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• Why is there no service-oriented language?

  - by Wolfgang

  Edit: To avoid further confusion: I am not talking about web services and such. I am talking about structuring applications internally, it's not about how computers communicate. It's about programming languages, compilers and how the imperative programming paradigm is extended. Original: In the imperative programming field, we saw two paradigms in the past 20 years (or more): object-oriented (OO), and service-oriented (SO) aka. component-based (CB). Both paradigms extend the imperative programming paradigm by introducing their own notion of modules. OO calls them objects (and classes) and lets them encapsulates both data (fields) and procedures (methods) together. SO, in contrast, separates data (records, beans, ...) from code (components, services). However, only OO has programming languages which natively support its paradigm: Smalltalk, C++, Java and all other JVM-compatibles, C# and all other .NET-compatibles, Python etc. SO has no such native language. It only comes into existence on top of procedural languages or OO languages: COM/DCOM (binary, C, C++), CORBA, EJB, Spring, Guice (all Java), ... These SO frameworks clearly suffer from the missing native language support of their concepts. They start using OO classes to represent services and records. This leads to designs where there is a clear distinction between classes that have methods only (services) and those that have fields only (records). Inheritance between services or records is then simulated by inheritance of classes. Technically, its not kept so strictly but in general programmers are adviced to make classes to play only one of the two roles. They use additional, external languages to represent the missing parts: IDL's, XML configurations, Annotations in Java code, or even embedded DSL like in Guice. This is especially needed, but not limited to, since the composition of services is not part of the service code itself. In OO, objects create other objects so there is no need for such facilities but for SO there is because services don't instantiate or configure other services. They establish an inner-platform effect on top of OO (early EJB, CORBA) where the programmer has to write all the code that is needed to "drive" SO. Classes represent only a part of the nature of a service and lots of classes have to be written to form a service together. All that boiler plate is necessary because there is no SO compiler which would do it for the programmer. This is just like some people did it in C for OO when there was no C++. You just pass the record which holds the data of the object as a first parameter to the procedure which is the method. In a OO language this parameter is implicit and the compiler produces all the code that we need for virtual functions etc. For SO, this is clearly missing. Especially the newer frameworks extensively use AOP or introspection to add the missing parts to a OO language. This doesn't bring the necessary language expressiveness but avoids the boiler platform code described in the previous point. Some frameworks use code generation to produce the boiler plate code. Configuration files in XML or annotations in OO code is the source of information for this. Not all of the phenomena that I mentioned above can be attributed to SO but I hope it clearly shows that there is a need for a SO language. Since this paradigm is so popular: why isn't there one? Or maybe there are some academic ones but at least the industry doesn't use one.

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• What are the disadvantages of self-encapsulation?

  - by Dave Jarvis

  Background Tony Hoare's billion dollar mistake was the invention of null. Subsequently, a lot of code has become riddled with null pointer exceptions (segfaults) when software developers try to use (dereference) uninitialized variables. In 1989, Wirfs-Brock and Wikerson wrote: Direct references to variables severely limit the ability of programmers to re?ne existing classes. The programming conventions described here structure the use of variables to promote reusable designs. We encourage users of all object-oriented languages to follow these conventions. Additionally, we strongly urge designers of object-oriented languages to consider the effects of unrestricted variable references on reusability. Problem A lot of software, especially in Java, but likely in C# and C++, often uses the following pattern: public class SomeClass { private String someAttribute; public SomeClass() { this.someAttribute = "Some Value"; } public void someMethod() { if( this.someAttribute.equals( "Some Value" ) ) { // do something... } } public void setAttribute( String s ) { this.someAttribute = s; } public String getAttribute() { return this.someAttribute; } } Sometimes a band-aid solution is used by checking for null throughout the code base: public void someMethod() { assert this.someAttribute != null; if( this.someAttribute.equals( "Some Value" ) ) { // do something... } } public void anotherMethod() { assert this.someAttribute != null; if( this.someAttribute.equals( "Some Default Value" ) ) { // do something... } } The band-aid does not always avoid the null pointer problem: a race condition exists. The race condition is mitigated using: public void anotherMethod() { String someAttribute = this.someAttribute; assert someAttribute != null; if( someAttribute.equals( "Some Default Value" ) ) { // do something... } } Yet that requires two statements (assignment to local copy and check for null) every time a class-scoped variable is used to ensure it is valid. Self-Encapsulation Ken Auer's Reusability Through Self-Encapsulation (Pattern Languages of Program Design, Addison Wesley, New York, pp. 505-516, 1994) advocated self-encapsulation combined with lazy initialization. The result, in Java, would resemble: public class SomeClass { private String someAttribute; public SomeClass() { setAttribute( "Some Value" ); } public void someMethod() { if( getAttribute().equals( "Some Value" ) ) { // do something... } } public void setAttribute( String s ) { this.someAttribute = s; } public String getAttribute() { String someAttribute = this.someAttribute; if( someAttribute == null ) { setAttribute( createDefaultValue() ); } return someAttribute; } protected String createDefaultValue() { return "Some Default Value"; } } All duplicate checks for null are superfluous: getAttribute() ensures the value is never null at a single location within the containing class. Efficiency arguments should be fairly moot -- modern compilers and virtual machines can inline the code when possible. As long as variables are never referenced directly, this also allows for proper application of the Open-Closed Principle. Question What are the disadvantages of self-encapsulation, if any? (Ideally, I would like to see references to studies that contrast the robustness of similarly complex systems that use and don't use self-encapsulation, as this strikes me as a fairly straightforward testable hypothesis.)

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• Is my class structure good enough?

