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• null pointers vs. Null Object Pattern

  - by GlenH7

  Attribution: This grew out of a related P.SE question My background is in C / C++, but I have worked a fair amount in Java and am currently coding C#. Because of my C background, checking passed and returned pointers is second-hand, but I acknowledge it biases my point of view. I recently saw mention of the Null Object Pattern where the idea is than an object is always returned. Normal case returns the expected, populated object and the error case returns empty object instead of a null pointer. The premise being that the calling function will always have some sort of object to access and therefore avoid null access memory violations. So what are the pros / cons of a null check versus using the Null Object Pattern? I can see cleaner calling code with the NOP, but I can also see where it would create hidden failures that don't otherwise get raised. I would rather have my application fail hard (aka an exception) while I'm developing it than have a silent mistake escape into the wild. Can't the Null Object Pattern have similar problems as not performing a null check? Many of the objects I have worked with hold objects or containers of their own. It seems like I would have to have a special case to guarantee all of the main object's containers had empty objects of their own. Seems like this could get ugly with multiple layers of nesting.

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• Architecture Best Practice (MVC): Repository Returns Object & Object Member Accessed Directly or Repository Returns Object Member

  - by coderabbi

  Architecturally speaking, which is the preferable approach (and why)? $validation_date = $users_repository->getUser($user_id)->validation_date; Seems to violate Law of Demeter by accessing member of object returned by method call Seems to violate Encapsulation by accessing object member directly $validation_date = $users_repository->getUserValidationDate($user_id); Seems to violate Single Responsibility Principle as $users_repository no longer just returns User objects

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• How do I fix a noisy input device (Internal Mic)? snd_hda_intel - debug included

  - by hazrpg

  As the title says, I'm having trouble with a very noisy audio input device - the internal mic or any plugged in mics. So far I've narrowed it down to an problem in ALSA since my debug info is showing a lot of "null" values. Can anyone help? Debug Info: http://www.alsa-project.org/db/?f=e0c6fb7e10624bf7691aa2b405cf0d3968e56c63 Exert from the debug: model : (null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null),(null)

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• When would you want two references to the same object?

  - by HCBPshenanigans

  In Java specifically, but likely in other languages as well; When would it be useful to have two references to the same object? Example: Dog a = new Dog(); Dob b = a; Is there a situation where this would be useful? Why would this be a preferred solution to using a whenever you want to interact with the object represented by a? Edit: Can I just say that all of your dog related examples are Delightful!

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• The Template Method Design Pattern using C# .Net

