C # is cast

1.is: Check that the object type is compatible with the enactment type. Back to True,false

BOOL x = A is b;

2.as: Efficiency is higher than is

Because B is a parent class, a subclass can be converted to a parent class, so B is not equal to NULL, no output

 Public classMain { Public Static voidMain () {A A=NewA (); b b= A asB; if(b = =NULL) {Console.WriteLine ("---"); }        }    }    classa:b{}classb{}

In contrast to the above scenario, the output---

 Public classMain { Public Static voidMain () {A A=NewA (); b b= A asB; if(b = =NULL) {Console.WriteLine ("---"); }        }    }    classa{}classb:a{}

C # is cast