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  • Displaying individual elements of an object in an Arraylist through a for loop?

    - by user1180888
    I'm trying to Display individual elements of an Object I have created. It is a simple Java program that allows users to add and keep track of Player Details. I'm just stumped when it comes to displaying the details after they have been added already. here is what my code looks like I can create the object and input it into the arraylist no problem using the case 2, but when I try to print it out I want to do something like System.out.println("Player Name" + myPlayersArrayList.PlayerName + "Player Position" + myPlayerArrayList.PlayerPosition + "Player Age" + "Player Age"); I know that is not correct, but I dont really know what to do, if anyone can be of any help it would be greatly appreciated. Thanks System.out.println("Welcome to the Football Player database"); System.out.print(System.getProperty("line.separator")); UserInput myFirstUserInput = new UserInput(); int selection; ArrayList<Player> myPlayersArrayList = new ArrayList<Player>(); while (true) { System.out.println("1. View The Players"); System.out.println("2. Add A Player"); System.out.println("3. Edit A Player"); System.out.println("4. Delete A Player"); System.out.println("5. Exit ") ; System.out.print(System.getProperty("line.separator")); selection = myFirstUserInput.getInt("Please select an option"); System.out.print(System.getProperty("line.separator")); switch(selection){ case 1: if (myPlayersArrayList.isEmpty()) { System.out.println("No Players Have Been Entered Yet"); System.out.print(System.getProperty("line.separator")); break;} else {for(int i = 0; i < myPlayersArrayList.size(); i++){ System.out.println(myPlayersArrayList); } break; case 2: { String playerName,playerPos; int playerAge; playerName = (myFirstUserInput.getString("Enter Player name")); playerPos = (myFirstUserInput.getString("Enter Player Position")); playerAge = (myFirstUserInput.getInt("Enter Player Age")); myPlayersArrayList.add(new Player(playerName, playerPos, playerAge)); ; break; }

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  • How might one teach OO without referencing physical real-world objects?

    - by hal10001
    I remember reading somewhere that the original concepts behind OO were to find a better architecture for handling the messaging of data between multiple systems in a way that protected the state of that data. Now that is probably a poor paraphrase, but it made me wonder if there is a way of teaching OO without the (Bike, Car, Person, etc.) object analogies, and that instead focuses on the messaging aspects. If you have articles, links, books, etc., that would be helpful.

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  • Why is it a good practice to wrap all primitives and Strings?

    - by Amogh Talpallikar
    According to Jeff Bay's Essay on Object Callisthenics, One of the practices is set to be "Wrap all primitives and Strings" Can anyone elaborate on this ? In languages where we already have wrappers for primitives like C# and Java. and In languages where Collections can have generics where you are sure of what type goes into the collection, do we need to wrap string's inside their own classes ? Does it have any other advantage ?

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  • Is it a good practice to wrap all primitives and Strings?

    - by Amogh Talpallikar
    According to Jeff Bay's Essay on Object Callisthenics, One of the practices is set to be "Wrap all primitives and Strings" Can anyone elaborate on this ? In languages where we already have wrappers for primitives like C# and Java. and In languages where Collections can have generics where you are sure of what type goes into the collection, do we need to wrap string's inside their own classes ? Does it have any other advantage ?

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  • What is the diffference between "data hiding" and "encapsulation"?

    - by john smith optional
    I'm reading "Java concurrency in practice" and there is said: "Fortunately, the same object-oriented techniques that help you write well-organized, maintainable classes - such as encapsulation and data hiding -can also help you crate thread-safe classes." The problem #1 - I never heard about data hiding and don't know what it is. The problem #2 - I always thought that encapsulation is using private vs public, and is actually the data hiding. Can you please explain what data hiding is and how it differs from encapsulation?

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  • what's the point of method overloading?

    - by David
    I am following a textbook in which I have just come across method overloading. It briefly described method overloading as: when the same method name is used with different parameters its called method overloading. From what I've learned so far in OOP is that if I want different behaviors from an object via methods, I should use different method names that best indicate the behavior, so why should I bother with method overloading in the first place?

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  • Isn't MVC anti OOP?

    - by m3th0dman
    The main idea behind OOP is to unify data and behavior in a single entity - the object. In procedural programming there is data and separately algorithms modifying the data. In the Model-View-Controller pattern the data and the logic/algorithms are placed in distinct entities, the model and the controller respectively. In an equivalent OOP approach shouldn't the model and the controller be placed in the same logical entity?