  - by nijhawan.saurabh

  First of all I'll just put this pattern in context and describe its intent as in the GOF book:   Template Method: Define the skeleton of an algorithm in an operation, deferring some steps to Subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the Algorithm's Structure.    Usage: When you are certain about the High Level steps involved in an Algorithm/Work flow you can use the Template Pattern which allows the Base Class to define the Sequence of the Steps but permits the Sub classes to alter the implementation of any/all steps.   Example in the .Net framework: The most common example is the Asp.Net Page Life Cycle. The Page Life Cycle has a few methods which are called in a sequence but we have the liberty to modify the functionality of any of the methods by overriding them.   Sample implementation of Template Method Pattern:   Let's see the class diagram first:            Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:8.0pt; mso-para-margin-left:0in; line-height:107%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-font-kerning:1.0pt; mso-ligatures:standard;}   And here goes the code:EmailBase.cs     1 using System;     2 using System.Collections.Generic;     3 using System.Linq;     4 using System.Text;     5 using System.Threading.Tasks;     6      7 namespace TemplateMethod     8 {     9     public abstract class EmailBase    10     {    11     12         public bool SendEmail()    13         {    14             if (CheckEmailAddress() == true) // Method1 in the sequence    15             {    16                 if (ValidateMessage() == true) // Method2 in the sequence    17                 {    18                     if (SendMail() == true) // Method3 in the sequence    19                     {    20                         return true;    21                     }    22                     else    23                     {    24                         return false;    25                     }    26     27                 }    28                 else    29                 {    30                     return false;    31                 }    32     33             }    34             else    35             {    36                 return false;    37     38             }    39     40     41         }    42     43         protected abstract bool CheckEmailAddress();    44         protected abstract bool ValidateMessage();    45         protected abstract bool SendMail();    46     47     48     }    49 }    50    EmailYahoo.cs      1 using System;     2 using System.Collections.Generic;     3 using System.Linq;     4 using System.Text;     5 using System.Threading.Tasks;     6      7 namespace TemplateMethod     8 {     9     public class EmailYahoo:EmailBase    10     {    11     12         protected override bool CheckEmailAddress()    13         {    14             Console.WriteLine("Checking Email Address : YahooEmail");    15             return true;    16         }    17         protected override bool ValidateMessage()    18         {    19             Console.WriteLine("Validating Email Message : YahooEmail");    20             return true;    21         }    22     23     24         protected override bool SendMail()    25         {    26             Console.WriteLine("Semding Email : YahooEmail");    27             return true;    28         }    29     30     31     }    32 }    33   EmailGoogle.cs      1 using System;     2 using System.Collections.Generic;     3 using System.Linq;     4 using System.Text;     5 using System.Threading.Tasks;     6      7 namespace TemplateMethod     8 {     9     public class EmailGoogle:EmailBase    10     {    11     12         protected override bool CheckEmailAddress()    13         {    14             Console.WriteLine("Checking Email Address : GoogleEmail");    15             return true;    16         }    17         protected override bool ValidateMessage()    18         {    19             Console.WriteLine("Validating Email Message : GoogleEmail");    20             return true;    21         }    22     23     24         protected override bool SendMail()    25         {    26             Console.WriteLine("Semding Email : GoogleEmail");    27             return true;    28         }    29     30     31     }    32 }    33   Program.cs      1 using System;     2 using System.Collections.Generic;     3 using System.Linq;     4 using System.Text;     5 using System.Threading.Tasks;     6      7 namespace TemplateMethod     8 {     9     class Program    10     {    11         static void Main(string[] args)    12         {    13             Console.WriteLine("Please choose an Email Account to send an Email:");    14             Console.WriteLine("Choose 1 for Google");    15             Console.WriteLine("Choose 2 for Yahoo");    16             string choice = Console.ReadLine();    17     18             if (choice == "1")    19             {    20                 EmailBase email = new EmailGoogle(); // Rather than newing it up here, you may use a factory to do so.    21                 email.SendEmail();    22     23             }    24             if (choice == "2")    25             {    26                 EmailBase email = new EmailYahoo(); // Rather than newing it up here, you may use a factory to do so.    27                 email.SendEmail();    28             }    29         }    30     }    31 }    32    Final Words: It's very obvious that why the Template Method Pattern is a popular pattern, everything at last revolves around Algorithms and if you are clear with the steps involved it makes real sense to delegate the duty of implementing the step's functionality to the sub classes. Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:8.0pt; mso-para-margin-left:0in; line-height:107%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-font-kerning:1.0pt; mso-ligatures:standard;}

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• Difference between null==object and object==null

  - by priyank.mp

  Hi I would like to know diff between the above comparisons? I am getting null pointer exception when I check object.getItems() == null. But if I change it to null == object.getItems(), it workes fine. I did look into this http://stackoverflow.com/questions/2938476/what-is-the-difference-between-null-object-and-objectnull-closed But I didnt get satisfactory answer.

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• Null object that is not null

  - by Guillaume

  Hello, I use 2 threads to act like a produce/consumer using double queue (http://www.codeproject.com/KB/threads/DoubleQueue.aspx). Sometimes in my 2nd thread, I get an object that is NULL but it should not be as I filled it in the first thread. I tried this: if(myObject.Data == null) { Console.WriteLine("Null Object") // <-- Breakpoint here } When I my break point hits, I can watch myObject.Data and indeed it's NULL, but when I hit F10 and then go to the next line (which is } ) myObject.Data is not NULL. I also added a lock on myObject before if .... to be sure that no one whould use this object. How is that possible and what can I do ?

