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  • 10 Reasons Why Java is the Top Embedded Platform

    - by Roger Brinkley
    With the release of Oracle ME Embedded 3.2 and Oracle Java Embedded Suite, Java is now ready to fully move into the embedded developer space, what many have called the "Internet of Things". Here are 10 reasons why Java is the top embedded platform. 1. Decouples software development from hardware development cycle Development is typically split between both hardware and software in a traditional design flow . This leads to complicated co-design and requires prototype hardware to be built. This parallel and interdependent hardware / software design process typically leads to two or more re-development phases. With Embedded Java, all specific work is carried out in software, with the (processor) hardware implementation fully decoupled. This with eliminate or at least reduces the need for re-spins of software or hardware and the original development efforts can be carried forward directly into product development and validation. 2. Development and testing can be done (mostly) using standard desktop systems through emulation Because the software and hardware are decoupled it now becomes easier to test the software long before it reaches the hardware through hardware emulation. Emulation is the ability of a program in an electronic device to imitate another program or device. In the past Java tools like the Java ME SDK and the SunSPOTs Solarium provided developers with emulation for a complete set of mobile telelphones and SunSpots. This often included network interaction or in the case of SunSPOTs radio communication. What emulation does is speed up the development cycle by refining the software development process without the need of hardware. The software is fixed, redefined, and refactored without the timely expense of hardware testing. With tools like the Java ME 3.2 SDK, Embedded Java applications can be be quickly developed on Windows based platforms. In the end of course developers should do a full set of testing on the hardware as incompatibilities between emulators and hardware will exist, but the amount of time to do this should be significantly reduced. 3. Highly productive language, APIs, runtime, and tools mean quick time to market Charles Nutter probably said it best in twitter blog when he tweeted, "Every time I see a piece of C code I need to port, my heart dies a little. Then I port it to 1/4 as much Java, and feel better." The Java environment is a very complex combination of a Java Virtual Machine, the Java Language, and it's robust APIs. Combine that with the Java ME SDK for small devices or just Netbeans for the larger devices and you have a development environment where development time is reduced significantly meaning the product can be shipped sooner. Of course this is assuming that the engineers don't get slap happy adding new features given the extra time they'll have.  4. Create high-performance, portable, secure, robust, cross-platform applications easily The latest JIT compilers for the Oracle JVM approach the speed of C/C++ code, and in some memory allocation intensive circumstances, exceed it. And specifically for the embedded devices both ME Embedded and SE Embedded have been optimized for the smaller footprints.  In portability Java uses Bytecode to make the language platform independent. This creates a write once run anywhere environment that allows you to develop on one platform and execute on others and avoids a platform vendor lock in. For security, Java achieves protection by confining a Java program to a Java execution environment and not allowing it to access other parts of computer.  In variety of systems the program must execute reliably to be robust. Finally, Oracle Java ME Embedded is a cross-industry and cross-platform product optimized in release version 3.2 for chipsets based on the ARM architectures. Similarly Oracle Java SE Embedded works on a variety of ARM V5, V6, and V7, X86 and Power Architecture Linux. 5. Java isolates your apps from language and platform variations (e.g. C/C++, kernel, libc differences) This has been a key factor in Java from day one. Developers write to Java and don't have to worry about underlying differences in the platform variations. Those platform variations are being managed by the JVM. Gone are the C/C++ problems like memory corruptions, stack overflows, and other such bugs which are extremely difficult to isolate. Of course this doesn't imply that you won't be able to get away from native code completely. There could be some situations where you have to write native code in either assembler or C/C++. But those instances should be limited. 6. Most popular embedded processors supported allowing design flexibility Java SE Embedded is now available on ARM V5, V6, and V7 along with Linux on X86 and Power Architecture platforms. Java ME Embedded is available on system based on ARM architecture SOCs with low memory footprints and a device emulation environment for x86/Windows desktop computers, integrated with the Java ME SDK 3.2. A standard binary of Oracle Java ME Embedded 3.2 for ARM KEIL development boards based on ARM Cortex M-3/4 (KEIL MCBSTM32F200 using ST Micro SOC STM32F207IG) will soon be available for download from the Oracle Technology Network (OTN). 7. Support for key embedded features (low footprint, power mgmt., low latency, etc) All embedded devices by there very nature are constrained in some way. Economics may dictate a device with a less RAM and ROM. The CPU needs can dictate a less powerful device. Power consumption is another major resource in some embedded devices as connecting to consistent power source not always desirable or possible. For others they have to constantly on. Often many of these systems are headless (in the embedded space it's almost always Halloween).  For memory resources ,Java ME Embedded can run in environment as low as 130KB RAM/350KB ROM for a minimal, customized configuration up to 700KB RAM/1500KB ROM for the full, standard configuration. Java SE Embedded is designed for environments starting at 32MB RAM/39MB  ROM. Key functionality of embedded devices such as auto-start and recovery, flexible networking are fully supported. And while Java SE Embedded has been optimized for mid-range to high-end embedded systems, Java ME Embedded is a Java runtime stack optimized for small embedded systems. It provides a robust and flexible application platform with dedicated embedded functionality for always-on, headless (no graphics/UI), and connected devices. 8. Leverage huge Java developer ecosystem (expertise, existing code) There are over 9 million developers in world that work on Java, and while not all of them work on embedded systems, their wealth of expertise in developing applications is immense. In short, getting a java developer to work on a embedded system is pretty easy, you probably have a java developer living in your subdivsion.  Then of course there is the wealth of existing code. The Java Embedded Community on Java.net is central gathering place for embedded Java developers. Conferences like Embedded Java @ JavaOne and the a variety of hardware vendor conferences like Freescale Technlogy Forums offer an excellent opportunity for those interested in embedded systems. 9. Easily create end-to-end solutions integrated with Java back-end services In the "Internet of Things" things aren't on an island doing an single task. For instance and embedded drink dispenser doesn't just dispense a beverage, but could collect money from a credit card and also send information about current sales. Similarly, an embedded house power monitoring system doesn't just manage the power usage in a house, but can also send that data back to the power company. In both cases it isn't about the individual thing, but monitoring a collection of  things. How much power did your block, subdivsion, area of town, town, county, state, nation, world use? How many Dr Peppers were purchased from thing1, thing2, thingN? The point is that all this information can be collected and transferred securely  (and believe me that is key issue that Java fully supports) to back end services for further analysis. And what better back in service exists than a Java back in service. It's interesting to note that on larger embedded platforms that support the Java Embedded Suite some of the analysis might be done on the embedded device itself as JES has a glassfish server and Java Database as part of the installation. The result is an end to end Java solution. 10. Solutions from constrained devices to server-class systems Just take a look at some of the embedded Java systems that have already been developed and you'll see a vast range of solutions. Livescribe pen, Kindle, each and every Blu-Ray player, Cisco's Advanced VOIP phone, KronosInTouch smart time clock, EnergyICT smart metering, EDF's automated meter management, Ricoh Printers, and Stanford's automated car  are just a few of the list of embedded Java implementation that continues to grow. Conclusion Now if your a Java Developer you probably look at some of the 10 reasons and say "duh", but for the embedded developers this is should be an eye opening list. And with the release of ME Embedded 3.2 and the Java Embedded Suite the embedded developers life is now a whole lot easier. For the Java developer your employment opportunities are about to increase. For both it's a great time to start developing Java for the "Internet of Things".