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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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  • Are UML class diagrams adequated to design javascript systems?

    - by Vandell
    Given that UML is oriented towards a more classic approach to object orientation, is it still usable in a reliable way to design javascript systems? One specific problem that I can see is that class diagrams are, in fact, a structural view of the system, and javascript is more behaviour driven, how can you deal with it? Please, keep in mind that I'm not talking abot the real world domain here, It's a model for the solution that I'm trying to achieve.

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  • What if globals make sense?

    - by Greg
    I've got a value that many objects need. For example, a financial application with different investments as objects, and most of them need the current interest rate. I was hoping to encapsulate my "financial environment" as an object, with the interest rate as a property. But, sibling objects that need that value can't get to it. So how do I share values among many objects without over-coupling my design? Obviously I'm thinking about this wrong.

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  • What is the difference between "data hiding" and "encapsulation"?

    - by Software Engeneering Learner
    I'm reading "Java concurrency in practice" and there is said: "Fortunately, the same object-oriented techniques that help you write well-organized, maintainable classes - such as encapsulation and data hiding -can also help you create thread-safe classes." The problem #1 - I never heard about data hiding and don't know what it is. The problem #2 - I always thought that encapsulation is using private vs public, and is actually the data hiding. Can you please explain what data hiding is and how it differs from encapsulation?

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  • Are UML class diagrams adequate to design javascript systems?

    - by Vandell
    Given that UML is oriented towards a more classic approach to object orientation, is it still usable in a reliable way to design javascript systems? One specific problem that I can see is that class diagrams are, in fact, a structural view of the system, and javascript is more behaviour driven, how can you deal with it? Please, keep in mind that I'm not talking abot the real world domain here, It's a model for the solution that I'm trying to achieve.

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  • How to store multiple requirements with OR and AND?

    - by Cano
    Well I'm working on a personal project that needs to check if a user has met certain requirements, and they come in a form of Requirement: [c1 OR c2] AND [d1 OR d2] Requirement: [c1 AND c2] OR [d1 AND d2] Requirement: c1 AND any dn(n can be any integer) I'm just not sure how to store these sorts of requirements, I'm thinking of using another object to hold c1,c2,d1,d2....dn and OR, but that seems like a roundabout way of doing things. Is there a better method?

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  • Class initialization issues loading java.util.LogManager in Android Dalvik VM