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• How to safely copy an object?

  - by Prog

  This question is going to be a little long. Please bear with me. Something that happened in a project of mine made me think about how to safely copy objects. I'll present the situation I had and then ask a question. There was a class SomeClass: class SomeClass{ Thing[] things; public SomeClass(Thing[] things){ this.things = things; } // irrelevant stuff omitted public SomeClass copy(){ return new SomeClass(things); } } There was another class Processor that takes SomeClass objects, copies them (via someClassInstance.copy()), manipulates the copy's state, and returns the copy. Here it is: class Processor{ public SomeClass processObject(SomeClass object){ SomeClass copy = object.copy(); manipulateTheCopy(copy); return copy; } // irrelevant stuff omitted } I ran this, and it had bugs. I looked into these bugs, and it turned out that the manipulations Processor does on copy actually affect not only the copy, but also the original SomeClass object that was passed into processObject. I found out that it was because the original and the copy shared state - because the original passed it's field things into the copy when creating it. This made me realize that copying objects is harder than simply instantiating them with the same fields as the original. For the two objects to be completely disconnected, without any shared state, each of the fields passed to the copy also has to be copied. And if that object contains other objects - they have to be copied too. And so on. So basically, in order to be able to actually copy an object, each class in the system must have a copy() method, that also invokes copy() on all of it's fields, and so on. So for example, for copy() in SomeClass to work, it needs to look like this: public SomeClass copy(){ Thing[] copyThings = new Thing[things.length]; for(int i=0; i<things.length; i++) copyThings[i] = things[i].copy(); return new SomeClass(copyThings); } And if Thing has object fields of it's own, than it's own copy() method must be appropriate: class Thing{ Apple apple; Pencil pencil; int number; public Thing(Apple apple, Pencil pencil, int number){ this.apple = apple; this.pencil = pencil; this.number = number; } public Thing copy(){ // 'number' is a primitve. return new Thing(apple.getCopy(), pencil.getCopy(), number); } } And so on. Of course, instead of all classes having a copy() method, the copying mechanism can happen in all of the getters and the constructors of classes (unless places where it isn't suitable, for example when the field points to an external object, not to an object that 'is part' of this object). Still, that means that in order to be able to safely copy an object - most classes would have to have copying mechanisms in their getters. My question is divided into two parts: How frequently do you need to get a copy of an object? Is this a regular issue? Is the technique described common and/or reasonable? Or is there a better way to make safe copies of objects? Or is there an easier way to safely copy objects, without them sharing any state?

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• General Overview of Design Pattern Types

  Typically most software engineering design patterns fall into one of three categories in regards to types. Three types of software design patterns include: Creational Type Patterns Structural Type Patterns Behavioral Type Patterns The Creational Pattern type is geared toward defining the preferred methods for creating new instances of objects. An example of this type is the Singleton Pattern. The Singleton Pattern can be used if an application only needs one instance of a class. In addition, this singular instance also needs to be accessible across an application. The benefit of the Singleton Pattern is that you control both instantiation and access using this pattern. The Structural Pattern type is a way to describe the hierarchy of objects and classes so that they can be consolidated into a larger structure. An example of this type is the Façade Pattern.  The Façade Pattern is used to define a base interface so that all other interfaces inherit from the parent interface. This can be used to simplify a number of similar object interactions into one single standard interface. The Behavioral Pattern Type deals with communication between objects. An example of this type is the State Design Pattern. The State Design Pattern enables objects to alter functionality and processing based on the internal state of the object at a given time.

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• Identity Map Pattern and the Entity Framework

  - by nikolaosk

  This is going to be the seventh post of a series of posts regarding ASP.Net and the Entity Framework and how we can use Entity Framework to access our datastore. You can find the first one here , the second one here and the third one here , the fourth one here , the fifth one here and the sixth one here . I have a post regarding ASP.Net and EntityDataSource. You can read it here .I have 3 more posts on Profiling Entity Framework applications. You can have a look at them here , here and here . In...(read more)

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• Unity completely broken after upgrade to 12.10?