  - by Rivten

  So I wanted to try out this challenge on reddit which is mostly about how you structure your data the best you can. I decided to challenge my C++ skills. Here's how I planned this. First, there's the Game class. It deals with time and is the only class main has access to. A game has a Forest. For now, this class does not have a lot of things, only a size and a Factory. Will be put in better use when it will come to SDL-stuff I guess A Factory is the thing that deals with the Game Objects (a.k.a. Trees, Lumberjack and Bears). It has a vector of all GameObjects and a queue of Events which will be managed at the end of one month. A GameObject is an abstract class which can be updated and which can notify the Event Listener The EventListener is a class which handles all the Events of a simulation. It can recieve events from a Game Object and notify the Factory if needed, the latter will manage correctly the event. So, the Tree, Lumberjack and Bear classes all inherits from GameObject. And Sapling and Elder Tree inherits from Tree. Finally, an Event is defined by an event_type enumeration (LUMBERJACK_MAWED, SAPPLING_EVOLUTION, ...) and an event_protagonists union (a GameObject or a pair of GameObject (who killed who ?)). I was quite happy at first with this because it seems quite logic and flexible. But I ended up questionning this structure. Here's why : I dislike the fact that a GameObject need to know about the Factory. Indeed, when a Bear moves somewhere, it needs to know if there's a Lumberjack ! Or it is the Factory which handles places and objects. It would be great if a GameObject could only interact with the EventListener... or maybe it's not that much of a big deal. Wouldn't it be better if I separate the Factory in three vectors ? One for each kind of GameObject. The idea would be to optimize research. If I'm looking do delete a dead lumberjack, I would only have to look in one shorter vector rather than a very long vector. Another problem arises when I want to know if there is any particular object in a given case because I have to look for all the gameObjects and see if they are at the given case. I would tend to think that the other idea would be to use a matrix but then the issue would be that I would have empty cases (and therefore unused space). I don't really know if Sapling and Elder Tree should inherit from Tree. Indeed, a Sapling is a Tree but what about its evolution ? Should I just delete the sapling and say to the factory to create a new Tree at the exact same place ? It doesn't seem natural to me to do so. How could I improve this ? Is the design of an Event quite good ? I've never used unions before in C++ but I didn't have any other ideas about what to use. Well, I hope I have been clear enough. Thank you for taking the time to help me !

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• Can I set a property on an object that is only declared on the instance type, when I don't know the

  - by WilberBeast

  Let me explain. I have a List into which I am adding various ASP.NET controls. I then wish to loop through the list and set a CssClass, however not every Control supports the property CssClass. What I would like to do is test if the underlying instance type supports the CssClass property and set it, but I'm not sure how to do the conversion prior to setting the property since I don't know the type of each Control object. I know that I can use typeof or x.GetType(), but I'm not sure how to use these to convert the controls back to the instance type in order to test for and then set the property. Actually I seem to have solved this, so I thought that I would post the code here for others. foreach (Control c in controlList) { PropertyInfo pi = c.GetType().GetProperty("CssClass"); if (pi != null) pi.SetValue(c, "desired_css_class", null); } I hope that this helps someone else as I has taken me hours to research these 2 lines of code. Cheers Steve

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• Why ruby object has two to_s and inspect methods that (looks like) do the same thing?

  - by prosseek

  The p calls inspect, and puts/print calls to_s for representing its object. If I run class Graph def initialize @nodeArray = Array.new @wireArray = Array.new end def to_s # called with print / puts "Graph : #{@nodeArray.size}" end def inspect # called with p "G" end end if __FILE__ == $0 gr = Graph.new p gr print gr puts gr end I get G Graph : 0Graph : 0 Then, why does ruby has two functions do the same thing? What makes the difference between to_s and inspect? And what's the difference between puts/print/p? If I comment out the to_s or inspect function, I get as follows. #<Graph:0x100124b88>#<Graph:0x100124b88>

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• Java: How do you access a sub-object of an object with no "getXXX" method to that sub-object

  - by Daxon

  I'll explain with pictures from Eclipse Debugger I have an Class called "FieldContext", (I can't edit it, it's compiled in the Java OVal API) Within "FieldContext" on the eclipse variable tab are "CompileTimeType" and "field" Q1 Is there a legend for the icons in the variables tab? like what the red box with the "F" means + yellow diamond boxes? Now I want to access the fields inside the "field" object (RedBox) .. preferably "name" But the "FieldContext" does not have a "getField()" method, yet it has a "getCompileTimeType()" method. Q2 So is there anyway to get that field object being a "SerializableField" Class from the "FieldContext"? If eclipse debugger can see/get/edit them then I hope I can do the same in Java.

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• How to get elements from an object in C#?

  - by Drew

  I am using the AutoCompleteBox in WPF, I populate the suggestions with a List that consists of four fields. When the user selects an item and I reach my eventHandler, i can see that MyAutoCompleteBox.SelectedItem is an object that has my four values, if i hover this text in the debugger i can see the four values listed, however i don't know how to access these values in the code. I tried List<Codes> selected = MyAutoCompleteBox.SelectedItem as List<Codes>; where Codes is my List. selected returns as null and empty every time. Is there a way to get to these values? Thanks!

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• How should I implement items that are normalized in the Database, in Object Oriented Design?

  - by Jonas

  How should I implement items that are normalized in the Database, in Object Oriented classes? In the database I have a big table of items and a smaller of groups. Each item belong to one group. This is how my database design look like: +----------------------------------------+ | Inventory | +----+------+-------+----------+---------+ | Id | Name | Price | Quantity | GroupId | +----+------+-------+----------+---------+ | 43 | Box | 34.00 | 456 | 4 | | 56 | Ball | 56.50 | 3 | 6 | | 66 | Tin | 23.00 | 14 | 4 | +----+------+-------+----------+---------+ Totally 3000 lines +----------------------+ | Groups | +---------+------+-----+ | GroupId | Name | VAT | +---------+------+-----+ | 4 | Mini | 0.2 | | 6 | Big | 0.3 | +---------+------+-----+ Totally 10 lines I will use the OOP classes in a GUI, where the user can edit Items and Groups in the inventory. It should also be easy to do calculations with a bunch of items. The group information like VAT are needed for the calculations. I will write an Item class, but do I need a Group class? and if I need it, should I keep them in a global location or how do I access it when I need it for Item-calculations? Is there any design pattern for this case?

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• What's The Best Object-Relational Mapping Tool For .NET?

