Ryan Harrison My blog, portfolio and technology related ramblings

C# - String concatenation instead of StringBuilders

In C# when you concatenate two strings together you are implicitly creating a lot of strings in memory - more than you would have thought. For example consider the code:

  
List<string> values = new List<string>() {"foo ", "bar ","baz"};
string output = string.Empty;
foreach (var value in values)
{ 
    output += value; 
} 

Behind the scenes new strings are created for each portion of the resulting string in completely different memory locations through inefficient copy operations. So in total in this one line we have created: 1. "foo" 2. "bar" 3 "baz" 4 "foo bar" 5. "foo bar baz" In just one seemingly simple concatenation loop 5 strings have been created which of course is wildly inefficient. The problem gets a lot worse when you end up concatenating hundreds of strings together in a loop like this. The solution is to use StringBuilders. The above code is converted into:

 
List<string> values = new List<string>() {"foo ", "bar ","baz"};
StringBuilder builder = new StringBuilder();
foreach (var value in values)
{
    builder.Append(value);
} 

Using this method is a lot more efficient thanks to the fact that StringBuilders keep the same position in memory for their strings and do not perform inefficient copy operations each time a new string is appended (for example number 4 from above would not be created in a completely separate memory location). This makes StringBuilders very useful when concatenating many strings at once. But that doesn’t mean go replace all of your string concatenation code with StringBuilders right away. There are some situations where explicitly using a StringBuilder can make the situation worse. For example:

string result = "foo " + "bar " + "baz";

You might think that this suffers with the same inefficiencies as in the first example but in fact it doesn’t at all. The difference is that compile-time concatenations (which is what’s happening here) are automatically translated by the compiler into the appropriate calls to String.Concat() (which is the fastest way). Adding a StringBuilder would essentially be ruining the optimisations made by the compiler. The use of StringBuilder should be reserved to building complex strings at runtime - not replacing compile time concatenations.

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C# - Casting with (T) vs. as (T)

In C# there are two methods for casting:

  1. (T) works with both value and reference types. It casts the object to T, and throws an InvalidCastException if the cast isn’t valid.
    e.g -; Foo obj = (Foo) bar;
  2. as (T) works only with reference types. It returns the object casted to T if it succeeds, and null if the cast isn’t valid.
    e.g -;
Foo obj = bar as Foo;  
if(obj == null)
{  
  // the cast did not succeed so proceed accordingly  
}  

The question therefore is which one should be used where?

Using (T) means that you fully expect the cast to succeed. If it doesn’t succeed then there is an error in the code that needs looking at.

Using as (T) on the other hand means that you do not fully expect the cast to succeed in every case. It is considered normal behaviour if the cast did not succeed and this would be taken care of through a null check afterwards.

The only mistake is when you use as (T) but do not follow it up with a null check. The developer fully expects the cast to succeed so doesn’t write the null check. However later down the line when something goes wrong, no exception is thrown on the invalid cast, no null check is performed, and you have yourself a bug that is hard to track down. It is best to always use the regular cast (T) unless you intend to check yourself for the invalid cast via as (T) and a null check afterwards.

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CryptoLocker - Malware That Encrypts Your Data

So apparently there is a new bit of malware going around now which is particularly nasty. It encrypts all of the data on your drive and mapped network drives with an RSA 256 bit AES key. Once encrypted there is obviously no way to decrypt it again. The only way to get the files back is from an off site backup (because if the backup drive is local it also gets encrypted) or to pay them their ransom which would of course decrypt your files (not). The fact that this also attacks networked drives is particularly annoying and I bet this would catch a lot of people out if they were to get infected.

CryptoLocker Screenshot

Source and More Info

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Git Bash - Refer to files without absolute paths

When using the Git version control system with Git Bash it can often become annoying when you have to manually type in the full absolute paths to particular files in your project. For example when trying to add changes to the staging area or checking out a file, in a large project typing out the full file path can be very tedious:

git add src/uk/co/ryanharrison/snippetmanager/SnippetManager.java

or

git checkout src/uk/co/ryanharrison/snippetmanager/Snippet.java

The problem is especially bad when working on Java projects as the folder structure follows the package names which can often get rather long.