    - by Freddy B. Rose
    I've done changes in an Android native library and installed a new system.img file but am now getting an unrelated Error on startup. I can get past it by swallowing the error but I wanted to know if anyone can explain what the issue is. The Android implementation of Logger.java claims that it is Forcing the LogManager to be initialized since its class init code performs necessary one-time setup. But this forced initialization results in a NoClassDefFoundError. I'm thinking that it has something to do with the class not having been preloaded by Zygote yet but am not that familiar with the whole class loaders and VM business. If anyone has some insight it would be greatly appreciated. Thanks. I/Zygote ( 1253): Preloading classes... D/skia ( 1253): ------ build_power_table 1.4 D/skia ( 1253): ------ build_power_table 0.714286 W/dalvikvm( 1253): Exception Ljava/lang/StackOverflowError; thrown during Ljava/util/logging/LogManager;. W/dalvikvm( 1253): Exception Ljava/lang/NoClassDefFoundError; thrown during Ljava/security/Security;. W/dalvikvm( 1253): Exception Ljava/lang/ExceptionInInitializerError; thrown during Landroid/net/http/HttpsConnection;. E/Zygote ( 1253): Error preloading android.net.http.HttpsConnection. E/Zygote ( 1253): java.lang.ExceptionInInitializerError E/Zygote ( 1253): at java.lang.Class.classForName(Native Method) E/Zygote ( 1253): at java.lang.Class.forName(Class.java:237) E/Zygote ( 1253): at java.lang.Class.forName(Class.java:183) E/Zygote ( 1253): at com.android.internal.os.ZygoteInit.preloadClasses(ZygoteInit.java:295) E/Zygote ( 1253): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:590) E/Zygote ( 1253): at dalvik.system.NativeStart.main(Native Method) E/Zygote ( 1253): Caused by: java.lang.ExceptionInInitializerError E/Zygote ( 1253): at javax.net.ssl.KeyManagerFactory$1.run(KeyManagerFactory.java:57) E/Zygote ( 1253): at javax.net.ssl.KeyManagerFactory$1.run(KeyManagerFactory.java:56) E/Zygote ( 1253): at java.security.AccessController.doPrivilegedImpl(AccessController.java:264) E/Zygote ( 1253): at java.security.AccessController.doPrivileged(AccessController.java:84) E/Zygote ( 1253): at javax.net.ssl.KeyManagerFactory.getDefaultAlgorithm(KeyManagerFactory.java:55) E/Zygote ( 1253): at org.apache.harmony.xnet.provider.jsse.SSLParameters.(SSLParameters.java:142) E/Zygote ( 1253): at org.apache.harmony.xnet.provider.jsse.SSLContextImpl.engineInit(SSLContextImpl.java:82) E/Zygote ( 1253): at android.net.http.HttpsConnection.initializeEngine(HttpsConnection.java:101) E/Zygote ( 1253): at android.net.http.HttpsConnection.(HttpsConnection.java:65) E/Zygote ( 1253): ... 6 more E/Zygote ( 1253): Caused by: java.lang.NoClassDefFoundError: java.util.logging.LogManager E/Zygote ( 1253): at java.util.logging.Logger.initHandler(Logger.java:419) E/Zygote ( 1253): at java.util.logging.Logger.log(Logger.java:1094) E/Zygote ( 1253): at java.util.logging.Logger.warning(Logger.java:906) E/Zygote ( 1253): at org.apache.harmony.luni.util.MsgHelp.loadBundle(MsgHelp.java:61) E/Zygote ( 1253): at org.apache.harmony.luni.util.Msg.getString(Msg.java:60) E/Zygote ( 1253): at java.io.BufferedInputStream.read(BufferedInputStream.java:316) E/Zygote ( 1253): at java.io.FilterInputStream.read(FilterInputStream.java:138) E/Zygote ( 1253): at java.io.BufferedInputStream.fillbuf(BufferedInputStream.java:157) E/Zygote ( 1253): at java.io.BufferedInputStream.read(BufferedInputStream.java:243) E/Zygote ( 1253): at java.util.Properties.load(Properties.java:302) E/Zygote ( 1253): at java.security.Security$1.run(Security.java:80) E/Zygote ( 1253): at java.security.Security$1.run(Security.java:67) E/Zygote ( 1253): at java.security.AccessController.doPrivilegedImpl(AccessController.java:264) E/Zygote ( 1253): at java.security.AccessController.doPrivileged(AccessController.java:84) E/Zygote ( 1253): at java.security.Security.(Security.java:66) E/Zygote ( 1253): ... 15 more W/dalvikvm( 1253): threadid=3: thread exiting with uncaught exception (group=0x2aac6170)

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  • Class initialization issues loading java.util.logging.LogManager in Android Dalvik VM