  - by Icono123

  I've worked on a few Java web projects and we've always used Hibernate for our data object layer. I haven't worked on a large scale ASP.NET site and I'm unsure which solution to choose. I'm tempted to try NHibernate, but I don't like the fact that they use so many third party libraries. I found this list on Wikipedia of available ORM software: http://en.wikipedia.org/wiki/List_of_object-relational_mapping_software#.NET What ORM have you used? Was it easy to use? Would you recommend using it again? Was it used on a small, medium, or large project? Would you write your own? Thanks.

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• What could possibly cause this error when declaring an object inside a class?

  - by M4design

  I'm battling with this assignment :) I've got two classes: Ocean and Grid. When I declare an object of the Grid inside the Ocean: unsigned int sharkCount; Grid grid; The compiler/complainer says: error C2146: syntax error : missing ';' before identifier 'grid' Can you possibly predict what produces this error with the limited info I provided? It seems that as if the Ocean doesn't like the Grid class. Could this be because of the poor implementation of the grid class. BTW the Grid has a default constructor. Yet the error happens in compiling time!. EDIT: They're each in separate header file, and I've included the Grid.h in the Ocean.h.

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• How can I access this nested array within my JSON object?

  - by Charles

  I'm using PHP to return a json_encode()'d array for use in my Javascript code. It's being returned as: {"parent1[]":["child1","child2","child2"],"parent2[]":["child1"]} By using the following code, I am able to access parent2 > child1 $.getJSON('myfile.php', function(data) { for (var key in data) { alert(data[key]); } } However, this doesn't give me access to child1, child2, child, of parent1. Alerting the key by itself shows 'parent1' but when I try to alert it's contents, I get undefined. I figured it would give me an object/array? How do I access the children of parent1? data[key][0] ?

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• What could possibly cause this error(when declaring an object inside a class) ? //noobie question

  - by M4design

  I'm battling with this assignment :) I've got two classes: Ocean and Grid. When I declare an object of the Grid inside the Ocean: unsigned int sharkCount; Grid grid; The compiler/complainer says: error C2146: syntax error : missing ';' before identifier 'grid' Can you possibly predict what produces this error with the limited info' I provided? It seems that as if the Ocean doesn't like the Grid class. Could this be because of the poor implementation of the grid class. BTW the Grid has a default constructor. Yet the error happens in compiling time!. Thanks. EDIT: They're each in separate header file, and I've included the Grid.h in the Ocean.h.

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• TypeError: Result of expression 'printWindow' [undefined] is not an object.

  - by orangebrainer

  I'm trying to create hidden iframes in my page dynamically to load 3 other pages so that i can grab all the HTML and combine them into 1 in a new window. However i'm stuck at this. tHe frames are created fine. But whenever the javascript runs to the part of function openNewWindow() { var printWindow = window.open("",""); printWindow.document.open(); printWindow.document.write(HTMLfromFrames); printWindow.document.close(); } i get this error: TypeError: Result of expression 'printWindow' [undefined] is not an object. but if i generate a button to call this function seperately, it works fine. however i need it to run all in one click event Anybody has any idea what's wrong? Thanks!

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• What's wrong with the architecture of a game object drawing and updating itself?

  - by Ricket

  What are the reasons for and against a game object drawing and updating itself? For example, if you have a game where the player has a position on screen, why not have an all-encompassing class: public class Player { private int x, y, xVelocity, yVelocity; private Sprite s; //... public Player() { // load the sprite here, somehow? } public void draw(CustomGraphicsClass g) { g.draw(s, x, y); } public void update(long timeElapsed) { x += (xVelocity * timeElapsed); y += (yVelocity * timeElapsed); } } What is wrong with this design? What are the downfalls or concerns? How would you better write something like this, or better architect this type of thing in a game? Also, somewhat connected, how would you implement loading that Sprite image? And furthermore, how would you then implement collision between two Players? (I should probably separate these extra two questions into new questions, huh?)

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• ypeError: Result of expression 'printWindow' [undefined] is not an object.

  - by orangebrainer

  I'm trying to create hidden iframes in my page dynamically to load 3 other pages so that i can grab all the HTML and combine them into 1 in a new window. However i'm stuck at this. tHe frames are created fine. But whenever the javascript runs to the part of openNewWindow(); { var printWindow = window.open("",""); printWindow.document.open(); printWindow.document.write(HTMLfromFrames); printWindow.document.close(); } i get this error: TypeError: Result of expression 'printWindow' [undefined] is not an object. but if i generate a button to call this function seperately, it works fine. however i need it to run all in one click event Anybody as any idea what's wrong? Thanks!

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• Connection to Weblogic Server through ServiceMix fails

