ASP.NET PDF Viewer using C#, VB/NET

NET library components that use side effects heavily, such as GUI libraries and I/O libraries When initializing complex data structures When using inherently imperative, efficient data structures such as hash tables and hash sets When locally optimizing routines in a way that improves on the performance of the functional version of the routine When working with very large data structures or in scenarios where the allocation of data structures must be minimized for performance reasons.

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Although PL/SQL is a great language, like any language it can be misused. In this section, we ll look at two particularly common scenarios where PL/SQL can be used in a counterproductive manner.

To address the issue of integrity, it is common to make use of hash codes. In a nutshell, a hash code is a numerical value that is tied to a fixed input. One interesting aspect of hash code values is the fact that they provide a form of one-way encryption, given that the generated numeric value contains no trace of the original message data. For example, in the previous section, we examined how a strongly named assembly is assigned a digital signature based (in part) on a hash code value obtained from the assembly contents. Clearly a numerical value such as 79BB0DA9D45C6AE29F8 has no trace of the original assembly contents (types, methods, etc). To further illustrate the nature of hash codes, consider the method System.Object.GetHashCode. This virtual method may be overridden by derived types to generate a hash value based on its internal state data. The System.String class has overridden this method to return a unique hash value for the current character data. Thus, if you have two identical strings (in the same case), System.String.GetHashCode will return the same value. If even one character differs by case or content, you receive a unique numerical value. Ponder the following class definition: class Program { static void Main(string[] args) { Console.WriteLine("***** Fun with Hash Codes *****"); Console.WriteLine("Hash of 'Hello': {0}", "Hello".GetHashCode()); Console.WriteLine("Hash of 'Hello': {0}", "Hello".GetHashCode()); Console.WriteLine("Hash of 'HellO': {0}", "HellO".GetHashCode()); Console.ReadLine(); } } Notice that the first two string objects have identical content and case, while the final string has a capitalized letter O. Now ponder the output (see Figure 5-5).

SQL must be one of the most underrated and underused tools available to Java programmers in the Oracle database. Most JDBC programmers know how to write simple select, update, delete, and insert statements in Oracle. SQL is much more than that. Over the years and over

Some F# programmers don t use any imperative techniques at all except as part of the external wrapper for their programs. Adopting this form of pure functional programming for a time is an excellent way to hone your functional programming techniques.

Figure 5-5. Hash codes are unique based on their input. Of course, when you re interested in generating hash codes for large blocks of data or sensitive user information, you won t leverage GetHashCode. Truth be told, overriding this virtual method is only useful when you re designing types that may be placed in a Hashtable collection. Luckily, the .NET platform ships with types that provide implementations of many wellknown hash code algorithms. Each type is capable of operating on different input blocks and may differ based on the size of the message data and/or the size of the generated hash code. Table 5-2 documents your choices. Table 5-2. The .NET Hashing Algorithms

different versions, Oracle has expanded the capabilities of its SQL engine tremendously For example, analytic functions are a tremendously powerful feature Since the power of SQL is not understood by many JDBC programmers, it is unfortunately a standard practice to code in PL/SQL what can be done in SQL Almost always, the equivalent code in SQL will outperform that written in PL/SQL A common example is avoidable row-byrow processing This happens when, instead of writing a single SQL statement, people write a loop, fetch each record one by one, and process the record In many cases, the entire loop can and should be replaced by a single SQL statement Say we want to copy data from one table to another Let s first create the schema for this example.