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  • Getting a design company to embrace the benefits of good development

    - by Toby
    I know there are already various topics discussing what we can do to get managers to buy into good development practices, but I was wondering if there are any specific things we can do to explain to designers that Web Development is more than just turning their design into a website. I want to try and push them to design based on progressive enhancement, responsive design and ajax but I think there is a trend to stick to the print based design principles, which is understandable as it is their background, but is frustrating to a dev.

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  • Java EE 6: How to get module name and app name

    - by user12798506
    Java EE 6??????????????????????????????????????????????? ???????????????[1] ?????????????JNDI???????????????????"java:module/ModuleName"?????? ?????"java:app/AppName"???????? InitialContext ctx = new InitialContext(); String moduleName = ctx.lookup("java:module/ModuleName"); // ?????? String appName = ctx.lookup("java:app/AppName"); // ????????? ???@Resource?????????????????????????????????????????? @Resource(lookup="java:module/ModuleName") String moduleName; // ?????????????????? @Resource(lookup="java:app/AppName") String appName; // ????????????????????? ???EAR???????Web????????EJB??????????????????AppName???????????????? ?????????GlassFish V3 (3.1.2.2)?WebLogic 12c (12.1.1)?JBoss AS 7 (7.1.1)?????????? ????????????????AppName???ModuleName??????????????? ?????????Web Profile??????????????????(GlassFish?JBoss?????Web Profile ?????)?????Apache TomEE (1.5.0)????????ModuleName???"localhost/<Web?????? >"?????????????????????????????????????? Java EE 6??????????????????????????????????????????????? ??????????????????????????????????????????????????? ???????????????????????????????????????????????????? ???????? ???Apache Tomcat 7.0?Servlet 3.0??????????????????????????????·??? ???????JNDI???????????????????????? ??:?Tomcat????????Java EE?????????????????????? [1] Java EE 6????(JSR 316)????????????? (pp.122-123): EE.5.15 Application Name and Module Name References A component may access the name of the current application using the pre-defined JNDI name java:app/AppName. A component may access the name of the current module using the pre-defined JNDI name java:module/ModuleName. Both of these names are represented by String objects.

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  • SSIS Design Pattern: Producing a Footer Row

    - by andyleonard
    The following is an excerpt from SSIS Design Patterns (now available in the UK!) Chapter 7, Flat File Source Patterns. The only planned appearance of all five authors presenting on SSIS Design Patterns is the SSIS Design Patterns day-long pre-conference session at the PASS Summit 2012 . Register today . Let’s look at producing a footer row and adding it to the data file. For this pattern, we will leverage project and package parameters. We will also leverage the Parent-Child pattern, which will be...(read more)

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  • Making a design for a Problem [closed]

    - by Vaibhav Agarwal
    I have written many codes using OOPS and I am still to understand when is a code good enough to be accepted by experts. The thought procedure of every man is different and so is the design. My question is should I do something in particular to design my programs in such a way that they are good enough to be accepted by people. Other thing I have also read Head First Object Oriented Design but at last I feel that the way they design the problems is much different I would have designed them.

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  • When to use functional programming approach and when not? (in Java)

    - by john smith optional
    let's assume I have a task to create a Set of class names. To remove duplication of .getName() method calls for each class, I used org.apache.commons.collections.CollectionUtils and org.apache.commons.collections.Transformer as follows: Snippet 1: Set<String> myNames = new HashSet<String>(); CollectionUtils.collect( Arrays.<Class<?>>asList(My1.class, My2.class, My3.class, My4.class, My5.class), new Transformer() { public Object transform(Object o) { return ((Class<?>) o).getName(); } }, myNames); An alternative would be this code: Snippet 2: Collections.addAll(myNames, My1.class.getName(), My2.class.getName(), My3.class.getName(), My4.class.getName(), My5.class.getName()); So, when using functional programming approach is overhead and when it's not and why? Isn't my usage of functional programming approach in snippet 1 is an overhead and why?

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  • How do you deal with design in Scrum?

    - by Seth
    How do you deal with design in Scrum? Do you still have well written design documents for each scrum iteration? Do you just do design notes featuring UML diagrams? Or do you just have well commented code? Each iteration may involve changing design so I just wanted to know how people capture this so new developers have an easy job of understanding the domain and getting on board as rapidly as possible.

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  • How do you deal with design in Scrum?