  - by NlightNFotis

  I am facing a very frustrating issue with my computer right now. I successfully upgraded to Ubuntu 12.10 this afternoon, but after the upgrade, the graphical user interface seems completely broken. To be more specific, I can not get the Unity bar to appear on the right. I have tried many things, including (but not limited to) purging and then reinstalling the fglrx drivers, apt-get install --reinstall ubuntu-desktop, apt-get install --reinstall unity, tried to remove the Xorg and Compiz configurations, checked to see if the Ubuntu Unity wall was enabled (it was) in ccsm, all to no avail. Could someone help me troubleshoot and essentially fix this issue? NOTE: This is the output when I try to enable unity via a terminal: compiz (core) - Info: Loading plugin: core compiz (core) - Info: Starting plugin: core unity-panel-service: no process found compiz (core) - Info: Loading plugin: reset compiz (core) - Error: Failed to load plugin: reset compiz (core) - Info: Loading plugin: ccp compiz (core) - Info: Starting plugin: ccp compizconfig - Info: Backend : gsettings compizconfig - Info: Integration : true compizconfig - Info: Profile : unity compiz (core) - Info: Loading plugin: composite compiz (core) - Info: Starting plugin: composite compiz (core) - Info: Loading plugin: opengl X Error of failed request: BadRequest (invalid request code or no such operation) Major opcode of failed request: 153 (GLX) Minor opcode of failed request: 19 (X_GLXQueryServerString) Serial number of failed request: 22 Current serial number in output stream: 22 compiz (core) - Info: Unity is not supported by your hardware. Enabling software rendering instead (slow). compiz (core) - Info: Starting plugin: opengl Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 compiz (core) - Error: Plugin initScreen failed: opengl compiz (core) - Error: Failed to start plugin: opengl compiz (core) - Info: Unloading plugin: opengl compiz (core) - Info: Loading plugin: decor compiz (core) - Info: Starting plugin: decor compiz (decor) - Warn: requested a pixmap type decoration when compositing isn't available compiz (decor) - Warn: requested a pixmap type decoration when compositing isn't available compiz (decor) - Warn: requested a pixmap type decoration when compositing isn't available compiz (decor) - Warn: requested a pixmap type decoration when compositing isn't available compiz (decor) - Warn: requested a pixmap type decoration when compositing isn't available compiz (decor) - Warn: requested a pixmap type decoration when compositing isn't available compiz (decor) - Warn: requested a pixmap type decoration when compositing isn't available compiz (decor) - Warn: requested a pixmap type decoration when compositing isn't available compiz (decor) - Warn: requested a pixmap type decoration when compositing isn't available compiz (decor) - Warn: requested a pixmap type decoration when compositing isn't available compiz (decor) - Warn: requested a pixmap type decoration when compositing isn't available Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 compiz (core) - Info: Loading plugin: imgpng compiz (core) - Info: Starting plugin: imgpng compiz (core) - Info: Loading plugin: vpswitch compiz (core) - Info: Starting plugin: vpswitch compiz (core) - Info: Loading plugin: resize compiz (core) - Info: Starting plugin: resize Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 