C# 4 and .NET 4

84 ❘ ChaPTer 3 Objects And types
sTaTiC Classes
Earlier, this chapter discussed static constructors and how they allowed the initialization of static member
variables. If a class contains nothing but static methods and properties, the class itself can become static. A
static class is functionally the same as creating a class with a private static constructor. An instance of the
class can never be created. By using the static keyword, the compiler can help by checking that instance
members are never accidentally added to the class. If they are, a compile error happens. This can help
guarantee that an instance is never created. The syntax for a static class looks like this:
static class StaticUtilities
{
public static void HelperMethod()
{
}
}
An object of type StaticUtilities is not needed to call the HelperMethod(). The type name is used to
make the call:
StaticUtilities.HelperMethod();
The objeCT Class
As indicated earlier, all .NET classes are ultimately derived from System.Object. In fact, if you don’t
specify a base class when you define a class, the compiler will automatically assume that it derives
from Object. Because inheritance has not been used in this chapter, every class you have seen here is
actually derived from System.Object. (As noted earlier, for structs this derivation is indirect — a struct is
always derived from System.ValueType, which in turn derives from System.Object.)
The practical significance of this is that, besides the methods and properties and so on that you define,
you also have access to a number of public and protected member methods that have been defined for the
Object class. These methods are available in all other classes that you define.
system.object methods
For the time being, we simply summarize the purpose of each method in the following list, and then, in the
next section, we provide more detail about the ToString() method in particular.
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ToString() — A fairly basic, quick-and-easy string representation, use it when you just want
a quick idea of the contents of an object, perhaps for debugging purposes. It provides very little
choice of how to format the data. For example, dates can, in principle, be expressed in a huge variety
of different formats, but DateTime.ToString() does not offer you any choice in this regard.
If you need a more sophisticated string representation that, for example, takes account of your
formatting preferences or of the culture (the locale), then you should implement the IFormattable
interface (see Chapter 9).
GetHashCode() — If objects are placed in a data structure known as a map (also known as a hash
table or dictionary), it is used by classes that manipulate these structures to determine where to
place an object in the structure. If you intend your class to be used as a key for a dictionary, you
will need to override GetHashCode(). Some fairly strict requirements exist for how you implement
your overload, and you learn about those when you examine dictionaries in Chapter 10,
“Collections.”
Equals() (both versions) and ReferenceEquals() — As you’ll gather by the existence of three different
methods aimed at comparing the equality of objects, the .NET Framework has quite a sophisticated
scheme for measuring equality. Subtle differences exist between how these three methods,
along with the comparison operator, ==, are intended to be used. Not only that, but restrictions also
exist on how you should override the virtual, one-parameter version of Equals() if you choose to do
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