#1,105 – Re-Declaring a Class-Level Variable within a Method
May 28, 2014 4 Comments
You can re-declare a class-level variable within a method, that is–declare a local variable having the same name as a class-level variable. Within the scope of the method, the local variable will hide the class-level variable.
public class MyClass
{
public int x = 10;
public void MethodA()
{
double x = 4.2;
Console.WriteLine(x);
}
}
You cannot, however, reference a class-level variable before declaring the local variable, since this is interpreted as referencing the local variable before it is defined.
public void MethodA()
{
// ERROR: Can't use local variable before it's declared
Console.WriteLine(x);
double x = 4.2;
Console.WriteLine(x);
}
You also can’t reference the class-level variable in an outer scope.
public void MethodA()
{
Console.WriteLine(x);
if (DateTime.Now.DayOfWeek == DayOfWeek.Tuesday)
{
// ERROR: Can't declare local variable within this scope
double x = 4.2;
Console.WriteLine(x);
}
}
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Hi,
Not sure if this is something you plan on covering in on a future day, but you can reference the class level variable by prefixing it with “this”, in your example it would be
// ERROR: Can’t use local variable before it’s declared, unless you prefix it with this
Console.WriteLine(this.x);
Though this is ugly, and why there are people who prefix class level variables with an underscore to prevent method / class variables conflicting, particularly when initialising from the constructor.
Cheers,
Peter
Nice job Peter, thank you.
Wrong on your second example. If x is a field of the class, Console.WriteLine(x); is OK because x is the reference variable instead of local variable.
public class MyClass
{
public int x = 10;
public void MethodA()
{
// ERROR: Can’t use local variable before it’s declared
Console.WriteLine(x);
double x = 4.2;
Console.WriteLine(x);
}
}