compiz (core) - Info: Loading plugin: compiztoolbox compiz (core) - Info: Starting plugin: compiztoolbox compiz (core) - Error: Plugin 'opengl' not loaded. compiz (core) - Info: Loading plugin: move compiz (core) - Info: Starting plugin: move compiz (core) - Info: Loading plugin: gnomecompat compiz (core) - Info: Starting plugin: gnomecompat compiz (core) - Info: Loading plugin: mousepoll compiz (core) - Info: Starting plugin: mousepoll compiz (core) - Info: Loading plugin: wall compiz (core) - Info: Starting plugin: wall compiz (core) - Error: Plugin 'opengl' not loaded. compiz (core) - Error: Plugin init failed: wall compiz (core) - Error: Failed to start plugin: wall compiz (core) - Info: Unloading plugin: wall compiz (core) - Info: Loading plugin: regex compiz (core) - Info: Starting plugin: regex compiz (core) - Info: Loading plugin: snap compiz (core) - Info: Starting plugin: snap compiz (core) - Info: Loading plugin: unitymtgrabhandles compiz (core) - Info: Starting plugin: unitymtgrabhandles compiz (core) - Error: Plugin 'opengl' not loaded. compiz (core) - Error: Plugin init failed: unitymtgrabhandles compiz (core) - Error: Failed to start plugin: unitymtgrabhandles compiz (core) - Info: Unloading plugin: unitymtgrabhandles compiz (core) - Info: Loading plugin: place compiz (core) - Info: Starting plugin: place compiz (core) - Info: Loading plugin: grid compiz (core) - Info: Starting plugin: grid Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 compiz (core) - Info: Loading plugin: animation compiz (core) - Info: Starting plugin: animation compiz (core) - Error: Plugin 'opengl' not loaded. compiz (core) - Error: Plugin init failed: animation compiz (core) - Error: Failed to start plugin: animation compiz (core) - Info: Unloading plugin: animation compiz (core) - Info: Loading plugin: fade compiz (core) - Info: Starting plugin: fade compiz (core) - Error: Plugin 'opengl' not loaded. compiz (core) - Error: Plugin init failed: fade compiz (core) - Error: Failed to start plugin: fade compiz (core) - Info: Unloading plugin: fade compiz (core) - Info: Loading plugin: session compiz (core) - Info: Starting plugin: session compiz (core) - Info: Loading plugin: expo compiz (core) - Info: Starting plugin: expo compiz (core) - Error: Plugin 'opengl' not loaded. compiz (core) - Error: Plugin init failed: expo compiz (core) - Error: Failed to start plugin: expo compiz (core) - Info: Unloading plugin: expo compiz (core) - Info: Loading plugin: ezoom compiz (core) - Info: Starting plugin: ezoom compiz (core) - Error: Plugin 'opengl' not loaded. compiz (core) - Error: Plugin init failed: ezoom compiz (core) - Error: Failed to start plugin: ezoom compiz (core) - Info: Unloading plugin: ezoom compiz (core) - Info: Loading plugin: workarounds compiz (core) - Info: Starting plugin: workarounds compiz (core) - Error: Plugin 'opengl' not loaded. Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 compiz (core) - Info: Loading plugin: scale compiz (core) - Info: Starting plugin: scale compiz (core) - Error: Plugin 'opengl' not loaded. compiz (core) - Error: Plugin init failed: scale compiz (core) - Error: Failed to start plugin: scale compiz (core) - Info: Unloading plugin: scale Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Compiz (opengl) - Fatal: glXQueryExtensionsString is NULL for screen 0 Segmentation fault (core dumped)