    - by Freddy B. Rose
    I've done changes in an Android native library and installed a new system.img file but am now getting an unrelated Error on startup. I can get past it by swallowing the error but I wanted to know if anyone can explain what the issue is. The Android implementation of Logger.java claims that it is Forcing the LogManager to be initialized since its class init code performs necessary one-time setup. But this forced initialization results in a NoClassDefFoundError. I'm thinking that it has something to do with the class not having been preloaded by Zygote yet but am not that familiar with the whole class loaders and VM business. If anyone has some insight it would be greatly appreciated. Thanks. I/Zygote ( 1253): Preloading classes... D/skia ( 1253): ------ build_power_table 1.4 D/skia ( 1253): ------ build_power_table 0.714286 W/dalvikvm( 1253): Exception Ljava/lang/StackOverflowError; thrown during Ljava/util/logging/LogManager;. W/dalvikvm( 1253): Exception Ljava/lang/NoClassDefFoundError; thrown during Ljava/security/Security;. W/dalvikvm( 1253): Exception Ljava/lang/ExceptionInInitializerError; thrown during Landroid/net/http/HttpsConnection;. E/Zygote ( 1253): Error preloading android.net.http.HttpsConnection. E/Zygote ( 1253): java.lang.ExceptionInInitializerError E/Zygote ( 1253): at java.lang.Class.classForName(Native Method) E/Zygote ( 1253): at java.lang.Class.forName(Class.java:237) E/Zygote ( 1253): at java.lang.Class.forName(Class.java:183) E/Zygote ( 1253): at com.android.internal.os.ZygoteInit.preloadClasses(ZygoteInit.java:295) E/Zygote ( 1253): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:590) E/Zygote ( 1253): at dalvik.system.NativeStart.main(Native Method) E/Zygote ( 1253): Caused by: java.lang.ExceptionInInitializerError E/Zygote ( 1253): at javax.net.ssl.KeyManagerFactory$1.run(KeyManagerFactory.java:57) E/Zygote ( 1253): at javax.net.ssl.KeyManagerFactory$1.run(KeyManagerFactory.java:56) E/Zygote ( 1253): at java.security.AccessController.doPrivilegedImpl(AccessController.java:264) E/Zygote ( 1253): at java.security.AccessController.doPrivileged(AccessController.java:84) E/Zygote ( 1253): at javax.net.ssl.KeyManagerFactory.getDefaultAlgorithm(KeyManagerFactory.java:55) E/Zygote ( 1253): at org.apache.harmony.xnet.provider.jsse.SSLParameters.(SSLParameters.java:142) E/Zygote ( 1253): at org.apache.harmony.xnet.provider.jsse.SSLContextImpl.engineInit(SSLContextImpl.java:82) E/Zygote ( 1253): at android.net.http.HttpsConnection.initializeEngine(HttpsConnection.java:101) E/Zygote ( 1253): at android.net.http.HttpsConnection.(HttpsConnection.java:65) E/Zygote ( 1253): ... 6 more E/Zygote ( 1253): Caused by: java.lang.NoClassDefFoundError: java.util.logging.LogManager E/Zygote ( 1253): at java.util.logging.Logger.initHandler(Logger.java:419) E/Zygote ( 1253): at java.util.logging.Logger.log(Logger.java:1094) E/Zygote ( 1253): at java.util.logging.Logger.warning(Logger.java:906) E/Zygote ( 1253): at org.apache.harmony.luni.util.MsgHelp.loadBundle(MsgHelp.java:61) E/Zygote ( 1253): at org.apache.harmony.luni.util.Msg.getString(Msg.java:60) E/Zygote ( 1253): at java.io.BufferedInputStream.read(BufferedInputStream.java:316) E/Zygote ( 1253): at java.io.FilterInputStream.read(FilterInputStream.java:138) E/Zygote ( 1253): at java.io.BufferedInputStream.fillbuf(BufferedInputStream.java:157) E/Zygote ( 1253): at java.io.BufferedInputStream.read(BufferedInputStream.java:243) E/Zygote ( 1253): at java.util.Properties.load(Properties.java:302) E/Zygote ( 1253): at java.security.Security$1.run(Security.java:80) E/Zygote ( 1253): at java.security.Security$1.run(Security.java:67) E/Zygote ( 1253): at java.security.AccessController.doPrivilegedImpl(AccessController.java:264) E/Zygote ( 1253): at java.security.AccessController.doPrivileged(AccessController.java:84) E/Zygote ( 1253): at java.security.Security.(Security.java:66) E/Zygote ( 1253): ... 15 more W/dalvikvm( 1253): threadid=3: thread exiting with uncaught exception (group=0x2aac6170)

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  • hello-1.mod.c:14: warning: missing initializer (near initialization for '__this_module.arch.unw_sec_init')

