patterns practices - Page 46

First 10 programs in a new scripting languge

- by pro_metedor

When a peron is learning a new scripting language like: bash python perl pike What kind of simple (yet practical) problem solutions to get through to make say that a person is comprehend with this scripting language enough to approach some complex yet still practical problems encountered in everyday job. In other words, which problems would you give that person to solve to make sure that he/she is familiar with the scripting language.

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How do you think about an Application Generator? [closed]

- by Mehdi Sheyda

I'm designing an application-generating application. It is an application that takes the requirements of customer as inputs , analyzes the requirements, creates classes and produces program files in C#. I am at the beginning of this project and have a long way to go with this application. Do you have an experience with designing similar kinds of projects? What risks might I encounter with this project?

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Is this kind of design - a class for Operations On Object - correct?

- by Mithir

In our system we have many complex operations which involve many validations and DB activities. One of the main Business functionality could have been designed better. In short, there were no separation of layers, and the code would only work from the scenario in which it was first designed at, and now there were more scenarios (like requests from an API or from other devices) So I had to redesign. I found myself moving all the DB code to objects which acts like Business to DB objects, and I've put all the business logic in an Operator kind of a class, which I've implemented like this: First, I created an object which will hold all the information needed for the operation let's call it InformationObject. Then I created an OperatorObject which will take the InformationObject as a parameter and act on it. The OperatorObject should activate different objects and validate or check for existence or any scenario in which the business logic is compromised and then make the operation according to the information on the InformationObject. So my question is - Is this kind of implementation correct? PS, this Operator only works on a single Business-wise Operation.

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Why do programmers seem to be such bad spellers?

- by Joel Etherton

Programming languages are very precise tools based on explicit grammars. They're very picky, and when being used they require an exacting amount of detail. C#, for instance, is case sensitive so even getting the case of an argument wrong will cause an error. Questions asked all over the StackExchange are replete with misspellings, grammatical errors, and other problems that seem to indicate a lack of attention to detail when it comes to the language itself. Now, I understand there are a lot of programmers out there whose native language is not English, and I am not directing this question (rant one might say) at them. I'm referring to the individuals who are clearly from an English speaking background who refuse to pay attention to these simple details. I am not perfect by any means, but I try to use the language correctly so that my meaning will be understood correctly. I find programmers misspelling variable names, classes, and all manner of words in any kind of technical documentation they might write. I have had to withstand code where I am repeatedly referring to the subit[sic] button or HttpWebResponse reponse. The general complaint about bad spelling is one thing, and it will always be there. I accept that. But my question/comment is about the proclivity of bad spelling within the programming community. I would think that people who deal with such exacting tools to be more naturally predisposed towards proper spelling. Yet this doesn't seem to be the case.

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DDD: Service or Repository

- by tikhop

I am developing an app in DDD manner. And I have a little problem with it. I have a Fare (airline fare) and FareRepository objects. And at some point I should load additional fare information and set this information to existing Fare. I guess that I need to create an Application Service (FareAdditionalInformationService) that will deal with obtaining data from the server and than update existing Fare. However, some people said me that it is necessary to use FareRepository for this problem. I don't know wich place is better for my problem Service or Repository.

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Windows Azure Database (SQL Azure) Development Tip

- by BuckWoody

When you create something in the cloud, it's real, and you're charged for it. There are free offerings, and you even get free resources with your Microsoft Developer Network (MSDN) subscription, but there are limits within those. Creating a 1 GB database - even with nothing in it - is a 1 GB Database. If you create it, drop it, and create it again 2 minutes later, that's 2 GB of space you've used for the month. Wait - how do I develop in this kind of situation? With Windows Azure, you can simply install the free Software Development Kit (SDK) and develop your entire application for free - you need never even log in to Windows Azure to code. Once you're done, you simply deploy the app and you start making money from the application as you're paying for it. Windows Azure Databases (The Artist Formerly Known As SQL Azure) is a bit different. It's not emulated in the SDK - because it doesn't have to be. It's just SQL Server, with some differences in feature set. To develop in this environment, you can use SQL Server, any edition. Be aware of the feature differences, of course, but just develop away - even in the free "Express" or LocalDB flavors - and then right-click in SQL Server Management Studio to script objects. Script the database, but change the "Advanced" selection to the Engine Type of "SQL Azure". Bing. Although most all T-SQL ports directly, one thing to keep in mind is that you need a Clustered Index on every table. Often the Primary Key (PK) is a good choice for that.