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• DB Schema for ACL involving 3 subdomains

  - by blacktie24

  Hi, I am trying to design a database schema for a web app which has 3 subdomains: a) internal employees b) clients c) contractors. The users will be able to communicate with each other to some degree, and there may be some resources that overlap between them. Any thoughts about this schema? Really appreciate your time and thoughts on this. Cheers! -- -- Table structure for table locations CREATE TABLE IF NOT EXISTS locations ( id bigint(20) NOT NULL, name varchar(250) NOT NULL ) ENGINE=InnoDB DEFAULT CHARSET=latin1; -- -- Table structure for table privileges CREATE TABLE IF NOT EXISTS privileges ( id int(11) NOT NULL AUTO_INCREMENT, name varchar(255) NOT NULL, resource_id int(11) NOT NULL, PRIMARY KEY (id) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=10 ; -- -- Table structure for table resources CREATE TABLE IF NOT EXISTS resources ( id int(11) NOT NULL AUTO_INCREMENT, name varchar(255) NOT NULL, user_type enum('internal','client','expert') NOT NULL, PRIMARY KEY (id) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ; -- -- Table structure for table roles CREATE TABLE IF NOT EXISTS roles ( id int(11) NOT NULL AUTO_INCREMENT, name varchar(255) NOT NULL, type enum('position','department') NOT NULL, parent_id int(11) DEFAULT NULL, user_type enum('internal','client','expert') NOT NULL, PRIMARY KEY (id) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ; -- -- Table structure for table role_perms CREATE TABLE IF NOT EXISTS role_perms ( id int(11) NOT NULL AUTO_INCREMENT, role_id int(11) NOT NULL, privilege_id int(11) NOT NULL, mode varchar(250) NOT NULL, PRIMARY KEY (id) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=2 ; -- -- Table structure for table users CREATE TABLE IF NOT EXISTS users ( id int(10) unsigned NOT NULL AUTO_INCREMENT, email varchar(255) NOT NULL, password varchar(255) NOT NULL, salt varchar(255) NOT NULL, type enum('internal','client','expert') NOT NULL, first_name varchar(255) NOT NULL, last_name varchar(255) NOT NULL, location_id int(11) NOT NULL, phone varchar(255) NOT NULL, status enum('active','inactive') NOT NULL DEFAULT 'active', PRIMARY KEY (id) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=4 ; -- -- Table structure for table user_perms CREATE TABLE IF NOT EXISTS user_perms ( id int(11) NOT NULL AUTO_INCREMENT, user_id int(11) NOT NULL, privilege_id int(11) NOT NULL, mode varchar(250) NOT NULL, PRIMARY KEY (id) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=2 ; -- -- Table structure for table user_roles CREATE TABLE IF NOT EXISTS user_roles ( id int(11) NOT NULL, user_id int(11) NOT NULL, role_id int(11) NOT NULL ) ENGINE=InnoDB DEFAULT CHARSET=latin1;

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• Should an object know its own ID?

  - by xenoterracide

  obj.id seems fairly common and also seems to fall within the range of something an object could know about itself. I find myself asking why should my object know its own id? It doesn't seem to have a reason to have it? One of the main reason for it existing is retrieve it, and so my repositories need to know it, and thus use it for database interaction. I also once encountered a problem where I wanted to serialize an object to JSON for a RESTful API where the id did not seem to fit in the payload, but only the URI and including it in the object made that more difficult. Should an object know it's own id? why or why not?

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• Object oriented design importance

  - by user5507

  I started studying Object Oriented Design and Modelling using the this book by James Rumbaugh. It uses a tool called Object Modeling Technique (OMT). I have certain newbie questions. I searched the net, but couldn't get answers The book is pretty old. Don't know why the school told me to learn this. I know OMT is a predecessor of the Unified Modeling Language (UML). So its a waste? Whether the concepts change very much when we move from OMT to UML? I know OMT has Object, Dynamic and Functional Model. Wikipedia says UML is compatible with OMT and UML is a model too. As per wikipedia the UML models are Static and Dynamic and they are represented by different diagrams like class, object, activity, sequence..... I couldn't find the equivalence of this in OMT. I read that there are many object oriented development methods like OMT, Booch,.... Which one is used by Industry ? Where could I get a comparison of different Object oriented development methods?

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• Liskov substitution and abstract classes / strategy pattern

  - by Kolyunya

  I'm trying to follow LSP in practical programming. And I wonder if different constructors of subclasses violate it. It would be great to hear an explanation instead of just yes/no. Thanks much! P.S. If the answer is no, how do I make different strategies with different input without violating LSP? class IStrategy { public: virtual void use() = 0; }; class FooStrategy : public IStrategy { public: FooStrategy(A a, B b) { c = /* some operations with a, b */ } virtual void use() { std::cout << c; } private: C c; }; class BarStrategy : public IStrategy { public: BarStrategy(D d, E e) { f = /* some operations with d, e */ } virtual void use() { std::cout << f; } private: F f; };

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• Listing both null and not null in mysql query

  - by tomasz

  Let's say I have the table NAME | ID | REF foo1 | 1 | NULL foo2 | 2 | 1234 foo2 | 3 | 567 foo1 | 4 | NULL foo3 | 5 | 89 I'd like to count all instances of NULL and NOT NULL in one query so that I can say NAME | null | not null foo1 | 0 | 2 foo2 | 2 | 0 foo3 | 0 | 1 I could run these two queries select NAME,count(*) from TABLE where REF is not null select NAME,count(*) from TABLE where REF is null But I'm sure there must be a simple way to do it in one mysql query.