    - by Sompom
    I am trying to write a module for an sbc1651. Since the device is ARM, this requires a cross-compile. As a start, I am trying to compile the "Hello Kernel" module found here. This compiles fine on my x86 development system, but when I try to cross-compile I get the below error. /home/developer/HelloKernel/hello-1.mod.c:14: warning: missing initializer /home/developer/HelloKernel/hello-1.mod.c:14: warning: (near initialization for '__this_module.arch.unw_sec_init') Since this is in the .mod.c file, which is autogenerated I have no idea what's going on. The mod.c file seems to be generated by the module.h file. As far as I can tell, the relevant parts are the same between my x86 system's module.h and the arm kernel header's module.h. Adding to my confusion, this problem is either not googleable (by me...) or hasn't happened to anyone before. Or I'm just doing something clueless that anyone with any sense wouldn't do. The cross-compiler I'm using was supplied by Freescale (I think). I suppose it could be a problem with the compiler. Would it be worth trying to build the toolchain myself? Obviously, since this is a warning, I could ignore it, but since it's so strange, I am worried about it, and would like to at least know the cause... Thanks very much, Sompom Here are the source files hello-1.mod.c #include <linux/module.h> #include <linux/vermagic.h> #include <linux/compiler.h> MODULE_INFO(vermagic, VERMAGIC_STRING); struct module __this_module __attribute__((section(".gnu.linkonce.this_module"))) = { .name = KBUILD_MODNAME, .init = init_module, #ifdef CONFIG_MODULE_UNLOAD .exit = cleanup_module, #endif .arch = MODULE_ARCH_INIT, }; static const struct modversion_info ____versions[] __used __attribute__((section("__versions"))) = { { 0x3972220f, "module_layout" }, { 0xefd6cf06, "__aeabi_unwind_cpp_pr0" }, { 0xea147363, "printk" }, }; static const char __module_depends[] __used __attribute__((section(".modinfo"))) = "depends="; hello-1.c (modified slightly from the given link) /* hello-1.c - The simplest kernel module. * * Copyright (C) 2001 by Peter Jay Salzman * * 08/02/2006 - Updated by Rodrigo Rubira Branco <[email protected]> */ /* Kernel Programming */ #ifndef MODULE #define MODULE #endif #ifndef LINUX #define LINUX #endif #ifndef __KERNEL__ #define __KERNEL__ #endif #include <linux/module.h> /* Needed by all modules */ #include <linux/kernel.h> /* Needed for KERN_ALERT */ static int hello_init_module(void) { printk(KERN_ALERT "Hello world 1.\n"); /* A non 0 return means init_module failed; module can't be loaded.*/ return 0; } static void hello_cleanup_module(void) { printk(KERN_ALERT "Goodbye world 1.\n"); } module_init(hello_init_module); module_exit(hello_cleanup_module); MODULE_LICENSE("GPL"); Makefile export ARCH:=arm export CCPREFIX:=/opt/freescale/usr/local/gcc-4.4.4-glibc-2.11.1-multilib-1.0/arm-fsl-linux-gnueabi/bin/arm-linux- export CROSS_COMPILE:=${CCPREFIX} TARGET := hello-1 WARN := -W -Wall -Wstrict-prototypes -Wmissing-prototypes -Wno-sign-compare -Wno-unused -Werror UNUSED_FLAGS := -std=c99 -pedantic EXTRA_CFLAGS := -O2 -DMODULE -D__KERNEL__ ${WARN} ${INCLUDE} KDIR ?= /home/developer/src/ltib-microsys/ltib/rpm/BUILD/linux-2.6.35.3 ifneq ($(KERNELRELEASE),) # kbuild part of makefile obj-m := $(TARGET).o else # normal makefile default: clean $(MAKE) -C $(KDIR) M=$$PWD .PHONY: clean clean: -rm built-in.o -rm $(TARGET).ko -rm $(TARGET).ko.unsigned -rm $(TARGET).mod.c -rm $(TARGET).mod.o -rm $(TARGET).o -rm modules.order -rm Module.symvers endif

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  • Handling null values and missing object properties in Silverlight 4