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In defense of SELECT * in production code, in some limited cases?

- by Alexander Kuznetsov

It is well known that SELECT * is not acceptable in production code, with the exception of this pattern: IF EXISTS( SELECT * We all know that whenever we see code code like this: Listing 1. "Bad" SQL SELECT Column1 , Column2 FROM ( SELECT c. * , ROW_NUMBER () OVER ( PARTITION BY Column1 ORDER BY Column2 ) AS rn FROM data.SomeTable AS c ) AS c WHERE rn < 5 we are supposed to automatically replace * with an explicit list of columns, as follows: Listing 2. "Good" SQL SELECT Column1 , Column2 FROM...(read more)

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Serial plans: Threshold / Parallel_degree_limit = 1

- by jean-pierre.dijcks

As a very short follow up on the previous post. So here is some more on getting a serial plan and why that happens Another reason - compared to the auto DOP is not on as we looked at in the earlier post - and often more prevalent to get a serial plan is if the plan simply does not take long enough to consider a parallel path. The resulting plan and note looks like this (note that this is a serial plan!): explain plan for select count(1) from sales; SELECT PLAN_TABLE_OUTPUT FROM TABLE(DBMS_XPLAN.DISPLAY()); PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- Plan hash value: 672559287 -------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Cost (%CPU)| Time | Pstart| Pstop | -------------------------------------------------------------------------------------- PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 5 (0)| 00:00:01 | | | | 1 | SORT AGGREGATE | | 1 | | | | | | 2 | PARTITION RANGE ALL| | 960 | 5 (0)| 00:00:01 | 1 | 16 | | 3 | TABLE ACCESS FULL | SALES | 960 | 5 (0)| 00:00:01 | 1 | 16 | Note ----- - automatic DOP: Computed Degree of Parallelism is 1 because of parallel threshold 14 rows selected. The parallel threshold is referring to parallel_min_time_threshold and since I did not change the default (10s) the plan is not being considered for a parallel degree computation and is therefore staying with the serial execution. Now we go into the land of crazy: Assume I do want this DOP=1 to happen, I could set the parameter in the init.ora, but to highlight it in this case I changed it on the session: alter session set parallel_degree_limit = 1; The result I get is: ERROR: ORA-02097: parameter cannot be modified because specified value is invalid ORA-00096: invalid value 1 for parameter parallel_degree_limit, must be from among CPU IO AUTO INTEGER>=2 Which of course makes perfect sense...

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Are short identifiers bad?

- by Daniel C. Sobral

Are short identifiers bad? How does identifier length correlate with code comprehension? What other factors (besides code comprehension) might be of consideration when it comes to naming identifiers? Just to try to keep the quality of the answers up, please note that there is some research on the subject already! Edit Curious that everyone either doesn't think length is relevant or tend to prefer larger identifiers, when both links I provided indicate large identifiers are harmful!

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Web Developer interview questions

- by Baba

I read an article today that listed some basic questions about web development: Describe how POST data was submitted to a server by a browser. Explain a number of HTTP status codes (except maybe 404 and 500). Explain SOLID or name a design pattern. Explain ways to improve a page load speed or user experience. The author says "if you can’t answer the questions above there are a lot of people who wouldn’t think of you as a Senior Web Developer." My questions are: How relevant are these questions in respect to real life web programming and scalability? How true is that statement? In other words, do you consider this knowledge a requirement to be considered a Senior Web Developer? I was able to answer all the questions, too easily it seemed, so I'm wondering whether it is effective to use these or similar questions to screen developers rather than asking them to write sample code.

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Improvements to Joshua Bloch's Builder Design Pattern?