Handily there is an alternative when using Git Bash to all this typing - the ‘*’ or ‘2-asterisk globstar; which searches recursively down your file structure for a file matching the given name.

The above commands can then be replaced with:

git add **/SnippetManager.java

which will add any file called SnippetManager.java Bash finds below the current working directory to the staging area. The same works with all other commands:

git checkout **/Snippet.java

Apparently for this to work in Bash you first have to activate globstar using this command:

shopt -s globstar

however the Git Bash in Windows does not seem to support this. The functionality seems to still work though, at least when using it within Git commands.

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Android - Stocks app

I’ve written and Android app that can be used to view stocks and shares information from a wide variety of different businesses. The user maintains their own stocks portfolio so they only see the latest figures and information for the tickers that they are interested in - be it technology businesses such as Google or Microsoft, or perhaps just the popular financial indicator such as the FTSE or Dow Jones. The portfolio can be added to or removed from at the users convenience.

The full source code for this app is available on my GitHub account.

Also download the .apk file to install it on your own devices (Froyo and above).

Rather than presenting the information in a big long table, this app aims to give you the basic information about each ticker in a more graphical way. I’ve used colour coded tiles instead of a table which displays red for a ticker that has gone down in price in the current day of trading, or green if it has risen. Other pieces of the most important information is also present in each of the tiles. This includes the market the stock trades in, the current price, the price change, the price change percentage and the market capitalisation value.

Here is the main app display which shows the ticker tiles for each of the stocks currently in the users’ portfolio. As more stocks are added, tiles are added to the bottom. The figures themselves can be updated by tapping the icon in the top rightmost corner. In a way this almost replicates ‘live tiles’ in Windows 8.

Stocks Main

As I said before the tickers that are monitored on this screen can easily be added to through the use of the ‘+’ icon in the top right hand corner. This brings up the ‘Add ticker’ screen that allows you to search for a given company. In this example I search for ‘Google’ which brings up a list of possible stocks to add to the monitored portfolio. Here I choose the main Google ticker ‘GOOG’. It immediately gets added as another tile on the main screen with the most recent price information. To remove a ticker from the portfolio, hold your finger on the appropriate tile and select ‘ok’ in the confirmation menu that appears. The tile will be immediately removed from the main screen and the figures for the stock will no longer be downloaded unless the ticker is added again through the ‘Add Ticker’ view.

Stocks Add

Stocks Added

To view more detailed information and figures about a particular ticker in your portfolio, simply tap the appropriate tile that contains the relevant ticker. This brings up a new screen containing further financial figures about the stock along with a news feed with items relating to the stock. The news feed is updated constantly with the tickers to present the newest articles. Tapping a news article opens up the article in your web browser. For example here is the display for Yahoo Inc which was accessed by simply touching the Yahoo tile on the main display. As you can see the news feed is presented at the bottom and more detailed figures are at the top including the Day Highs and Low, Years High and Low and Volume figures.

Stocks Info

When inside the detailed information view for a particular stock, you can also view various charts for the stock which illustrate the price changes over a certain timeframe. Access this by tapping the ‘View Chart’ button. By default a 3 month chart will be shown however you can change the charts timespan by selecting an option from the top of the page. Here is an example showing the 1 month chart for Yahoo -

Stocks Chart

Each view in the app is fully compatible with a wide range of screen resolutions in both portrait and landscape. For example when flipped to landscape, the detailed information view for a stock is changed to present the information in a more user friendly manner -

Stocks Info Landscape

All data in the app is downloaded from the API’s by Yahoo! Finance (free for personal use). The app is also compatible with devices running Android Froyo (version 8) and above. I may do further posts on the internal infrastructure of the app which relies heavily on parsing retrieved XML and JSON data.

Get the full source code from my GitHub account.

Download the .apk file to install the app on your own devices (Froyo and above).

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