    - by Seth
    How do you deal with design in Scrum? Do you still have well written design documents for each scrum iteration? Do you just do design notes featuring UML diagrams? Or do you just have well commented code? Each iteration may involve changing design so I just wanted to know how people capture this so new developers have an easy job of understanding the domain and getting on board as rapidly as possible.

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  • Arquillian - Weld SE - getting NullPointerException

    - by Walter White
    I am new to Arquillian and want to get some basic testing working (inject a bean and assert it does something). Exception: ------------------------------------------------------------------------------- Test set: com.walterjwhite.test.TestCase ------------------------------------------------------------------------------- Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 1.231 sec <<< FAILURE! test(com.walterjwhite.test.TestCase) Time elapsed: 0.02 sec <<< ERROR! java.lang.RuntimeException: Could not inject members at org.jboss.arquillian.testenricher.cdi.CDIInjectionEnricher.injectClass(CDIInjectionEnricher.java:113) at org.jboss.arquillian.testenricher.cdi.CDIInjectionEnricher.enrich(CDIInjectionEnricher.java:61) at org.jboss.arquillian.impl.enricher.ClientTestEnricher.enrich(ClientTestEnricher.java:61) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:616) at org.jboss.arquillian.impl.core.ObserverImpl.invoke(ObserverImpl.java:90) at org.jboss.arquillian.impl.core.EventContextImpl.invokeObservers(EventContextImpl.java:98) at org.jboss.arquillian.impl.core.EventContextImpl.proceed(EventContextImpl.java:80) at org.jboss.arquillian.impl.client.ContainerDeploymentContextHandler.createContext(ContainerDeploymentContextHandler.java:133) at org.jboss.arquillian.impl.client.ContainerDeploymentContextHandler.createBeforeContext(ContainerDeploymentContextHandler.java:115) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:616) at org.jboss.arquillian.impl.core.ObserverImpl.invoke(ObserverImpl.java:90) at org.jboss.arquillian.impl.core.EventContextImpl.proceed(EventContextImpl.java:87) at org.jboss.arquillian.impl.TestContextHandler.createTestContext(TestContextHandler.java:82) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:616) at org.jboss.arquillian.impl.core.ObserverImpl.invoke(ObserverImpl.java:90) at org.jboss.arquillian.impl.core.EventContextImpl.proceed(EventContextImpl.java:87) at org.jboss.arquillian.impl.TestContextHandler.createClassContext(TestContextHandler.java:68) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:616) at org.jboss.arquillian.impl.core.ObserverImpl.invoke(ObserverImpl.java:90) at org.jboss.arquillian.impl.core.EventContextImpl.proceed(EventContextImpl.java:87) at org.jboss.arquillian.impl.TestContextHandler.createSuiteContext(TestContextHandler.java:54) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:616) at org.jboss.arquillian.impl.core.ObserverImpl.invoke(ObserverImpl.java:90) at org.jboss.arquillian.impl.core.EventContextImpl.proceed(EventContextImpl.java:87) at org.jboss.arquillian.impl.core.ManagerImpl.fire(ManagerImpl.java:126) at org.jboss.arquillian.impl.core.ManagerImpl.fire(ManagerImpl.java:106) at org.jboss.arquillian.impl.EventTestRunnerAdaptor.before(EventTestRunnerAdaptor.java:85) at org.jboss.arquillian.junit.Arquillian$4.evaluate(Arquillian.java:210) at org.jboss.arquillian.junit.Arquillian.multiExecute(Arquillian.java:303) at org.jboss.arquillian.junit.Arquillian.access$300(Arquillian.java:45) at org.jboss.arquillian.junit.Arquillian$5.evaluate(Arquillian.java:228) at org.junit.runners.BlockJUnit4ClassRunner.runNotIgnored(BlockJUnit4ClassRunner.java:79) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:71) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:49) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184) at org.jboss.arquillian.junit.Arquillian$2.evaluate(Arquillian.java:173) at org.jboss.arquillian.junit.Arquillian.multiExecute(Arquillian.java:303) at org.jboss.arquillian.junit.Arquillian.access$300(Arquillian.java:45) at org.jboss.arquillian.junit.Arquillian$3.evaluate(Arquillian.java:187) at org.junit.runners.ParentRunner.run(ParentRunner.java:236) at org.jboss.arquillian.junit.Arquillian.run(Arquillian.java:127) at org.apache.maven.surefire.junit4.JUnit4TestSet.execute(JUnit4TestSet.java:35) at org.apache.maven.surefire.junit4.JUnit4Provider.executeTestSet(JUnit4Provider.java:115) at org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:97) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:616) at org.apache.maven.surefire.booter.ProviderFactory$ClassLoaderProxy.invoke(ProviderFactory.java:103) at $Proxy0.invoke(Unknown Source) at org.apache.maven.surefire.booter.SurefireStarter.invokeProvider(SurefireStarter.java:150) at org.apache.maven.surefire.booter.SurefireStarter.runSuitesInProcess(SurefireStarter.java:91) at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:69) Caused by: java.lang.NullPointerException at org.jboss.arquillian.testenricher.cdi.CDIInjectionEnricher.getBeanManager(CDIInjectionEnricher.java:51) at org.jboss.arquillian.testenricher.cdi.CDIInjectionEnricher.injectClass(CDIInjectionEnricher.java:100) ... 71 more TestCase class @RunWith(Arquillian.class) public class TestCase { @Deployment public static JavaArchive createDeployment() { return ShrinkWrap.create(JavaArchive.class).addClasses(TestEntity.class, Implementation.class) .addAsManifestResource(EmptyAsset.INSTANCE, ArchivePaths.create("beans.xml")); } @Inject Implementation implementation; @Test public void test() throws Exception { final TestEntity testEntity = implementation.create(); Assert.assertNotNull(testEntity); } } When I run this, I get a NullPointerException, the bean manager is null. It looks like I am missing a step, but from the examples, it looks like this is all I should need. Any ideas? Walter

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  • AppEngine JRuby - OutOfMemoryError: Java heap space - can it be solved?