  - by bertolami

  I connect from a OSGi bundle deployed on Apache ServiceMix to a Weblogic Server to call some EJBs. The lookup happens with JNDI. In my unit test everything works fine. But when a deploy the bundle on ServiceMix a CommunicationException exception is raised on JNDI ContextFactory initialisation. The class that performs the lookup during initialisation: public DummyJndiLookup(JndiTemplate jndiTemplate) { try { String securityServiceURL = "ejb/xyz/Service"; reference = jndiTemplate.lookup(securityServiceURL); log.info("Successfully connected to JNDI Server: " + reference); } catch (Throwable t) { throw new RuntimeException(t); } } The beans in the spring context: <bean id="dummy" class="xyz.DummyJndiLookup"> <constructor-arg ref="jndiTemplate"></constructor-arg> </bean> <bean id="jndiTemplate" class="org.springframework.jndi.JndiTemplate" lazy-init="true"> <property name="environment"> <props> <prop key="java.naming.factory.initial">weblogic.jndi.WLInitialContextFactory</prop> <prop key="java.naming.provider.url">t3://xyz:22225</prop> <prop key="java.naming.security.principal">weblogic</prop> <prop key="java.naming.security.credentials">weblogic</prop> </props> </property> </bean> The resulting exception stack trace: Caused by: javax.naming.CommunicationException [Root exception is java.net.ConnectException: t3://xyz7:22225: Bootstrap to: xyz/192.168.108.22:22225' over: 't3' got an error or timed out] at weblogic.jndi.internal.ExceptionTranslator.toNamingException(ExceptionTranslator.java:40) at weblogic.jndi.WLInitialContextFactoryDelegate.toNamingException(WLInitialContextFactoryDelegate.java:783) at weblogic.jndi.WLInitialContextFactoryDelegate.getInitialContext(WLInitialContextFactoryDelegate.java:365) at weblogic.jndi.Environment.getContext(Environment.java:315) at weblogic.jndi.Environment.getContext(Environment.java:285) at weblogic.jndi.WLInitialContextFactory.getInitialContext(WLInitialContextFactory.java:117) at javax.naming.spi.NamingManager.getInitialContext(NamingManager.java:667) at javax.naming.InitialContext.getDefaultInitCtx(InitialContext.java:288) at javax.naming.InitialContext.init(InitialContext.java:223) at javax.naming.InitialContext.<init>(InitialContext.java:197) at org.springframework.jndi.JndiTemplate.createInitialContext(JndiTemplate.java:137) at org.springframework.jndi.JndiTemplate.getContext(JndiTemplate.java:104) at org.springframework.jndi.JndiTemplate.execute(JndiTemplate.java:86) at org.springframework.jndi.JndiTemplate.lookup(JndiTemplate.java:153) at xyz.DummyJndiLookup.<init>(DummyJndiLookup.java:36) ... 26 more Caused by: java.net.ConnectException: t3://xyz:22225: Bootstrap to: xyz/192.168.108.22:22225' over: 't3' got an error or timed out at weblogic.rjvm.RJVMFinder.findOrCreateInternal(RJVMFinder.java:216) at weblogic.rjvm.RJVMFinder.findOrCreate(RJVMFinder.java:170) at weblogic.rjvm.ServerURL.findOrCreateRJVM(ServerURL.java:153) at weblogic.jndi.WLInitialContextFactoryDelegate$1.run(WLInitialContextFactoryDelegate.java:344) at weblogic.security.acl.internal.AuthenticatedSubject.doAs(AuthenticatedSubject.java:363) at weblogic.security.service.SecurityManager.runAs(SecurityManager.java:147) at weblogic.jndi.WLInitialContextFactoryDelegate.getInitialContext(WLInitialContextFactoryDelegate.java:339) ... 38 more Caused by: java.rmi.ConnectException: Bootstrap to: xyz/192.168.108.22:22225' over: 't3' got an error or timed out at weblogic.rjvm.ConnectionManager.bootstrap(ConnectionManager.java:359) at weblogic.rjvm.RJVMManager.findOrCreateRemoteInternal(RJVMManager.java:251) at weblogic.rjvm.RJVMManager.findOrCreate(RJVMManager.java:194) at weblogic.rjvm.RJVMFinder.findOrCreateRemoteServer(RJVMFinder.java:238) at weblogic.rjvm.RJVMFinder.findOrCreateInternal(RJVMFinder.java:200) Any ideas what could cause the exception? Escpecially why it does work in the unit test and not after having bundled and deployed on Apache ServiceMix? Additional Info: I dumped the threads stack trace of ServiceMix (after having removed all JNDI related spring stuff): 2010-03-22 16:18:23 Full thread dump Java HotSpot(TM) Server VM (11.2-b01 mixed mode): "SpringOsgiExtenderThread-14" prio=6 tid=0x054d6400 nid=0x17c4 waiting for monitor entry [0x06f3e000..0x06f3fb14] java.lang.Thread.State: BLOCKED (on object monitor) at weblogic.rjvm.RJVMFinder.findOrCreate(RJVMFinder.java:168) - waiting to lock <0x595876f8> (a weblogic.rjvm.RJVMFinder) at weblogic.rjvm.ServerURL.findOrCreateRJVM(ServerURL.java:153) at weblogic.jndi.WLInitialContextFactoryDelegate.getInitialContext(WLInitialContextFactoryDelegate.java:352) at weblogic.jndi.Environment.getContext(Environment.java:315) at weblogic.jndi.Environment.getContext(Environment.java:285) at weblogic.jndi.WLInitialContextFactory.getInitialContext(WLInitialContextFactory.java:117) at javax.naming.spi.NamingManager.getInitialContext(NamingManager.java:667) at javax.naming.InitialContext.getDefaultInitCtx(InitialContext.java:288) at javax.naming.InitialContext.init(InitialContext.java:223) at javax.naming.InitialContext.<init>(InitialContext.java:197) at xyz.DummyJndiLookup.getInitialContext(DummyJndiLookup.java:62) at xyz.DummyJndiLookup.