- by Jason Fotinatos

Back in 2007, I read an article about Joshua Blochs take on the "builder pattern" and how it could be modified to improve the overuse of constructors and setters, especially when an object has a large number of properties, most of which are optional. A brief summary of this design pattern is articled here [http://rwhansen.blogspot.com/2007/07/theres-builder-pattern-that-joshua.html]. I liked the idea, and have been using it since. The problem with it, while it is very clean and nice to use from the client perspective, implementing it can be a pain in the bum! There are so many different places in the object where a single property is reference, and thus creating the object, and adding a new property takes a lot of time. So...I had an idea. First, an example object in Joshua Bloch's style: Josh Bloch Style: public class OptionsJoshBlochStyle { private final String option1; private final int option2; // ...other options here <<<< public String getOption1() { return option1; } public int getOption2() { return option2; } public static class Builder { private String option1; private int option2; // other options here <<<<< public Builder option1(String option1) { this.option1 = option1; return this; } public Builder option2(int option2) { this.option2 = option2; return this; } public OptionsJoshBlochStyle build() { return new OptionsJoshBlochStyle(this); } } private OptionsJoshBlochStyle(Builder builder) { this.option1 = builder.option1; this.option2 = builder.option2; // other options here <<<<<< } public static void main(String[] args) { OptionsJoshBlochStyle optionsVariation1 = new OptionsJoshBlochStyle.Builder().option1("firefox").option2(1).build(); OptionsJoshBlochStyle optionsVariation2 = new OptionsJoshBlochStyle.Builder().option1("chrome").option2(2).build(); } } Now my "improved" version: public class Options { // note that these are not final private String option1; private int option2; // ...other options here public String getOption1() { return option1; } public int getOption2() { return option2; } public static class Builder { private final Options options = new Options(); public Builder option1(String option1) { this.options.option1 = option1; return this; } public Builder option2(int option2) { this.options.option2 = option2; return this; } public Options build() { return options; } } private Options() { } public static void main(String[] args) { Options optionsVariation1 = new Options.Builder().option1("firefox").option2(1).build(); Options optionsVariation2 = new Options.Builder().option1("chrome").option2(2).build(); } } As you can see in my "improved version", there are 2 less places in which we need to add code about any addition properties (or options, in this case)! The only negative that I can see is that the instance variables of the outer class are not able to be final. But, the class is still immutable without this. Is there really any downside to this improvement in maintainability? There has to be a reason which he repeated the properties within the nested class that I'm not seeing?

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NCurses, scrolling of multiline items, "current item" pointer and "selected items"

- by mjf

I am looking for hints/ideas for the best (most effective) way on how to scroll multi-line items as well as emphasizing of the "current item" and "selected items" such as: 1 FOO ITEM 1 Foo sub-item 2 Foo sub-item 3 Foo sub-item 2 BAR ITEM 1 Bar sub-item 3 BAZ ITEM 1 Baz sub-item 2 Baz sub-item 4 RAB ITEM 5 ZZZ ITEM 1 Zzz sub-item 2 Zzz sub-item 3 Zzz sub-item 4 Zzz sub-item using NCurses (some combination of windows, sub-windows, pads, copywin? Uff! In fact, the lines could exceed the stdscr's width so that possibility to scroll left/right would be also nice - pads?)... The whole items (including the sub-items) are supposed to be emphasized as full-width window/pad areas. The "current item" (including it's set of lines) should be emphasized (i.e. using A_BOLD), selected set of items of choice (including the set of lines for each the selected item) should be emphasized in another way (i.e. using A_REVERSE). What would you choose to cope with it the most effective NCurses way? (The less redrawals/refreshes the better and terminal is supposed to have the ability to change it's size - such as XTerm running under "floating window" management.) Thank you for your ideas (or perhaps some piece of code where something similar is already solved - I was not able to find anything helpful on the Internet. I mean I am not going to copy/paste foreign code but programming NCurses properly is still somehow difficult to me). P.S.: Would you suggest to "smooth-scroll" +1/-1 screen line or rather "jump-scroll" +lines/-lines of the items? (I personally prefer the latter one.) Sincerely, -- mjf

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Highly scalable and dynamic "rule-based" applications?

- by Prof Plum

For a large enterprise app, everyone knows that being able to adjust to change is one of the most important aspects of design. I use a rule-based approach a lot of the time to deal with changing business logic, with each rule being stored in a DB. This allows for easy changes to be made without diving into nasty details. Now since C# cannot Eval("foo(bar);") this is accomplished by using formatted strings stored in rows that are then processed in JavaScript at runtime. This works fine, however, it is less than elegant, and would not be the most enjoyable for anyone else to pick up on once it becomes legacy. Is there a more elegant solution to this? When you get into thousands of rules that change fairly frequently it becomes a real bear, but this cannot be that uncommon of a problem that someone has not thought of a better way to do this. Any suggestions? Is this current method defensible? What are the alternatives? Edit: Just to clarify, this is a large enterprise app, so no matter which solution works, there will be plenty of people constantly maintaining its rules and data (around 10). Also, The data changes frequently enough to say that some sort of centralized server system is basically a must.