    - by elado
    I use AppEngine JRuby on Rails (SDK version 1.3.3.1) - a problem I encounter often is that after a few requests the server is getting really SLOW, until it dies and throws OutOfMemoryError on the terminal (OSX). The requests themselves are very lightweight, not more than looking for an entity or saving it, using DataMapper. On appspot, this problem is not happening. Is there any way to enlarge the heap space for JRuby? The exception log: Exception in thread "Timer-2" java.lang.OutOfMemoryError: Java heap space Apr 29, 2010 8:08:22 AM com.google.apphosting.utils.jetty.JettyLogger warn WARNING: Error for /users/close_users java.lang.OutOfMemoryError: Java heap space at org.jruby.RubyHash.internalPut(RubyHash.java:480) at org.jruby.RubyHash.internalPut(RubyHash.java:461) at org.jruby.RubyHash.fastASet(RubyHash.java:837) at org.jruby.RubyArray.makeHash(RubyArray.java:2998) at org.jruby.RubyArray.makeHash(RubyArray.java:2992) at org.jruby.RubyArray.op_diff(RubyArray.java:3103) at org.jruby.RubyArray$i_method_1_0$RUBYINVOKER$op_diff.call(org/jruby/RubyArray$i_method_1_0$RUBYINVOKER$op_diff.gen) at org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:146) at org.jruby.ast.CallOneArgNode.interpret(CallOneArgNode.java:57) at org.jruby.ast.LocalAsgnNode.interpret(LocalAsgnNode.java:123) at org.jruby.ast.NewlineNode.interpret(NewlineNode.java:104) at org.jruby.ast.BlockNode.interpret(BlockNode.java:71) at org.jruby.runtime.InterpretedBlock.evalBlockBody(InterpretedBlock.java:373) at org.jruby.runtime.InterpretedBlock.yield(InterpretedBlock.java:346) at org.jruby.runtime.InterpretedBlock.yield(InterpretedBlock.java:303) at org.jruby.runtime.Block.yield(Block.java:194) at org.jruby.RubyArray.collect(RubyArray.java:2354) at org.jruby.RubyArray$i_method_0_0$RUBYFRAMEDINVOKER$collect.call(org/jruby/RubyArray$i_method_0_0$RUBYFRAMEDINVOKER$collect.gen) at org.jruby.runtime.callsite.CachingCallSite.callBlock(CachingCallSite.java:115) at org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:122) at org.jruby.ast.CallNoArgBlockNode.interpret(CallNoArgBlockNode.java:64) at org.jruby.ast.CallNoArgNode.interpret(CallNoArgNode.java:61) at org.jruby.ast.LocalAsgnNode.interpret(LocalAsgnNode.java:123) at org.jruby.ast.NewlineNode.interpret(NewlineNode.java:104) at org.jruby.ast.BlockNode.interpret(BlockNode.java:71) at org.jruby.ast.EnsureNode.interpret(EnsureNode.java:98) at org.jruby.ast.BeginNode.interpret(BeginNode.java:83) at org.jruby.ast.NewlineNode.interpret(NewlineNode.java:104) at org.jruby.ast.BlockNode.interpret(BlockNode.java:71) at org.jruby.ast.EnsureNode.interpret(EnsureNode.java:96) at org.jruby.internal.runtime.methods.InterpretedMethod.call(InterpretedMethod.java:201) at org.jruby.internal.runtime.methods.DefaultMethod.call(DefaultMethod.java:183)

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  • Java - HtmlUnit - Unable to save HTML to file (in some cases)

    - by Walter White
    Hi all, I am having intermittent issues saving the response HTML in HtmlUnit. Caused by: java.io.IOException: Unable to save file:C:\ccview\PP50773_4.0_walter\TSC_hca\Applications\HCA_J2EE\HCA\target\HtmlUnitTests\single\1\com\pnc\tsc\hca\ui\test\SiteCrawler\crawlSiteAsProvider\10.SiteCrawler.crawl.html at com.pnc.tsc.hca.ui.util.GetUtil.save(GetUtil.java:128) at com.pnc.tsc.hca.ui.util.GetUtil.add(GetUtil.java:75) at com.pnc.tsc.hca.ui.util.GetUtil.click(GetUtil.java:49) at com.pnc.tsc.hca.ui.test.SiteCrawler.crawl(SiteCrawler.java:87) at com.pnc.tsc.hca.ui.test.SiteCrawler.crawl(SiteCrawler.java:61) at com.pnc.tsc.hca.ui.test.SiteCrawler.crawl(SiteCrawler.java:63) at com.pnc.tsc.hca.ui.test.SiteCrawler.crawl(SiteCrawler.java:63) at com.pnc.tsc.hca.ui.test.SiteCrawler.crawl(SiteCrawler.java:63) at com.pnc.tsc.hca.ui.test.SiteCrawler.crawl(SiteCrawler.java:54) at com.pnc.tsc.hca.ui.test.SiteCrawler.crawlSiteAsProvider(SiteCrawler.java:50) ... 15 more Caused by: java.lang.RuntimeException: java.io.IOException: The system cannot find the path specified at com.gargoylesoftware.htmlunit.html.XmlSerializer.getAttributesFor(XmlSerializer.java:165) at com.gargoylesoftware.htmlunit.html.XmlSerializer.printOpeningTag(XmlSerializer.java:126) at com.gargoylesoftware.htmlunit.html.XmlSerializer.printXml(XmlSerializer.java:83) at com.gargoylesoftware.htmlunit.html.XmlSerializer.printXml(XmlSerializer.java:93) at com.gargoylesoftware.htmlunit.html.XmlSerializer.printXml(XmlSerializer.java:93) at com.gargoylesoftware.htmlunit.html.XmlSerializer.asXml(XmlSerializer.java:73) at com.gargoylesoftware.htmlunit.html.XmlSerializer.save(XmlSerializer.java:55) at com.gargoylesoftware.htmlunit.html.HtmlPage.save(HtmlPage.java:2259) at com.pnc.tsc.hca.ui.util.GetUtil.save(GetUtil.java:126) ... 24 more Caused by: java.io.IOException: The system cannot find the path specified at java.io.WinNTFileSystem.createFileExclusively(Native Method) at java.io.File.createNewFile(File.java:883) at com.gargoylesoftware.htmlunit.html.XmlSerializer.createFile(XmlSerializer.java:216) at com.gargoylesoftware.htmlunit.html.XmlSerializer.getAttributesFor(XmlSerializer.java:160) ... 32 more Now, the parent directory exists and some other files have already been written to the directory. Looking at the filename, I don't see anything that would stand out as a red flag indicating the filename is bad. What can I do to correct this error? Thanks, Walter