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• What are the advantages of the delegate pattern over the observer pattern?

  - by JoJo

  In the delegate pattern, only one object can directly listen to another object's events. In the observer pattern, any number of objects can listen to a particular object's events. When designing a class that needs to notify other object(s) of events, why would you ever use the delegate pattern over the observer pattern? I see the observer pattern as more flexible. You may only have one observer now, but a future design may require multiple observers.

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• Taking Object Oriented development to the next level

  - by Songo

  Can you mention some advanced OO topics or concepts that one should be aware of? I have been a developer for 2 years now and currently aiming for a certain company that requires a web developer with a minimum experience of 3 years. I imagine the interview will have the basic object oriented topics like (Abstraction, Polymorphism, Inheritance, Design patterns, UML, Databases and ORMs, SOLID principles, DRY principle, ...etc) I have these topics covered, but what I'm looking forward to is bringing up topics such as Efferent Coupling, Afferent Coupling, Instability, The law of Demeter, ...etc. Till few days ago I never knew such concepts existed (maybe because I'm a communication engineer basically not a CS graduate.) Can you please recommend some more advanced topics concerning object oriented programming?

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• Is it better to return NULL or empty values from functions/methods where the return value is not present?

  - by P B

  I am looking for a recommendation here. I am struggling with whether it is better to return NULL or an empty value from a method when the return value is not present or cannot be determined. Take the following two methods as an examples: string ReverseString(string stringToReverse) // takes a string and reverses it. Person FindPerson(int personID) // finds a Person with a matching personID. In ReverseString(), I would say return an empty string because the return type is string, so the caller is expecting that. Also, this way, the caller would not have to check to see if a NULL was returned. In FindPerson(), returning NULL seems like a better fit. Regardless of whether or not NULL or an empty Person Object (new Person()) is returned the caller is going to have to check to see if the Person Object is NULL or empty before doing anything to it (like calling UpdateName()). So why not just return NULL here and then the caller only has to check for NULL. Does anyone else struggle with this? Any help or insight is appreciated.

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• Null check error message as "is null" or "was null"

  - by Timo Westkämper

  When doing null checks in Java code, and you throw IllegalArgumentExceptions for null values, what kind of message template do you use? We tend to use something like this public User getUser(String username){ if (username == null){ throw new IllegalArgumentException("username is null"); } // ... } What is better : "is null" or "was null", and why? For me "is null" feels more natural.

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• Building a control-flow graph from an AST with a visitor pattern using Java