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Design pattern for isomorphic trees

- by Peregring-lk

I want to create a data structure to work with isomorphic tree. I don't search for a "algorithms" or methods to check if two or more trees are isomorphic each other. Just to create various trees with the same structure. Example: 2 - - - - - - - 'a' - - - - - - - 3.5 / \ / \ / \ 3 3 'f' 'y' 1.0 3.1 / \ / \ / \ 4 7 'e' 'f' 2.3 7.7 The first "layer" or tree is the "natural tree" (a tree with natural numbers), the second layer is the "character tree" and the third one is the "float tree". The data structure has a method or iterator to traverse the tree and to make diferent operations with its values. These operations could change the value of nodes, but never its structure (first I create the structure and then I configure the tree with its diferent layers). In case of that I add a new node, this would be applied to each layer. Which known design pattern fits with this description or is related with it?

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Does heavy library and snippet codes usage make you a bad programmer?

- by Henrik P.

Overall I'm in programming for about 8 years now and it seems to me that I'm relying more and more on open source libraries and snippets (damn you GitHub!) to "get the job done". I know that in time I could write me own implementation but I like to focus on the overall design. Is this normal (non cooperate environment)? Does it make you a bad programmer if "programming" is nothing more than cluing different libraries together. Feels like it. I know about "don't reinvent the wheel" but what happens when you don't invent a single wheel anymore. What's your take on this?

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What are the consequences of immutable classes with references to mutable classes?

- by glenviewjeff

I've recently begun adopting the best practice of designing my classes to be immutable per Effective Java [Bloch2008]. I have a series of interrelated questions about degrees of mutability and their consequences. I have run into situations where a (Java) class I implemented is only "internally immutable" because it uses references to other mutable classes. In this case, the class under development appears from the external environment to have state. Do any of the benefits (see below) of immutable classes hold true even by only "internally immutable" classes? Is there an accepted term for the aforementioned "internal mutability"? Wikipedia's immutable object page uses the unsourced term "deep immutability" to describe an object whose references are also immutable. Is the distinction between mutability and side-effect-ness/state important? Josh Bloch lists the following benefits of immutable classes: are simple to construct, test, and use are automatically thread-safe and have no synchronization issues do not need a copy constructor do not need an implementation of clone allow hashCode to use lazy initialization, and to cache its return value do not need to be copied defensively when used as a field make good Map keys and Set elements (these objects must not change state while in the collection) have their class invariant established once upon construction, and it never needs to be checked again always have "failure atomicity" (a term used by Joshua Bloch) : if an immutable object throws an exception, it's never left in an undesirable or indeterminate state

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Evolution of an Application: how to manage and improve core engine?

- by Phil Carter

The web application I work on has been live for a year now, but it's time for it to evolve and one of the ways in which it is evolving is into a multi-brand application - in this case several different companies using the application, different templates/content and some slight business logic changes between them. The problem I'm facing is implementing a best practice across the site where there are differences in business logic for each brand. These will mostly be very superficial, using a an alternative mailing list provider or capturing some extra data in a form. I don't want to have if(brand === x) { ... } else { ... } all over the site especially as most of what needs to be changed can be handled with extending the existing class. I've thought of several methods that could be used to instantiate the correct class, but I'm just not sure which is going to be best especially as some seem to lead to duplication of more code than should be necessary. Here's what I've considered: 1) Use a Static Loader similar to Zend_Loader which can take the class being requested, and has knowledge of the Brand and can then return the correct object. $class = App_Loader::getObject('User', $brand); 2) Factory classes. We use these in the application already for Products but we could utilise them here also to provide a transparent interface to the class. 3) Routing the page request to a specific brand controller. This however seems like it would duplicate a lot of code/logic. Is there a pattern or something else I should be considering to solve this problem? 4) How to manage a growing project that has multiple custom instances in production? Update This is a PHP application so the decisions on which class to load are made per request. There could be upwards of 100+ different 'brands' running.