<init>(DummyJndiLookup.java:32) at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27) at java.lang.reflect.Constructor.newInstance(Constructor.java:513) at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:100) at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:61) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:877) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:839) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:440) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409) at java.security.AccessController.doPrivileged(Native Method) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380) at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:264) at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) - locked <0x595959c0> (a java.util.concurrent.ConcurrentHashMap) at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:261) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164) at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:429) - locked <0x59598370> (a java.util.concurrent.ConcurrentHashMap) at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:728) at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext.access$1600(AbstractDelegatedExecutionApplicationContext.java:69) at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext$4.run(AbstractDelegatedExecutionApplicationContext.java:355) - locked <0x595431a8> (a java.lang.Object) at org.springframework.osgi.util.internal.PrivilegedUtils.executeWithCustomTCCL(PrivilegedUtils.java:85) at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext.completeRefresh(AbstractDelegatedExecutionApplicationContext.java:320) at org.springframework.osgi.extender.internal.dependencies.startup.DependencyWaiterApplicationContextExecutor$CompleteRefreshTask.run(DependencyWaiterApplicationContextExecutor.java:136) at java.lang.Thread.run(Thread.java:619) Locked ownable synchronizers: - None "SpringOsgiExtenderThread-12" prio=6 tid=0x05465400 nid=0x14cc in Object.wait() [0x06f8e000..0x06f8fc94] java.lang.Thread.State: TIMED_WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x595b3800> (a java.lang.Object) at weblogic.rjvm.ConnectionManager.bootstrap(ConnectionManager.java:320) - locked <0x595b3800> (a java.lang.Object) at weblogic.rjvm.RJVMManager.findOrCreateRemoteInternal(RJVMManager.java:251) - locked <0x595885b8> (a java.lang.Object) at weblogic.rjvm.RJVMManager.findOrCreate(RJVMManager.java:194) at weblogic.rjvm.RJVMFinder.findOrCreateRemoteServer(RJVMFinder.java:238) at weblogic.rjvm.RJVMFinder.findOrCreateInternal(RJVMFinder.java:200) at weblogic.rjvm.RJVMFinder.findOrCreate(RJVMFinder.java:170) - locked <0x595876f8> (a weblogic.rjvm.RJVMFinder) at weblogic.rjvm.ServerURL.findOrCreateRJVM(ServerURL.java:153) at weblogic.jndi.WLInitialContextFactoryDelegate.getInitialContext(WLInitialContextFactoryDelegate.java:352) at weblogic.jndi.Environment.getContext(Environment.java:315) at weblogic.jndi.Environment.getContext(Environment.java:285) at weblogic.jndi.WLInitialContextFactory.getInitialContext(WLInitialContextFactory.java:117) at javax.naming.spi.NamingManager.getInitialContext(NamingManager.java:667) at javax.naming.InitialContext.getDefaultInitCtx(InitialContext.java:288) at javax.naming.InitialContext.init(InitialContext.java:223) at javax.naming.InitialContext.<init>(InitialContext.java:197) at xyz.DummyJndiLookup.getInitialContext(DummyJndiLookup.java:62) at xyz.DummyJndiLookup.<init>(DummyJndiLookup.java:32) at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27) at java.lang.reflect.Constructor.newInstance(Constructor.java:513) at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:100) at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:61) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:877) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:839) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:440) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409) at java.security.AccessController.doPrivileged(Native Method) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380) at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:264) at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) - locked <0x595b3af0> (a java.util.concurrent.ConcurrentHashMap) at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:261) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164) at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:429) - locked <0x595b3b18> (a java.util.concurrent.ConcurrentHashMap) at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:728) at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext.access$1600(AbstractDelegatedExecutionApplicationContext.java:69) at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext$4.run(AbstractDelegatedExecutionApplicationContext.java:355) - locked <0x595b3be0> (a java.lang.Object) at org.springframework.osgi.util.internal.PrivilegedUtils.executeWithCustomTCCL(PrivilegedUtils.java:85) at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext.completeRefresh(AbstractDelegatedExecutionApplicationContext.java:320) at org.springframework.osgi.extender.internal.dependencies.startup.DependencyWaiterApplicationContextExecutor$CompleteRefreshTask.run(DependencyWaiterApplicationContextExecutor.java:136) at java.lang.Thread.run(Thread.java:619) Locked ownable synchronizers: - None "RMI TCP Connection(idle)" daemon prio=6 tid=0x05329400 nid=0x1100 waiting on condition [0x069af000..0x069afa14] java.lang.Thread.State: TIMED_WAITING (parking) at sun.misc.Unsafe.park(Native Method) - parking to wait for <0x200a1380> (a java.util.concurrent.SynchronousQueue$TransferStack) at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:198) at java.util.concurrent.SynchronousQueue$TransferStack.awaitFulfill(SynchronousQueue.java:424) at java.util.concurrent.SynchronousQueue$TransferStack.transfer(SynchronousQueue.java:323) at java.util.conCurrent.SynchronousQueue.poll(SynchronousQueue.java:874) at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:945) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907) at java.lang.Thread.run(Thread.java:619) Locked ownable synchronizers: - None "Timer-4" daemon prio=6 tid=0x053aa400 nid=0xfa4 in Object.wait() [0x06eef000..0x06eefc94] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x59585388> (a java.util.TaskQueue) at java.lang.Object.wait(Object.java:485) at java.util.TimerThread.mainLoop(Timer.java:483) - locked <0x59585388> (a java.util.TaskQueue) at java.util.TimerThread.run(Timer.java:462) Locked ownable synchronizers: - None "weblogic.timers.TimerThread" daemon prio=10 tid=0x05151800 