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  • Java RMI timeout in callback

    - by sakra
    We are using Java RMI for communication. An RMI client passes a processing request and an object with a callback method to an RMI server. The server invokes the callback when it is done with processing. The setup is similar to the one described in RMI Callbacks. Occasionally we are getting a "read time out" exception in the server upon invoking the callback method. The callback thread stalls for about a minute before the exception is raised. java.rmi.ConnectIOException: error during JRMP connection establishment; nested exception is: java.net.SocketTimeoutException: Read timed out at sun.rmi.transport.tcp.TCPChannel.createConnection(TCPChannel.java:286) at sun.rmi.transport.tcp.TCPChannel.newConnection(TCPChannel.java:184) at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:110) at java.rmi.server.RemoteObjectInvocationHandler.invokeRemoteMethod(RemoteObjectInvocationHandler.java:178) at java.rmi.server.RemoteObjectInvocationHandler.invoke(RemoteObjectInvocationHandler.java:132) at $Proxy2.finished(Unknown Source) at com.unrisk.db.grid.GridTask.invokeCallback(com.unrisk.db.grid.GridTask:1292) at com.unrisk.db.grid.GridTask.invokeCallbacks(com.unrisk.db.grid.GridTask:1304) at com.unrisk.db.service.tasks.EquityMDTask.afterRun(com.unrisk.db.service.tasks.EquityMDTask:276) at com.unrisk.db.grid.GridTask.run(com.unrisk.db.grid.GridTask:720) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) at java.lang.Thread.run(Thread.java:619) Caused by: java.net.SocketTimeoutException: Read timed out at java.net.SocketInputStream.socketRead0(Native Method) at java.net.SocketInputStream.read(SocketInputStream.java:129) at java.io.BufferedInputStream.fill(BufferedInputStream.java:218) at java.io.BufferedInputStream.read(BufferedInputStream.java:237) at java.io.DataInputStream.readByte(DataInputStream.java:248) at sun.rmi.transport.tcp.TCPChannel.createConnection(TCPChannel.java:228) ... 12 more We are using Sun Java JDK 1.6.0_18 under Windows Server 2003 32-bit. Is it possible to work around the connection problems by tuning RMI related system properties?

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  • Java 1.5 crypto on OS X - AccessControlException

    - by bpapa
    I'm trying to do a Google App Engine project on OS X (latest and greatest). I'm using classes from javax.crypto, and I'm seeing an AccessControlException thrown when I try to initialize an instance of the Mac class. Here's the stack trace: WARNING: Nested in java.lang.ExceptionInInitializerError: java.security.AccessControlException: access denied (java.lang.RuntimePermission loadLibrary.keychain) at java.security.AccessControlContext.checkPermission(AccessControlContext.java:264) at java.security.AccessController.checkPermission(AccessController.java:427) at java.lang.SecurityManager.checkPermission(SecurityManager.java:532) at com.google.appengine.tools.development.DevAppServerFactory$CustomSecurityManager.checkPermission(DevAppServerFactory.java:76) at java.lang.SecurityManager.checkLink(SecurityManager.java:818) at java.lang.Runtime.loadLibrary0(Runtime.java:816) at java.lang.System.loadLibrary(System.java:993) at com.apple.crypto.provider.HmacCore.<clinit>(HmacCore.java:26) at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27) at java.lang.reflect.Constructor.newInstance(Constructor.java:494) at java.lang.Class.newInstance0(Class.java:350) at java.lang.Class.newInstance(Class.java:303) at java.security.Provider$Service.newInstance(Provider.java:1130) at javax.crypto.Mac.a(DashoA12275) at javax.crypto.Mac.init(DashoA12275) Any ideas on 1 - what went wrong and how fix it 2 - if it's not fixable (I know Apple has not been the best supporter of Java in recent years), what's an alternative approach?

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  • java.lang.NoClassDefFoundError in command line

    - by Graham
    Hi, I'm developing an application in Eclipse and it runs fine from within Eclipse. The problem I'm having is that when I export it to a jar file and run it from the command line I get a NoClassDefFound error for javax.mail.internet. In both my project build path and class path I have included the activation.jar and mail.jar libraries required for me to use javax.mail.internet, and like I said it works fine from within Eclipse but not when I export it to a jar. If my build path has those files and so does my class path why would this not be working? Here is the error stack: Exception in thread "AWT-EventQueue-0" java.lang.NoClassDefFoundError: javax/mai l/internet/InternetAddress at airit.com.Auxiliary.validateEmail(Auxiliary.java:29) at airit.com.MainFrame.actionPerformed(MainFrame.java:79) at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.setPressed(Unknown Source) at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Sour ce) at java.awt.Component.processMouseEvent(Unknown Source) at javax.swing.JComponent.processMouseEvent(Unknown Source) at java.awt.Component.processEvent(Unknown Source) at java.awt.Container.processEvent(Unknown Source) at java.awt.Component.dispatchEventImpl(Unknown Source) at java.awt.Container.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source) at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source) at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source) at java.awt.Container.dispatchEventImpl(Unknown Source) at java.awt.Window.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.EventQueue.dispatchEvent(Unknown Source) at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.run(Unknown Source) Caused by: java.lang.ClassNotFoundException: javax.mail.internet.InternetAddress at java.net.URLClassLoader$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) ... 27 more