  - by omegatai

  Hi guys, I'm trying to figure out how to implement my LEParserCfgVisitor class as to build a control-flow graph from an Abstract-Syntax-Tree already generated with JavaCC. I know there are tools that already exist, but I'm trying to do it in preparation for my Compilers final. I know I need to have a data structure that keeps the graph in memory, and I want to be able to keep attributes like IN, OUT, GEN, KILL in each node as to be able to do a control-flow analysis later on. My main problem is that I haven't figured out how to connect the different blocks together, as to have the right edge between each blocks depending on their nature: branch, loops, etc. In other words, I haven't found an explicit algorithm that could help me build my visitor. Here is my empty Visitor. You can see it works on basic langage expressions, like if, while and basic operations (+,-,x,^,...) public class LEParserCfgVisitor implements LEParserVisitor { public Object visit(SimpleNode node, Object data) { return data; } public Object visit(ASTProgram node, Object data) { data = node.childrenAccept(this, data); return data; } public Object visit(ASTBlock node, Object data) { } public Object visit(ASTStmt node, Object data) { } public Object visit(ASTAssignStmt node, Object data) { } public Object visit(ASTIOStmt node, Object data) { } public Object visit(ASTIfStmt node, Object data) { } public Object visit(ASTWhileStmt node, Object data) { } public Object visit(ASTExpr node, Object data) { } public Object visit(ASTAddExpr node, Object data) { } public Object visit(ASTFactExpr node, Object data) { } public Object visit(ASTMultExpr node, Object data) { } public Object visit(ASTPowerExpr node, Object data) { } public Object visit(ASTUnaryExpr node, Object data) { } public Object visit(ASTBasicExpr node, Object data) { } public Object visit(ASTFctExpr node, Object data) { } public Object visit(ASTRealValue node, Object data) { } public Object visit(ASTIntValue node, Object data) { } public Object visit(ASTIdentifier node, Object data) { } } Can anyone give me a hand? Thanks!

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• So which null equals this null, that null? maybe this null, or is it this null?

  - by GrumpyOldDBA

  Tuning takes many routes and I get into some interesting situations and often make some exciting finds, see http://sqlblogcasts.com/blogs/grumpyolddba/archive/2010/05/17/just-when-you-thought-it-was-safe.aspx for an example. Today I encountered a multitude of Foreign Key constraints on a table, now FKs are often candidates for indexes and as none of the defined keys had an index it required a closer look. I view foreign key constraints as somewhat of a pain, excessive keys can cause excessive related...(read more)

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• How to use the client object model with SharePoint2010

  - by ybbest

  In SharePoint2010, you can use client object model to communicate with SharePoint server. Today, I’d like to show you how to achieve this by using the c# console application. You can download the solution here. 1. Create a Console application in visual studio and add the following references to the project. 2. Insert your code as below ClientContext context = new ClientContext("http://demo2010a"); Web currentWeb = context.Web; context.Load(currentWeb, web =&gt; web.Title); context.ExecuteQuery(); Console.WriteLine(currentWeb.Title); Console.ReadLine(); 3. Run your code then you will get the web title displayed as shown below Note: If you got the following errors, you need to change your target framework from .Net Framework 4 client profile to .Net Framework 4 as shown below: Change from TO

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• Object behaviour or separate class?

  - by Andrew Stephens

  When it comes to OO database access you see two common approaches - the first is to provide a class (say "Customer") with methods such as Retrieve(), Update(), Delete(), etc. The other is to keep the Customer class fairly lightweight (essentially just properties) and perform the database access elsewhere, e.g. using a repository. This choice of approaches doesn't just apply to database access, it can crop up in many different OOD scenarios. So I was wondering if one way is preferable over the other (although I suspect the answer will be "it depends")! Another dev on our team argues that to be truly OO the class should be "self-contained", i.e. providing all the methods necessary to manipulate and interact with that object. I personally prefer the repository approach - I don't like bloating the Customer class with all that functionality, and I feel it results in cleaner code having it elsewhere, but I can't help thinking I'm seriously violating core OO concepts! And what about memory implications? If I retrieve thousands of Customer objects I'm assuming those with the data access methods will take up a lot more memory than the property-only objects?

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• Any enlightenment for understanding Object Oriented Programming? [closed]

  - by ????

  I studied computer science near the end of 1980s, and wasn't taught OOP that formally. With Pascal or C, when I understand the top-down design of functions, and the idea of black box, then everything just seem to make sense, as if there is a "oh I get it!" -- some kind of totally getting it and enlightenment feeling. But with OOP, all I know was the mechanics: the class, instance, method, inheritance, polymorphism, encapsulation. It was like, I knew all the "this is how it is", but never had the feeling of "I totally get it", the enlightened feeling. Would somebody be able to describe it, or point to a chapter in some book or paper which talks about OOP so that the reader can feel: "I totally get it!" on OOP?

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