You
might want to create a version of the Time
class
that is responsible for providing public static values representing
the current time and date. Example 4-12 illustrates a
simple approach to this problem.
Example 4-12. Using static public constants
public class RightNow
{
static RightNow( )
{
System.DateTime dt = System.DateTime.Now;
Year = dt.Year;
Month = dt.Month;
Date = dt.Day;
Hour = dt.Hour;
Minute = dt.Minute;
Second = dt.Second;
}
// private member variables
public static int Year;
public static int Month;
public static int Date;
public static int Hour;
public static int Minute;
public static int Second;
}
public class Tester
{
static void Main( )
{
System.Console.WriteLine ("This year: {0}",
RightNow.Year.ToString( ));
RightNow.Year = 2002;
System.Console.WriteLine ("This year: {0}",
RightNow.Year.ToString( ));
}
}
Output:
This year: 2000
This year: 2002
This works well enough, until someone comes along and changes one of
these values. As the example shows, the
RightNow.Year
value can be changed, for example,
to 2002
. This is clearly not what we’d like.
We’d like to mark the static values as constant, but that is
not possible because we don’t initialize them until the static
constructor is executed. C# provides the keyword
readonly
for exactly this
purpose. If you change the class member variable declarations as
follows:
public static readonly int Year; public static readonly int Month; public static readonly int Date; public static readonly int Hour; public static readonly int Minute; public static readonly int Second;
then comment out the reassignment in Main( )
:
// RightNow.Year = 2002; // error!
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