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  • Netbeans platform projects - problems with wrapped jar files that have dependencies

    - by I82Much
    For starters, this question is not so much about programming in the NetBeans IDE as developing a NetBeans project (e.g. using the NetBeans Platform framework). I am attempting to use the BeanUtils library to introspect my domain models and provide the properties to display in a property sheet. Sample code: public class MyNode extends AbstractNode implements PropertyChangeListener { private static final PropertyUtilsBean bean = new PropertyUtilsBean(); // snip protected Sheet createSheet() { Sheet sheet = Sheet.createDefault(); Sheet.Set set = Sheet.createPropertiesSet(); APIObject obj = getLookup().lookup (APIObject.class); PropertyDescriptor[] descriptors = bean.getPropertyDescriptors(obj); for (PropertyDescriptor d : descriptors) { Method readMethod = d.getReadMethod(); Method writeMethod = d.getWriteMethod(); Class valueType = d.getClass(); Property p = new PropertySupport.Reflection(obj, valueType, readMethod, writeMethod); set.put(p); } sheet.put(set); return sheet; } I have created a wrapper module around commons-beanutils-1.8.3.jar, and added a dependency on the module in my module containing the above code. Everything compiles fine. When I attempt to run the program and open the property sheet view (i.e.. the above code actually gets run), I get the following error: java.lang.ClassNotFoundException: org.apache.commons.logging.LogFactory at java.net.URLClassLoader$1.run(URLClassLoader.java:200) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:188) at java.lang.ClassLoader.loadClass(ClassLoader.java:319) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:330) at java.lang.ClassLoader.loadClass(ClassLoader.java:254) at org.netbeans.ProxyClassLoader.loadClass(ProxyClassLoader.java:259) Caused: java.lang.ClassNotFoundException: org.apache.commons.logging.LogFactory starting from ModuleCL@64e48e45[org.apache.commons.beanutils] with possible defining loaders [ModuleCL@75da931b[org.netbeans.libs.commons_logging]] and declared parents [] at org.netbeans.ProxyClassLoader.loadClass(ProxyClassLoader.java:261) at java.lang.ClassLoader.loadClass(ClassLoader.java:254) at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:399) Caused: java.lang.NoClassDefFoundError: org/apache/commons/logging/LogFactory at org.apache.commons.beanutils.PropertyUtilsBean.<init>(PropertyUtilsBean.java:132) at org.myorg.myeditor.MyNode.<clinit>(MyNode.java:35) at org.myorg.myeditor.MyEditor.<init>(MyEditor.java:33) at org.myorg.myeditor.OpenEditorAction.actionPerformed(OpenEditorAction.java:13) at org.openide.awt.AlwaysEnabledAction$1.run(AlwaysEnabledAction.java:139) at org.netbeans.modules.openide.util.ActionsBridge.implPerformAction(ActionsBridge.java:83) at org.netbeans.modules.openide.util.ActionsBridge.doPerformAction(ActionsBridge.java:67) at org.openide.awt.AlwaysEnabledAction.actionPerformed(AlwaysEnabledAction.java:142) at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2028) at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2351) at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387) at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242) at javax.swing.AbstractButton.doClick(AbstractButton.java:389) at com.apple.laf.ScreenMenuItem.actionPerformed(ScreenMenuItem.java:95) at java.awt.MenuItem.processActionEvent(MenuItem.java:627) at java.awt.MenuItem.processEvent(MenuItem.java:586) at java.awt.MenuComponent.dispatchEventImpl(MenuComponent.java:317) at java.awt.MenuComponent.dispatchEvent(MenuComponent.java:305) [catch] at java.awt.EventQueue.dispatchEvent(EventQueue.java:638) at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:125) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188) at java.awt.EventDispatchThread.run(EventDispatchThread.java:122) I understand that beanutils is using the commons-logging component. I have tried adding the commons-logging component in two different ways (creating a wrapper library around the commons-logging library, and putting a dependency on the Commons Logging Integration library). Neither solves the problem. I noticed that the same problem occurs with other wrapped libraries; if they themselves have external dependencies, the ClassNotFoundExceptions propagate like mad, even if I've wrapped the jars of the libraries they require and added them as dependencies to the original wrapped library module. Pictorially: I'm at my wits end here. I noticed similar problems while googling: Is there a known bug on NB Module dependency Same issue I'm facing but when wrapping a different jar NetBeans stance on this - none of the 3 apply to me. None conclusively help me. Thank you, Nick

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  • How to use apache beanutils in a NetBeans platform project? (Error with commons-logging)