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what is best book to learn optimized programming in java [closed]

- by Abhishek Simon

Possible Duplicate: Is there a canonical book for learning Java as an experienced developer? Let me elaborate a little: I used to be a C/C++ programmer where I used data structure concept like trees, queues stack etc and tried to optimize as much as possible, minimum no. of loops, variables and tried to make it efficient. It's been a couple of years that I started writing java codes, but it is simply not that efficient in terms of performance, memory intensive etc. To the point: I want to enter programming challenges using java so I need to improve my approach at things I program. So please suggest me some books that can help me learn to program better and have a chance in solving challenges in programming.

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Testing loses its effectiveness if all programmers don't use them

- by Jeff O

Let's assume you are convinced that the extra time spent unit testing has merit and improves production. Does that still hold up when everyone working on the same code doesn't use them? This question makes me wonder if fixing tests that everyone doesn't use is a waste of time. If you correct a test so the new code will pass, you're assuming the new code is correct. The person updating the test better have a firm understanding of the reasoning behind the code change and decide if the test or the new code needs to be fixed. This much inconsistency in a team when it comes to testing is probably an indication of other problems as well. There is a certain amount of risk involved that someone else on the team will alter code that is covered by testing. Is this the point where testing becomes counter-productive?

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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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Implementing MVC pattern in SWT application

- by Pradeep Simha

I am developing an SWT application (it's basically an Eclipse plugin, so I need to use SWT). Currently my design is as follows: Model: In model, I have POJOs which represents the actual fields in views. View: It is a dumb layer, it contains just UI and contains no logic (not even event handlers) Controller: It acts as a mediator b/w those two layers. Also it is responsible for creating view layer, handling events etc. Basically I have created all of the controls in view as a static like this public static Button btnLogin and in controller I have a code like this: public void createLoginView(Composite comp) { LoginFormView.createView(comp); //This createView method is in view layer ie LoginFormView LoginFormView.btnLogin.addSelectionListener(new SelectionListener() { //Code goes here }); } Similalrly I have done for other views and controls. So that in main class and other classes I am calling just createLoginView of controller. I am doing similar thing for other views. So my question, is what I am doing is correct? Is this design good? Or I should have followed any other approach. Since I am new to SWT and Eclipse plugin development (basically I am Java EE developer having 4+ years of exp). Any tips/pointers would be appreciated.

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How to teach Exception Handling for New Programmers?

- by Kanini

How do you go about teaching Exception Handling to Programmers. All other things are taught easily - Data Structures, ASP.NET, WinForms, WPF, WCF - you name it, everything can be taught easily. With Exception Handling, teaching them try-catch-finally is just the syntactic nature of Exception Handling. What should be taught however is - What part of your code do you put in the try block? What do you do in the catch block? Let me illustrate it with an example. You are working on a Windows Forms Project (a small utility) and you have designed it as below with 3 different projects. UILayer BusinessLayer DataLayer If an Exception (let us say of loading an XDocument throws an exception) is raised at DataLayer (the UILayer calls BusinessLayer which in turns calls the DataLayer), do you just do the following //In DataLayer try { XDocument xd_XmlDocument = XDocument.Load("systems.xml"); } catch(Exception ex) { throw ex; } which gets thrown again in the BusinessLayer and which is caught in UILayer where I write it to the log file? Is this how you go about Exception Handling?

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What are the downsides to using dependency injection?

- by kerry

I recently came across an interesting question on stack overflow with some interesting reponses. I like this post for three reasons. First, I am a big fan of dependency injection, it forces you to decouple your code, create cohesive interfaces, and should result in testable classes. Second, the author took the approach I usually do when trying to evaluate a technique or technology; suspend personal feelings and try to find some compelling arguments against it. Third, it proved that it is very difficult to come up with a compelling argument against dependency injection. What are the downsides to using dependency injection?

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Explaining Explain Plan Notes for Auto DOP

