Experience C # Lean replacement principles 10.6.24

We know that generics can store a parent class of the class type, so we can add its subclass. Many people may have questions about this. In principle, the subclass object can be assigned to the parent class object, that is, the subclass can completely replace the place where the parent class appears, but in turn the parent class object does not replace the subclass object. We call this feature LSP ).

There are two key words in the lee's replacement principle: Is and

1. Is is used to check whether the object is compatible with the given object type,

Using system;
Using system. Collections. Generic;
Using system. LINQ;
Using system. text;

Namespace istext
{
Class Program
{
Static void main (string [] ARGs)
{
Int I = 3;
String STR = "Hello World ";
If (I is string)
{
Console. writeline ("is a given type ");
}
Else
{
Console. Write ("not a given type ");
}
}
}
}
& No error message will be reported if the specified type is not determined.

2. The as operator is similar to forced type conversion. If the conversion fails, no error is reported. Only a null value is returned.

Using system;
Using system. Collections. Generic;
Using system. LINQ;
Using system. text;

Namespace istext
{
Class Program
{
Static void main (string [] ARGs)
{

String STR = "Hello World ";

Object S = STR as object;
If (s! = NULL)
{
Console. writeline ("conversion successful !!! ");
Console. writeline (S. tostring ());
}
Else
{
Console. writeline ("Conversion failed ");
}
}
}
}