    - by I82Much
    For starters, this question is not so much about programming in the NetBeans IDE as developing a NetBeans project (e.g. using the NetBeans Platform framework). I am attempting to use the BeanUtils library to introspect my domain models and provide the properties to display in a property sheet. Sample code: public class MyNode extends AbstractNode implements PropertyChangeListener { private static final PropertyUtilsBean bean = new PropertyUtilsBean(); // snip protected Sheet createSheet() { Sheet sheet = Sheet.createDefault(); Sheet.Set set = Sheet.createPropertiesSet(); APIObject obj = getLookup().lookup (APIObject.class); PropertyDescriptor[] descriptors = bean.getPropertyDescriptors(obj); for (PropertyDescriptor d : descriptors) { Method readMethod = d.getReadMethod(); Method writeMethod = d.getWriteMethod(); Class valueType = d.getClass(); Property p = new PropertySupport.Reflection(obj, valueType, readMethod, writeMethod); set.put(p); } sheet.put(set); return sheet; } I have created a wrapper module around commons-beanutils-1.8.3.jar, and added a dependency on the module in my module containing the above code. Everything compiles fine. When I attempt to run the program and open the property sheet view (i.e.. the above code actually gets run), I get the following error: java.lang.ClassNotFoundException: org.apache.commons.logging.LogFactory at java.net.URLClassLoader$1.run(URLClassLoader.java:200) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:188) at java.lang.ClassLoader.loadClass(ClassLoader.java:319) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:330) at java.lang.ClassLoader.loadClass(ClassLoader.java:254) at org.netbeans.ProxyClassLoader.loadClass(ProxyClassLoader.java:259) Caused: java.lang.ClassNotFoundException: org.apache.commons.logging.LogFactory starting from ModuleCL@64e48e45[org.apache.commons.beanutils] with possible defining loaders [ModuleCL@75da931b[org.netbeans.libs.commons_logging]] and declared parents [] at org.netbeans.ProxyClassLoader.loadClass(ProxyClassLoader.java:261) at java.lang.ClassLoader.loadClass(ClassLoader.java:254) at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:399) Caused: java.lang.NoClassDefFoundError: org/apache/commons/logging/LogFactory at org.apache.commons.beanutils.PropertyUtilsBean.<init>(PropertyUtilsBean.java:132) at org.myorg.myeditor.MyNode.<clinit>(MyNode.java:35) at org.myorg.myeditor.MyEditor.<init>(MyEditor.java:33) at org.myorg.myeditor.OpenEditorAction.actionPerformed(OpenEditorAction.java:13) at org.openide.awt.AlwaysEnabledAction$1.run(AlwaysEnabledAction.java:139) at org.netbeans.modules.openide.util.ActionsBridge.implPerformAction(ActionsBridge.java:83) at org.netbeans.modules.openide.util.ActionsBridge.doPerformAction(ActionsBridge.java:67) at org.openide.awt.AlwaysEnabledAction.actionPerformed(AlwaysEnabledAction.java:142) at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2028) at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2351) at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387) at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242) at javax.swing.AbstractButton.doClick(AbstractButton.java:389) at com.apple.laf.ScreenMenuItem.actionPerformed(ScreenMenuItem.java:95) at java.awt.MenuItem.processActionEvent(MenuItem.java:627) at java.awt.MenuItem.processEvent(MenuItem.java:586) at java.awt.MenuComponent.dispatchEventImpl(MenuComponent.java:317) at java.awt.MenuComponent.dispatchEvent(MenuComponent.java:305) [catch] at java.awt.EventQueue.dispatchEvent(EventQueue.java:638) at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:125) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188) at java.awt.EventDispatchThread.run(EventDispatchThread.java:122) I understand that beanutils is using the commons-logging component (wish it mentioned that in the javadoc, but that's OK). I have tried adding the commons-logging component in two different ways (creating a wrapper library around the commons-logging library, and putting a dependency on the Commons Logging Integration library). Neither solves the problem. Has anyone successfully used BeanUtils in a NetBeans Platform project?

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  • What java web application framework to use?

    - by frohiky
    One of the main products of my company is an Oracle Forms (and Reports) based application, that "needs" to be re-written in another technology. Why? Users want a more rich interface experience, and we want, preferably, to reduce costs with an open source application server. For this (HUGE) project, we intend to use a java web application framework, keep these points in mind: We have: hundreds of tables on our database (the ORM must be as flexible as possible); some logic which is (and will still be) based on PL/SQL procedures/functions/packages; a lot of CRUDs (the application itself is of an considerable size); a demand to work with/generate documents and workflows; an intranet based user environment; We want: to offer a RIA interface experience; use (if possible) an open source app server; a rapid (as possible) development framework; a somewhat mature framework with a "wise" roadmap (and a considerable community support); a MVC approach combined with JS or GWT widgets (e.g. Vaadin or SmartGWT); Well, in the past weeks I've read a lot of posts, Q&As on stackoverflow, and much more: Wicket, JSF, Tapestry, Grails, GWT, Struts2, Play, Spring, Seam, Echo, .... the list goes on! I've even researched about Alfresco..! The obvious question: Which one to use? At this time, any insight, recommendation, shared experience, advice will be more then welcome!

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  • Design pattern for adding / removing elements

    - by de3
    Wikipedia's definition for Iterator pattern design: the Iterator pattern is a design pattern in which iterators are used to access the elements of an aggregate object sequentially without exposing its underlying implementation. Iterator interface in java provides the following methods hasNext() next() remove() Is there a pattern design, or a java interface for inserting / deleting elements, and getting length of the aggregate object, in addition to iterating them? I know remove() is an optional method that can be used once per call to next(), but I am implementing a circular FIFO array and need a method delete() independent of iterator's next().

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  • What Design Pattern is this?

    - by 01
    I know that everything we do in programming can be described as design pattern(even abstract method has design pattern called template method) public class Guicer extends AbstractModule { private static Injector injector = Guice.createInjector(new Guicer()); public static void setInjector(Injector injector) { Guicer.injector = injector; } public static T getInstance(Class c) { return injector.getInstance(c); } @Override protected void configure() { } } What design patterns are used in this code?

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  • Why does the Java VM process eat up more RAM then specified in -Xmx parameter?

    - by evilpenguin
    I have multiple servers running CentOS 5.4 and only one application running on Java VM. I've configured the Java VM with the following arguments: java -Xmx4500M -server -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:NewSize=1024m -Djava.net.preferIPv4Stack=true -Dcom.sun.management.jmxremote=true The machines I'm running the VM on has 6 GB RAM and no other applications running. After a while, the java process starts to hit the swap space really hard, I get this info out of the top command: 7658 root 25 0 11.7g 3.9g 4796 S 39.4 67.3 543:54.17 java On the other hand, if I connect via JConsole, it reports the Java VM has 2.6 GB used, 4.6 GB commited and 4.6 Gb max. java -version returns: java version "1.6.0_17" Java(TM) SE Runtime Environment (build 1.6.0_17-b04) Java HotSpot(TM) 64-Bit Server VM (build 14.3-b01, mixed mode) Why is the Java VM expanding so much past it's allocated heap size? And where does that memory go, if it's not reported in JConsole?