nid=0x11fc in Object.wait() [0x06e9f000..0x06e9fd14] java.lang.Thread.State: TIMED_WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x5959c3c0> (a weblogic.timers.internal.TimerThread) at weblogic.timers.internal.TimerThread$Thread.run(TimerThread.java:267) - locked <0x5959c3c0> (a weblogic.timers.internal.TimerThread) Locked ownable synchronizers: - None "ExecuteThread: '4' for queue: 'default'" daemon prio=6 tid=0x04880c00 nid=0x117c in Object.wait() [0x06e4f000..0x06e4fd94] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x595855a8> (a weblogic.kernel.ServerExecuteThread) at java.lang.Object.wait(Object.java:485) at weblogic.kernel.ExecuteThread.waitForRequest(ExecuteThread.java:91) - locked <0x595855a8> (a weblogic.kernel.ServerExecuteThread) at weblogic.kernel.ExecuteThread.run(ExecuteThread.java:115) Locked ownable synchronizers: - None "ExecuteThread: '3' for queue: 'default'" daemon prio=6 tid=0x05242400 nid=0xd34 in Object.wait() [0x06dff000..0x06dffa14] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x59585998> (a weblogic.kernel.ServerExecuteThread) at java.lang.Object.wait(Object.java:485) at weblogic.kernel.ExecuteThread.waitForRequest(ExecuteThread.java:91) - locked <0x59585998> (a weblogic.kernel.ServerExecuteThread) at weblogic.kernel.ExecuteThread.run(ExecuteThread.java:115) Locked ownable synchronizers: - None "ExecuteThread: '2' for queue: 'default'" daemon prio=6 tid=0x04509800 nid=0x1600 in Object.wait() [0x06daf000..0x06dafa94] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x59585c78> (a weblogic.kernel.ServerExecuteThread) at java.lang.Object.wait(Object.java:485) at weblogic.kernel.ExecuteThread.waitForRequest(ExecuteThread.java:91) - locked <0x59585c78> (a weblogic.kernel.ServerExecuteThread) at weblogic.kernel.ExecuteThread.run(ExecuteThread.java:115) Locked ownable synchronizers: - None "ExecuteThread: '1' for queue: 'default'" daemon prio=6 tid=0x05170800 nid=0x894 in Object.wait() [0x06d5f000..0x06d5fb14] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x59585f58> (a weblogic.kernel.ServerExecuteThread) at java.lang.Object.wait(Object.java:485) at weblogic.kernel.ExecuteThread.waitForRequest(ExecuteThread.java:91) - locked <0x59585f58> (a weblogic.kernel.ServerExecuteThread) at weblogic.kernel.ExecuteThread.run(ExecuteThread.java:115) Locked ownable synchronizers: - None "ExecuteThread: '0' for queue: 'default'" daemon prio=6 tid=0x05329800 nid=0x10a8 in Object.wait() [0x06c1f000..0x06c1fb94] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x59586238> (a weblogic.kernel.ServerExecuteThread) at java.lang.Object.wait(Object.java:485) at weblogic.kernel.ExecuteThread.waitForRequest(ExecuteThread.java:91) - locked <0x59586238> (a weblogic.kernel.ServerExecuteThread) at weblogic.kernel.ExecuteThread.run(ExecuteThread.java:115) Locked ownable synchronizers: - None "Timer-3" daemon prio=6 tid=0x0484bc00 nid=0xebc waiting for monitor entry [0x06cbf000..0x06cbfa94] java.lang.Thread.State: BLOCKED (on object monitor) at org.springframework.osgi.extender.internal.dependencies.startup.DependencyWaiterApplicationContextExecutor.close(DependencyWaiterApplicationContextExecutor.java:355) - waiting to lock <0x595b3be0> (a java.lang.Object) - locked <0x595b3c48> (a java.lang.Object) at org.springframework.osgi.context.support.AbstractDelegatedExecutionApplicationContext.doClose(AbstractDelegatedExecutionApplicationContext.java:236) at org.springframework.context.support.AbstractApplicationContext.close(AbstractApplicationContext.java:794) - locked <0x595b4128> (a java.lang.Object) at org.springframework.osgi.extender.internal.activator.ContextLoaderListener$3.run(ContextLoaderListener.java:807) at org.springframework.osgi.extender.internal.util.concurrent.RunnableTimedExecution$MonitoredRunnable.run(RunnableTimedExecution.java:60) at org.springframework.scheduling.timer.DelegatingTimerTask.run(DelegatingTimerTask.java:66) at java.util.TimerThread.mainLoop(Timer.java:512) at java.util.TimerThread.run(Timer.java:462) Locked ownable synchronizers: - None "Timer-2" daemon prio=6 tid=0x04780400 nid=0x1388 in Object.wait() [0x06c6f000..0x06c6fb14] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x20783b60> (a java.util.TaskQueue) at java.lang.Object.wait(Object.java:485) at java.util.TimerThread.mainLoop(Timer.java:483) - locked <0x20783b60> (a java.util.TaskQueue) at java.util.TimerThread.run(Timer.java:462) Locked ownable synchronizers: - None "AWT-Windows" daemon prio=6 tid=0x04028000 nid=0x83c runnable [0x06b8f000..0x06b8fb14] java.lang.Thread.State: RUNNABLE at sun.awt.windows.WToolkit.eventLoop(Native Method) at sun.awt.windows.WToolkit.run(WToolkit.java:291) at java.lang.Thread.run(Thread.java:619) Locked ownable synchronizers: - None "Java2D Disposer" daemon prio=10 tid=0x0469c400 nid=0x1164 in Object.wait() [0x0695f000..0x0695fc14] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x206f4200> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:116) - locked <0x206f4200> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:132) at sun.java2d.Disposer.run(Disposer.java:125) at java.lang.Thread.run(Thread.java:619) Locked ownable synchronizers: - None "NioSocketAcceptor-1" prio=6 tid=0x055acc00 nid=0xf80 runnable [0x068bf000..0x068bfd94] java.lang.Thread.State: RUNNABLE at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(Native Method) at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll(WindowsSelectorImpl.java:274) at sun.nio.ch.WindowsSelectorImpl$SubSelector.access$400(WindowsSelectorImpl.java:256) at sun.nio.ch.WindowsSelectorImpl.doSelect(WindowsSelectorImpl.java:137) at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:69) - locked <0x2069e820> (a sun.nio.ch.Util$1) - locked <0x2069e810> (a java.util.Collections$UnmodifiableSet) - locked <0x2069e3d8> (a sun.nio.ch.WindowsSelectorImpl) at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:80) at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:84) at