    - by PeterTweed
    Before Silverlight 4 to bind a data object to the UI and display a message associated with either a null value or if the binding path was wrong, you would need to write a Converter.  In Silverlight 4 we find the addition of the markup extensions TargetNullValue and FallbackValue that allows us to display a value when a null value is found in the bound to property and display a value when the property being bound to is not found. This post will show you how to use both markup extensions. Steps: 1. Create a new Silverlight 4 application 2. In the body of the MainPage.xaml.cs file replace the MainPage class with the following code:     public partial class MainPage : UserControl     {         public MainPage()         {             InitializeComponent();             this.Loaded += new RoutedEventHandler(MainPage_Loaded);         }           void MainPage_Loaded(object sender, RoutedEventArgs e)         {             person p = new person() { NameValue = "Peter Tweed" };             this.DataContext = p;         }     }       public class person     {         public string NameValue { get; set; }         public string TitleValue { get; set; }     } This code defines a class called person with two properties.  A new instance of the class is created, only defining the value for one of the properties and bound to the DataContext of the page. 3.  In the MainPage.xaml file copy the following XAML into the LayoutRoot grid:         <Grid.RowDefinitions>             <RowDefinition Height="60*" />             <RowDefinition Height="28*" />             <RowDefinition Height="28*" />             <RowDefinition Height="30*" />             <RowDefinition Height="154*" />         </Grid.RowDefinitions>         <Grid.ColumnDefinitions>             <ColumnDefinition Width="86*" />             <ColumnDefinition Width="314*" />         </Grid.ColumnDefinitions>         <TextBlock Grid.Row="1" Height="23" HorizontalAlignment="Left" Margin="32,0,0,0" Name="textBlock1" Text="Name Value:" VerticalAlignment="Top" />         <TextBlock Grid.Row="2" Height="23" HorizontalAlignment="Left" Margin="32,0,0,0" Name="textBlock2" Text="Title Value:" VerticalAlignment="Top" />         <TextBlock Grid.Row="3" Height="23" HorizontalAlignment="Left" Margin="32,0,0,0" Name="textBlock3" Text="Non Existant Value:" VerticalAlignment="Top" />         <TextBlock Grid.Column="1" Grid.Row="1" Height="23" HorizontalAlignment="Left" Name="textBlock4" Text="{Binding NameValue, TargetNullValue='No Name!!!!!!!'}" VerticalAlignment="Top" Margin="6,0,0,0" />         <TextBlock Grid.Column="1" Grid.Row="2" Height="23" HorizontalAlignment="Left" Name="textBlock5" Text="{Binding TitleValue, TargetNullValue='No Title!!!!!!!'}" VerticalAlignment="Top" Margin="6,0,0,0" />         <TextBlock Grid.Column="1" Grid.Row="3" Height="23" HorizontalAlignment="Left" Margin="6,0,0,0" Name="textBlock6" Text="{Binding AgeValue, FallbackValue='No such property!'}" VerticalAlignment="Top" />    This XAML defines three textblocks – two of which use the TargetNull and one that uses the FallbackValue markup extensions.  4. Run the application and see the person name displayed as defined for the person object, the expected string displayed for the TargetNullValue when no value exists for the boudn property and the expected string displayed for the FallbackValue when the property bound to is not found on the bound object. It's that easy!

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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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  • OpenGL Fast-Object Instancing Error

    - by HJ Media Studios
    I have some code that loops through a set of objects and renders instances of those objects. The list of objects that needs to be rendered is stored as a std::map, where an object of class MeshResource contains the vertices and indices with the actual data, and an object of classMeshRenderer defines the point in space the mesh is to be rendered at. My rendering code is as follows: glDisable(GL_BLEND); glEnable(GL_CULL_FACE); glDepthMask(GL_TRUE); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glEnable(GL_DEPTH_TEST); for (std::map<MeshResource*, std::vector<MeshRenderer*> >::iterator it = renderables.begin(); it != renderables.end(); it++) { it->first->setupBeforeRendering(); cout << "<"; for (unsigned long i =0; i < it->second.size(); i++) { //Pass in an identity matrix to the vertex shader- used here only for debugging purposes; the real code correctly inputs any matrix. uniformizeModelMatrix(Matrix4::IDENTITY); /** * StartHere fix rendering problem. * Ruled out: * Vertex buffers correctly. * Index buffers correctly. * Matrices correct? */ it->first->render(); } it->first->cleanupAfterRendering(); } geometryPassShader->disable(); glDepthMask(GL_FALSE); glDisable(GL_CULL_FACE); glDisable(GL_DEPTH_TEST); The function in MeshResource that handles setting up the uniforms is as follows: void MeshResource::setupBeforeRendering() { glEnableVertexAttribArray(0); glEnableVertexAttribArray(1); glEnableVertexAttribArray(2); glEnableVertexAttribArray(3); glEnableVertexAttribArray(4); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, iboID); glBindBuffer(GL_ARRAY_BUFFER, vboID); glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), 0); // Vertex position glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid*) 12); // Vertex normal glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid*) 24); // UV layer 0 glVertexAttribPointer(3, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid*) 32); // Vertex color glVertexAttribPointer(4, 1, GL_UNSIGNED_SHORT, GL_FALSE, sizeof(Vertex), (const GLvoid*) 44); //Material index } The code that renders the object is this: void MeshResource::render() { glDrawElements(GL_TRIANGLES, geometry->numIndices, GL_UNSIGNED_SHORT, 0); } And the code that cleans up is this: void MeshResource::cleanupAfterRendering() { glDisableVertexAttribArray(0); glDisableVertexAttribArray(1); glDisableVertexAttribArray(2); glDisableVertexAttribArray(3); glDisableVertexAttribArray(4); } The end result of this is that I get a black screen, although the end of my rendering pipeline after the rendering code (essentially just drawing axes and lines on the screen) works properly, so I'm fairly sure it's not an issue with the passing of uniforms. If, however, I change the code slightly so that the rendering code calls the setup immediately before rendering, like so: void MeshResource::render() { setupBeforeRendering(); glDrawElements(GL_TRIANGLES, geometry->numIndices, GL_UNSIGNED_SHORT, 0); } The program works as desired. I don't want to have to do this, though, as my aim is to set up vertex, material, etc. data once per object type and then render each instance updating only the transformation information. The uniformizeModelMatrix works as follows: void RenderManager::uniformizeModelMatrix(Matrix4 matrix) { glBindBuffer(GL_UNIFORM_BUFFER, globalMatrixUBOID); glBufferSubData(GL_UNIFORM_BUFFER, 0, sizeof(Matrix4), matrix.ptr()); glBindBuffer(GL_UNIFORM_BUFFER, 0); }