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  • Are Java's public fields just a tragic historical design flaw at this point?

    - by Avi Flax
    It seems to be Java orthodoxy at this point that one should basically never use public fields for object state. (I don't necessarily agree, but that's not relevant to my question.) Given that, would it be right to say that from where we are today, it's clear that Java's public fields were a mistake/flaw of the language design? Or is there a rational argument that they're a useful and important part of the language, even today? Thanks! Update: I know about the more elegant approaches, such as in C#, Python, Groovy, etc. I'm not directly looking for those examples. I'm really just wondering if there's still someone deep in a bunker, muttering about how wonderful public fields really are, and how the masses are all just sheep, etc. Update 2: Clearly static final public fields are the standard way to create public constants. I was referring more to using public fields for object state (even immutable state). I'm thinking that it does seem like a design flaw that one should use public fields for constants, but not for state… a language's rules should be enforced naturally, by syntax, not by guidelines.

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  • How often are design patterns used in the workplace using PHP

    - by Metropolis
    Hey everyone, I read a book awhile back called PHP Design Patterns and Practice, and ever since then I have been using design patterns whenever I think they are needed. However it just occurred to me that maybe most companies do not use design patterns very often for PHP, or at all. What I was wondering is, do most companies use design patterns to help improve code flexibility? And if so, what are the best design patterns to learn for PHP? Thanks for any help on this, Metropolis

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  • Explanation of the definition of interface inheritance as described in GoF book

    - by Geek
    I am reading the first chapter of the Gof book. Section 1.6 discusses about class vs interface inheritance: Class versus Interface Inheritance It's important to understand the difference between an object's class and its type. An object's class defines how the object is implemented.The class defines the object's internal state and the implementation of its operations.In contrast,an object's type only refers to its interface--the set of requests on which it can respond. An object can have many types, and objects of different classes can have the same type. Of course, there's a close relationship between class and type. Because a class defines the operations an object can perform, it also defines the object's type . When we say that an object is an instance of a class, we imply that the object supports the interface defined by the class. Languages like c++ and Eiffel use classes to specify both an object's type and its implementation. Smalltalk programs do not declare the types of variables; consequently,the compiler does not check that the types of objects assigned to a variable are subtypes of the variable's type. Sending a message requires checking that the class of the receiver implements the message, but it doesn't require checking that the receiver is an instance of a particular class. It's also important to understand the difference between class inheritance and interface inheritance (or subtyping). Class inheritance defines an object's implementation in terms of another object's implementation. In short, it's a mechanism for code and representation sharing. In contrast,interface inheritance(or subtyping) describes when an object can be used in place of another. I am familiar with the Java and JavaScript programming language and not really familiar with either C++ or Smalltalk or Eiffel as mentioned here. So I am trying to map the concepts discussed here to Java's way of doing classes, inheritance and interfaces. This is how I think of of these concepts in Java: In Java a class is always a blueprint for the objects it produces and what interface(as in "set of all possible requests that the object can respond to") an object of that class possess is defined during compilation stage only because the class of the object would have implemented those interfaces. The requests that an object of that class can respond to is the set of all the methods that are in the class(including those implemented for the interfaces that this class implements). My specific questions are: Am I right in saying that Java's way is more similar to C++ as described in the third paragraph. I do not understand what is meant by interface inheritance in the last paragraph. In Java interface inheritance is one interface extending from another interface. But I think the word interface has some other overloaded meaning here. Can some one provide an example in Java of what is meant by interface inheritance here so that I understand it better?

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  • JDK 8 install in ubuntu

    - by maamaa
    I'm tring to install jdk 8 for weeks, but it fails.Following are some outputs, sudo update-alternatives --config java There is only one alternative in link group java (providing /usr/bin/java): /opt/java-oracle/jdk1.8.0/bin/java Nothing to configure. which java /usr/bin/java java bash: /usr/local/java/jdk1.7.0_51/bin/java: No such file or directory ls -l /usr/bin/java /usr/bin/java -> /etc/alternatives/java ls -l /etc/alternatives/java /etc/alternatives/java -> /opt/java-oracle/jdk1.8.0/bin/java sudo update-alternatives --config javac /opt/java-oracle/jdk1.8.0/bin/javac 1 manual mode javac Error: could not find libjava.so Error: Could not find Java SE Runtime Environment. If you can please give me a help to slove this problem. Thank You

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  • Is this an acceptable UI design decision?

    - by DVK
    OK, while I'm on record as stating that StackExchange UI is pretty much one of the best websites and overall GUIs that I have ever seen as far as usability goes, there's one particular aspect of the trilogy that bugs me. For an example, head on to http://meta.stackoverflow.com . Look at the banner on top (the one that says "reminder -- it's April Fool's Day depending on your time zone!"). Personally, I feel that this is a "make the user do the figuring out work" anti-pattern (whatever it's officially called) - namely, instead of making your app smart enough to only present a certain mode of operations in the conditions when that mode is appropriate, you simply turn on the mode full on and put an explanation to the user of why the mode is on when it should not be (in this particular example, the mode is of course displaying the unicorn gravatars starting with 00:00 in the first timezone, despite the fact that some users still live in March 31st). The Great Recalc was also handled the same way - instead of proactively telling the user "your rep was changed from X to Y" the same nearly invisible banner was displayed on meta. So, the questions are: Is there such an official anti-pattern, and if so,m what the heck do i call it? Do you have any other well-known examples of such design anti-pattern? How would you fix either the SO example I made or you your own example? Is there a pattern of fixing or must it be a case-by-case solution?

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