org.apache.mina.transport.socket.nio.NioSocketAcceptor.select(NioSocketAcceptor.java:288) at org.apache.mina.core.polling.AbstractPollingIoAcceptor$Acceptor.run(AbstractPollingIoAcceptor.java:402) at org.apache.mina.util.NamePreservingRunnable.run(NamePreservingRunnable.java:64) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) at java.lang.Thread.run(Thread.java:619) Locked ownable synchronizers: - <0x2069e0f8> (a java.util.concurrent.locks.ReentrantLock$NonfairSync) "RMI RenewClean-[192.168.114.60:1640]" daemon prio=6 tid=0x05312400 nid=0x1058 in Object.wait() [0x06b3f000..0x06b3fa94] java.lang.Thread.State: TIMED_WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x20669858> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:116) - locked <0x20669858> (a java.lang.ref.ReferenceQueue$Lock) at sun.rmi.transport.DGCClient$EndpointEntry$RenewCleanThread.run(DGCClient.java:516) at java.lang.Thread.run(Thread.java:619) Locked ownable synchronizers: - None "RMI Scheduler(0)" daemon prio=6 tid=0x05132800 nid=0x146c waiting on condition [0x06aef000..0x06aefb14] java.lang.Thread.State: TIMED_WAITING (parking) at sun.misc.Unsafe.park(Native Method) - parking to wait for <0x200a1508> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject) at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:198) at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:1963) at java.util.concurrent.DelayQueue.take(DelayQueue.java:164) at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:583) at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:576) at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:947) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907) at java.lang.Thread.run(Thread.java:619) Locked ownable synchronizers: - None "GC Daemon" daemon prio=2 tid=0x05678400 nid=0x166c in Object.wait() [0x06a9f000..0x06a9fc14] java.lang.Thread.State: TIMED_WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x2060d790> (a sun.misc.GC$LatencyLock) at sun.misc.GC$Daemon.run(GC.java:100) - locked <0x2060d790> (a sun.misc.GC$LatencyLock) Locked ownable synchronizers: - None "RMI Reaper" prio=6 tid=0x04fee800 nid=0x828 in Object.wait() [0x06a4f000..0x06a4fd14] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x200a79c8> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:116) - locked <0x200a79c8> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:132) at sun.rmi.transport.ObjectTable$Reaper.run(ObjectTable.java:333) at java.lang.Thread.run(Thread.java:619) Locked ownable synchronizers: - None "RMI TCP Accept-0" daemon prio=6 tid=0x0488dc00 nid=0x129c runnable [0x069ff000..0x069ffc94] java.lang.Thread.State: RUNNABLE at java.net.PlainSocketImpl.socketAccept(Native Method) at java.net.PlainSocketImpl.accept(PlainSocketImpl.java:384) - locked <0x20606780> (a java.net.SocksSocketImpl) at java.net.ServerSocket.implAccept(ServerSocket.java:453) at java.net.ServerSocket.accept(ServerSocket.java:421) at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.executeAcceptLoop(TCPTransport.java:369) at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.run(TCPTransport.java:341) at java.lang.Thread.run(Thread.java:619) Locked ownable synchronizers: - None "RMI TCP Accept-20220" daemon prio=6 tid=0x05319800 nid=0x1634 runnable [0x0690f000..0x0690fa94] java.lang.Thread.State: RUNNABLE at java.net.PlainSocketImpl.socketAccept(Native Method) at java.net.PlainSocketImpl.accept(PlainSocketImpl.java:384) - locked <0x205fb908> (a java.net.SocksSocketImpl) at java.net.ServerSocket.implAccept(ServerSocket.java:453) at java.net.ServerSocket.accept(ServerSocket.java:421) at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.executeAcceptLoop(TCPTransport.java:369) at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.run(TCPTransport.java:341) at java.lang.Thread.run(Thread.java:619) Locked ownable synchronizers: - None "gogo shell pipe thread" daemon prio=6 tid=0x0511f400 nid=0x920 runnable [0x0586f000..0x0586fb94] java.lang.Thread.State: RUNNABLE at jline.WindowsTerminal.readByte(Native Method) at jline.WindowsTerminal.readCharacter(WindowsTerminal.java:237) at jline.AnsiWindowsTerminal.readDirectChar(AnsiWindowsTerminal.java:44) at org.apache.felix.karaf.shell.console.jline.Console$Pipe.run(Console.java:346) at java.lang.Thread.run(Thread.java:619) Locked ownable synchronizers: - None "Karaf Shell Console Thread" prio=6 tid=0x05134400 nid=0xf54 waiting on condition [0x0581f000..0x0581fc14] java.lang.Thread.State: WAITING (parking) at sun.misc.Unsafe.park(Native Method) - parking to wait for <0x20573970> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject) at java.util.concurrent.locks.LockSupport.park(LockSupport.java:158) at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1925) at java.util.concurrent.ArrayBlockingQueue.take(ArrayBlockingQueue.java:317) at org.apache.felix.karaf.shell.console.jline.Console$ConsoleInputStream.read(Console.java:286) at org.apache.felix.karaf.shell.console.jline.Console$ConsoleInputStream.read(Console.java:303) at jline.AnsiWindowsTerminal.readCharacter(AnsiWindowsTerminal.java:40) at jline.WindowsTerminal.readVirtualKey(WindowsTerminal.java:359) at jline.ConsoleReader.readVirtualKey(ConsoleReader.java:1504) at jline.ConsoleReader.readBinding(ConsoleReader.java:674) at jline.ConsoleReader.readLine(ConsoleReader.java:514) at jline.ConsoleReader.readLine(ConsoleReader.java:468) at org.apache.felix.karaf.shell.console.jline.Console.run(Console.java:169) at java.lang.Thread.run(Thread.java:619) Locked ownable synchronizers: - None "pool-2-thread-3" prio=6 tid=0x04522c00 nid=0xf7c waiting on condition [0x04f9f000..0x04f9fc94] java.lang.Thread.State: WAITING (parking) at sun.misc.Unsafe.park(Native Method) - parking to wait for <0x202a6220> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject) at ja

