Class in C#.NET

Draw UPC-A in C#.NET Class

CaseInsensitiveComparer CaseInsensitiveHashCodeProvider CollectionBase Comparer DictionaryBase Hashtable Queue ReadOnlyCollectionBase SortedList

Stack Table 4-4

Implements the IList interface using an array whose size is dynamically increased as required Manages a compact array of bit values, which are represented as Booleans, where true indicates that the bit is on (1), and false indicates the bit is off (0) Compares two objects for equivalence, ignoring the case of strings Supplies a hash code for an object, using a hashing algorithm that ignores the case of strings Provides the abstract base class for a strongly typed collection Compares two objects for equivalence, where string comparisons are case-sensitive Provides the abstract base class for a strongly typed collection of key-and-value pairs Represents a collection of key-and-value pairs that are organized based on the hash code of the key Represents a first-in, first-out collection of objects Provides the abstract base class for a strongly typed read-only collection Represents a collection of key-and-value pairs that are sorted by the keys and are accessible by key and by index Represents a simple last-in, first-out collection of objects

The following example illustrates the use of the SortedList class to store string objects:

using System; using SystemCollections; public class ExampleSortedList { public static void Main() { // Creates and initializes a new SortedList SortedList slOne = new SortedList(); slOneAdd("First", "Hello"); slOneAdd("Second", "World"); slOneAdd("Third", "!"); // Displays the properties and values of the SortedList ConsoleWriteLine( "slOne" ); ConsoleWriteLine( " Count: {0}", slOneCount ); ConsoleWriteLine( " Capacity: {0}", slOneCapacity ); ConsoleWriteLine( " Keys and Values:" ); WriteKeysAndValues( slOne ); } public static void WriteKeysAndValues( SortedList sList ) { ConsoleWriteLine( "\t-KEY-\t-VALUE-" ); for ( int i = 0; i < sListCount; i++ ) { ConsoleWriteLine( "\t{0}:\t{1}", sListGetKey(i), sListGetByIndex(i) ); } ConsoleWriteLine(); } }

The output from the preceding example code is as follows:

slOne Count: 3 Capacity: 16 Keys and Values: -KEY-VALUEFirst: Hello Second: World Third: !

If you consider any application, you can probably think of a number of things that can go wrong with it Suppose you ask the user to enter a number into your program, and then you store that number in an integer variable it s possible that the user will give you a number that exceeds the boundaries of the integer type Another possibility is that a user gives your program a filename to work with, and when the program looks for the

file, it can t be found These types of errors are unavoidable; they happen frequently and must be dealt with properly Note that we are not talking about errors that can and should be avoided You don t want to write complicated exception handling for an error such as division by zero, which you shouldn t let happen Along the same lines, there is no point in handling an error that occurs because your program tried to add an element to an array beyond the array boundaries These are program bugs, and they should be fixed before the program is considered complete Don t make the mistake of creating error-handling routines for these kinds of errors An exception handler is a piece of code that handles the first kind of error those that cannot be avoided When a program is asked to look for a file that is not there, the program code that looks for files causes an exception object to be thrown This means that it creates an object (in this case, an object of type FileNotFoundException) and then searches for code that will deal with the error If it doesn t find the code in the current method, program execution returns to the caller of the method and searches there This search continues (in a process called unwinding the call stack) until either the error is handled or the Main() method is entered If the error flows back through all the calling methods and is not handled anywhere (including in Main()), the error is caught by the NET runtime This is not good news, since it means that the user of your program will be presented with a dialog box that essentially says your program bombed out By using the techniques described in this chapter for handling errors, you will achieve the following: Take advantage of an OO approach One of the goals of OOP is to have loosely coupled objects, meaning that one object should not rely heavily on another object By decoupling the logic of the program from the logic of error handling, you will achieve good OO design Make use of an object to describe or explain an error You can create your own exception objects from class files that you build These objects can have properties that describe the error and methods that will display meaningful messages Eliminate duplicate code Very often, we must code the same thing over and over again, in order to achieve proper error handling By placing all of the code in a single object, we are able to write once, use many times, another OOP goal PART I