- by jean-pierre.dijcks

I've recently gotten some questions around "why do I not see a parallel plan" while Auto DOP is on (I think)...? It is probably worthwhile to quickly go over some of the ways to find out what Auto DOP was thinking. In general, there is no need to go tracing sessions and look under the hood. The thing to start with is to do an explain plan on your statement and to look at the parameter settings on the system. Parameter Settings to Look At First and foremost, make sure that parallel_degree_policy = AUTO. If you have that parameter set to LIMITED you will not have queuing and we will only do the auto magic if your objects are set to default parallel (so no degree specified). Next you want to look at the value of parallel_degree_limit. It is typically set to CPU, which in default settings equates to the Default DOP of the system. If you are testing Auto DOP itself and the impact it has on performance you may want to leave it at this CPU setting. If you are running concurrent statements you may want to give this some more thoughts. See here for more information. In general, do stick with either CPU or with a specific number. For now avoid the IO setting as I've seen some mixed results with that... In 11.2.0.2 you should also check that IO Calibrate has been run. Best to simply do a: SQL> select * from V$IO_CALIBRATION_STATUS; STATUS CALIBRATION_TIME ------------- ---------------------------------------------------------------- READY 04-JAN-11 10.04.13.104 AM You should see that your IO Calibrate is READY and therefore Auto DOP is ready. In any case, if you did not run the IO Calibrate step you will get the following note in the explain plan: Note ----- - automatic DOP: skipped because of IO calibrate statistics are missing One more note on calibrate_io, if you do not have asynchronous IO enabled you will see: ERROR at line 1: ORA-56708: Could not find any datafiles with asynchronous i/o capability ORA-06512: at "SYS.DBMS_RMIN", line 463 ORA-06512: at "SYS.DBMS_RESOURCE_MANAGER", line 1296 ORA-06512: at line 7 While this is changed in some fixes to the calibrate procedure, you should really consider switching asynchronous IO on for your data warehouse. Explain Plan Explanation To see the notes that are shown and explained here (and the above little snippet ) you can use a simple explain plan mechanism. There should be no need to add +parallel etc. explain plan for <statement> SELECT PLAN_TABLE_OUTPUT FROM TABLE(DBMS_XPLAN.DISPLAY()); Auto DOP The note structure displaying why Auto DOP did not work (with the exception noted above on IO Calibrate) is like this: Automatic degree of parallelism is disabled: <reason> These are the reason codes: Parameter - parallel_degree_policy = manual which will not allow Auto DOP to kick in Hint - One of the following hints are used NOPARALLEL, PARALLEL(1), PARALLEL(MANUAL) Outline - A SQL outline of an older version (before 11.2) is used SQL property restriction - The statement type does not allow for parallel processing Rule-based mode - Instead of the Cost Based Optimizer the system is using the RBO Recursive SQL statement - The statement type does not allow for parallel processing pq disabled/pdml disabled/pddl disabled - For some reason (alter session?) parallelism is disabled Limited mode but no parallel objects referenced - your parallel_degree_policy = LIMITED and no objects in the statement are decorated with the default PARALLEL degree. In most cases all objects have a specific degree in which case Auto DOP will honor that degree. Parallel Degree Limited When Auto DOP does it works you may see the cap you imposed with parallel_degree_limit showing up in the note section of the explain plan: Note ----- - automatic DOP: Computed Degree of Parallelism is 16 because of degree limit This is an obvious indication that your are being capped for this statement. There is one quite interesting one that happens when you are being capped at DOP = 1. First of you get a serial plan and the note changes slightly in that it does not indicate it is being capped (we hope to update the note at some point in time to be more specific). It right now looks like this: Note ----- - automatic DOP: Computed Degree of Parallelism is 1 Dynamic Sampling With 11.2.0.2 you will start seeing another interesting change in parallel plans, and since we are talking about the note section here, I figured we throw this in for good measure. If we deem the parallel (!) statement complex enough, we will enact dynamic sampling on your query. This happens as long as you did not change the default for dynamic sampling on the system. The note looks like this: Note ----- - dynamic sampling used for this statement (level=5)

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Command-Query-Separation and multithreading safe interfaces

- by Tobias Langner

I like the command query separation pattern (from OOSC / Eiffel - basically you either return a value or you change the state of the class - but not both). This makes reasoning about the class easier and it is easier to write exception safe classes. Now, with multi threading, I run into a major problem: the separation of the query and the command basically invalidates the result from the query as anything can happen between those 2. So my question is: how do you handle command query separation in an multi-threaded environment? Clarification example: A stack with command query separation would have the following methods: push (command) pop (command - but does not return a value) top (query - returns the value) empty (query) The problem here is - I can get empty as status, but then I can not rely on top really retrieving an element since between the call of empty and the call of top, the stack might have been emptied. Same goes for pop & top. If I get an item using top, I can not be sure that the item that I pop is the same. This can be solved using external locks - but that's not exactly what I call threadsafe design.

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