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  • Hibernate Lazy initialization exception problem with Gilead in GWT 2.0 integration

    - by sylsau
    Hello, I use GWT 2.0 as UI layer on my project. On server side, I use Hibernate. For example, this is 2 domains entities that I have : public class User { private Collection<Role> roles; @ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "users", targetEntity = Role.class) public Collection<Role> getRoles() { return roles; } ... } public class Role { private Collection<User> users; @ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, targetEntity = User.class) public Collection<User> getUsers() { return users; } ... } On my DAO layer, I use UserDAO that extends HibernateDAOSupport from Spring. UserDAO has getAll method to return all of Users. And on my DAO service, I use UserService that uses userDAO to getAll of Users. So, when I get all of Users from UsersService, Users entities returned are detached from Hibernate session. For that reason, I don't want to use getRoles() method on Users instance that I get from my service. What I want is just to transfer my list of Users thanks to a RPC Service to be able to use others informations of Users in client side with GWT. Thus, my main problem is to be able to convert PersistentBag in Users.roles in simple List to be able to transfer via RPC the Users. To do that, I have seen that Gilead Framework could be a solution. In order to use Gilead, I have changed my domains entities. Now, they extend net.sf.gilead.pojo.gwt.LightEntity and they respect JavaBean specification. On server, I expose my services via RPC thanks to GwtRpcSpring framework (http://code.google.com/p/gwtrpc-spring/). This framework has an advice that makes easier Gilead integration. My applicationContext contains the following configuration for Gilead : <bean id="gileadAdapterAdvisor" class="org.gwtrpcspring.gilead.GileadAdapterAdvice" /> <aop:config> <aop:aspect id="gileadAdapterAspect" ref="gileadAdapterAdvisor"> <aop:pointcut id="gileadPointcut" expression="execution(public * com.google.gwt.user.client.rpc.RemoteService.*(..))" /> <aop:around method="doBasicProfiling" pointcut-ref="gileadPointcut" /> </aop:aspect> </aop:config> <bean id="proxySerializer" class="net.sf.gilead.core.serialization.GwtProxySerialization" /> <bean id="proxyStore" class="net.sf.gilead.core.store.stateless.StatelessProxyStore"> <property name="proxySerializer" ref="proxySerializer" /> </bean> <bean id="persistenceUtil" class="net.sf.gilead.core.hibernate.HibernateUtil"> <property name="sessionFactory" ref="sessionFactory" /> </bean> <bean class="net.sf.gilead.core.PersistentBeanManager"> <property name="proxyStore" ref="proxyStore" /> <property name="persistenceUtil" ref="persistenceUtil" /> </bean> The code of the the method doBasicProfiling is the following : @Around("within(com.google.gwt.user.client.rpc.RemoteService..*)") public Object doBasicProfiling(ProceedingJoinPoint pjp) throws Throwable { if (log.isDebugEnabled()) { String className = pjp.getSignature().getDeclaringTypeName(); String methodName = className .substring(className.lastIndexOf(".") + 1) + "." + pjp.getSignature().getName(); log.debug("Wrapping call to " + methodName + " for PersistentBeanManager"); } GileadHelper.parseInputParameters(pjp.getArgs(), beanManager, RemoteServiceUtil.getThreadLocalSession()); Object retVal = pjp.proceed(); retVal = GileadHelper.parseReturnValue(retVal, beanManager); return retVal; } With that configuration, when I run my application and I use my RPC Service that gets all of Users, I obtain a lazy initialization exception from Hibernate from Users.roles. I am disappointed because I thought that Gilead would let me to serialize my domain entities even if these entities contained PersistentBag. It's not one of the goals of Gilead ? So, someone would know how to configure Gilead (with GwtRpcSpring or other solution) to be able to transfer domain entities without Lazy exception ? Thanks by advance for your help. Sylvain