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• Error in destroying object in Box2D/LibGDX

  - by Crypted

  I'm trying to delete an object when a collision happens. I have put the following code in the render method of the object so it would be outside of the physics calculations. public void render(SpriteBatch spriteBatch) { // some other code... body.setActive(false); body.getWorld().destroyBody(body); But I'm getting an run-time error which crashes the JVM and shows, AL lib: alc_cleanup: 1 device not closed Assertion failed! Program: C:\Program Files\Java\jre6\bin\javaw.exe File: /var/lib/hudson/jobs/libgdx-git/workspace/gdx/jni/Box2D/Dynamics/b2World.cpp, Line 133 Expression: m_bodyCount 0 Can anyone help me here?

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• Using MVP, how to create a view from another view, linked with the same model object

  - by Dinaiz

  Background We use the Model-View-Presenter design pattern along with the abstract factory pattern and the "signal/slot" pattern in our application, to fullfill 2 main requirements Enhance testability (very lightweight GUI, every action can be simulated in unit tests) Make the "view" totally independant from the rest, so we can change the actual view implementation, without changing anything else In order to do so our code is divided in 4 layers : Core : which holds the model Presenter : which manages interactions between the view interfaces (see bellow) and the core View Interfaces : they define the signals and slots for a View, but not the implementation Views : the actual implementation of the views When the presenter creates or deals with views, it uses an abstract factory and only knows about the view interfaces. It does the signal/slot binding between views interfaces. It doesn't care about the actual implementation. In the "views" layer, we have a concrete factory which deals with implementations. The signal/slot mechanism is implemented using a custom framework built upon boost::function. Really, what we have is something like that : http://martinfowler.com/eaaDev/PassiveScreen.html Everything works fine. The problem However, there's a problem I don't know how to solve. Let's take for example a very simple drag and drop example. I have two ContainersViews (ContainerView1, ContainerView2). ContainerView1 has an ItemView1. I drag the ItemView1 from ContainerView1 to ContainerView2. ContainerView2 must create an ItemView2, of a different type, but which "points" to the same model object as ItemView1. So the ContainerView2 gets a callback called for the drop action with ItemView1 as a parameter. It calls ContainerPresenterB passing it ItemViewB In this case we are only dealing with views. In MVP-PV, views aren't supposed to know anything about the presenter nor the model, right ? How can I create the ItemView2 from the ItemView1, not knowing which model object is ItemView1 representing ? I thought about adding an "itemId" to every view, this id being the id of the core object the view represents. So in pseudo code, ContainerPresenter2 would do something like itemView2=abstractWidgetFactory.createItemView2(); this.add(itemView2,itemView1.getCoreObjectId()) I don't get too much into details. That just work. The problem I have here is that those itemIds are just like pointers. And pointers can be dangling. Imagine that by mistake, I delete itemView1, and this deletes coreObject1. The itemView2 will have a coreObjectId which represents an invalid coreObject. Isn't there a more elegant and "bulletproof" solution ? Even though I never did ObjectiveC or macOSX programming, I couldn't help but notice that our framework is very similar to Cocoa framework. How do they deal with this kind of problem ? Couldn't find more in-depth information about that on google. If someone could shed some light on this. I hope this question isn't too confusing ...

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• What are the most important OO skills to show off in the job hunt?

  - by Kat

  I am in the market for new employment, and found a position were they asked me to create a programming sample based off an assignment. I blew the sample trying to get it done quickly one night, and got declined - only to be given a second chance recently. The concern was that I didn't really demonstrate object oriented knowledge. I've rethought my approach but I figure it's worth asking: if you were hiring someone for an OO position, what skills would you most want to see them demonstrate they had a firm grasp on? I want to be sure that I'm missing anything important this time around.

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• HTML Javascript Hidden Object or Photo Hunt Game

  - by PeteT

  Is anyone aware of any example photo hunt/hidden object games either in HTML and Javascript or flash if necessary? I am having trouble finding one, I may be using the wrong words to search. Photo hunt being like the wheres wally/waldo books where you look for wally in a complex image until you find him. So if it were played on screen you would press the location of wally and it would either be correct or wrong, possibly timed. I am hoping to find one where you can just load in your own photos and specify some co-ordinates that match where the hidden object is. A spot the difference example may be useful as a starting point but I haven't found an example of either that is web based yet.

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• Are CK Metrics still considered useful? Is there an open source tool to help?

  - by DeveloperDon

  Chidamber & Kemerer proposed several metrics for object oriented code. Among them, depth of inheritance tree, weighted number of methods, number of member functions, number of children, and coupling between objects. Using a base of code, they tried to correlated these metrics to the defect density and maintenance effort using covariant analysis. Are these metrics actionable in projects? Perhaps they can guide refactoring. For example weighted number of methods might show which God classes needed to be broken into more cohesive classes that address a single concern. Is there approach superseded by a better method, and is there a tool that can identify problem code, particularly in moderately large project being handed off to a new developer or team?

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• Where does this concept of "favor composition over inheritance" come from?

  - by Mason Wheeler

  In the last few months, the mantra "favor composition over inheritance" seems to have sprung up out of nowhere and become almost some sort of meme within the programming community. And every time I see it, I'm a little bit mystified. It's like someone said "favor drills over hammers." In my experience, composition and inheritance are two different tools with different use cases, and treating them as if they were interchangeable and one was inherently superior to the other makes no sense. Also, I never see a real explanation for why inheritance is bad and composition is good, which just makes me more suspicious. Is it supposed to just be accepted on faith? Liskov substitution and polymorphism have well-known, clear-cut benefits, and IMO comprise the entire point of using object-oriented programming, and no one ever explains why they should be discarded in favor of composition. Does anyone know where this concept comes from, and what the rationale behind it is?

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• Need advice on design in Ruby On Rails

  - by Elad

  For personal educational purposes I am making a site for a conference. One of the object that exist in a conference is a session, which has different states and in each state it has slightly different attributes: When submitted it has a speaker (User in the system), Title and abstract. When under review it has reviews and comments (in addition to the basic data) When accepted it has a defined time-slot but no reviewers anymore. I feel that it is not the best thing to add a "status" attributes and start adding many if statements... So I thought it would be better to have different classes for each state each with it's own validations and behaviors. What do you think about this design? Do you have a better idea? *I must add this out of frustration: I had several edits of the question, including one major change but no one actually gave any hint or clue on which direction should i take or where is a better place to ask this... Hardly helpful.

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• When should a method of a class return the same instance after modifying itself?

  - by modiX

  I have a class that has three methods A(), B() and C(). Those methods modify the own instance. While the methods have to return an instance when the instance is a separate copy (just as Clone()), I got a free choice to return void or the same instance (return this;) when modifying the same instance in the method and not returning any other value. When deciding for returning the same modified instance, I can do neat method chains like obj.A().B().C();. Would this be the only reason for doing so? Is it even okay to modify the own instance and return it, too? Or should it only return a copy and leave the original object as before? Because when returning the same modified instance the user would maybe admit the returned value is a copy, otherwise it would not be returned? If it's okay, what's the best way to clarify such things on the method?

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• cocos2d-x - object creation and management in game design

  - by Jason

  How do others keep track of everything going on in their games? I am working on a new game and I am quickly realizing everything that I need to keep track of. Example: Maybe a layerManager that keeps track of all the layers and what is happening for a particular scene. Maybe a sceneManager for sharing objects among scenes But then getting to game play itself, what if you have 100 objects on the screen each with its own state and happenings, there needs tobe a way to keep track of all of that. Drawing everything out is really helping me. Can anyone share with me how they go about object tracking/management? I am seeing a few different managers and then maybe even a parent object that manages the managers..is my thinking way off? Any design patterns that may be useful for me to read about? Update: doing some reading and maybe a Factory pattern might apply.

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