<String> someList; public Parent() { size = getSize(); someList = new ArrayList<String>(size); } public abstract int getSize(); } public class Child extends Parent { @Override public int getSize() { return 5; } } Is this ugly? Is there a better way? And perhaps more importantly, is this even a good idea?

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  • HTML/CSS Rendering to Image

    - by Steve
    Is there a library or tool that can take an html page and some css, and then render an image? I would like to define some templates server side using html code snippets, and some CSS to define the layout. Then using the template and CSS, I would like to essentially render an image of how this would display in a browser, and pass the image back to the client. Thanks.

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