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  • Design suggestions needed to create a MathBuilder framework

    - by Darf Zon
    Let explain what I'm trying to create. I'm creating a framework, the idea is to provide base classes to generate a math problem. Why do I need this framework? Because at first time, I realized when I create a new math problem I always do the same steps. Configuration settings such range numbers. For example if I'm developing multiplications, in beginner level only generate the first number between 2-5 or in advanced level, the first number will be between 6- 9, for example. Generate problem method. All the time I need to invoke a method like this to generate the problem. This one receives the configuration settings and generate the number according to them. And generate the object with the respective data. Validate the problem. Sometimes the problem generated is not valid. For example, supposed I'm creating fractions in most simplified, if I receive 2/4, the program should detect that this is not valid and must generate another like this one, 1/4. Load the view. All of them, have a custom view (please watch below the images). All of the problems must know how to CHECK if the user result is correct. All of this problems has answers. Some of them just require one answer, anothers may require more than one, so I guess a way to maintain flexibility to the developer has all the answers he wanna used. At the beginning I started using PRISM. Generate modules for each math problem was the idea and load it in the main system. I guess are the most important things of this idea. Let me showing some problems which I create in a WPF standalone program. Here I have a math problem about areas. When I generate the problem a set to the view the object and it draw it. In beginner level, I set in the configuration settings that just load square types. But in advance level, can load triangles and squares randomly. In this another, generate a binary problem like addition, subtraction, multiplication or division. Above just generate a single problem. The idea of this is to show a test o quiz, I mean get a worksheet (this I call as a collection of problems) where the user can answer it. I hope gets the idea with my ugly drawing. How to load this math problems? As I said above, I started using PRISM, and each module contains a math problem kind. This is a snapshot of my first demo. Below show the modules loaded, and center the respective configurations or levels. Until momment, I have no idea to start creating this software. I just know that I need a question | problem class, response class, user class. But I get lost about what properties should have to contain in it. Please give a little hand of this framework. I put much effort on this question, so if any isn't clear, let me know to clarify it.

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  • Starting to create a MathBuilder framework, help to start creating the design

    - by Darf Zon
    Let explain what I'm trying to create. I'm creating a framework, the idea is to provide base classes to generate a math problem. Why do I need this framework? Because at first time, I realized when I create a new math problem I always do the same steps. Configuration settings such range numbers. For example if I'm developing multiplications, in beginner level only generate the first number between 2-5 or in advanced level, the first number will be between 6- 9, for example. Generate problem method. All the time I need to invoke a method like this to generate the problem. This one receives the configuration settings and generate the number according to them. And generate the object with the respective data. Validate the problem. Sometimes the problem generated is not valid. For example, supposed I'm creating fractions in most simplified, if I receive 2/4, the program should detect that this is not valid and must generate another like this one, 1/4. Load the view. All of them, have a custom view (please watch below the images). All of the problems must know how to CHECK if the user result is correct. All of this problems has answers. Some of them just require one answer, anothers may require more than one, so I guess a way to maintain flexibility to the developer has all the answers he wanna used. At the beginning I started using PRISM. Generate modules for each math problem was the idea and load it in the main system. I guess are the most important things of this idea. Let me showing some problems which I create in a WPF standalone program. Here I have a math problem about areas. When I generate the problem a set to the view the object and it draw it. In beginner level, I set in the configuration settings that just load square types. But in advance level, can load triangles and squares randomly. In this another, generate a binary problem like addition, subtraction, multiplication or division. Above just generate a single problem. The idea of this is to show a test o quiz, I mean get a worksheet (this I call as a collection of problems) where the user can answer it. I hope gets the idea with my ugly drawing. How to load this math problems? As I said above, I started using PRISM, and each module contains a math problem kind. This is a snapshot of my first demo. Below show the modules loaded, and center the respective configurations or levels. Until momment, I have no idea to start creating this software. I just know that I need a question | problem class, response class, user class. But I get lost about what properties should have to contain in it. Please give a little hand of this framework. I put much effort on this question, so if any isn't clear, let me know to clarify it.

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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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  • 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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