How can Polymorphism replace an if-else statement inside of a loop?

How can polymorphism replace an if-else statement or Switch inside of a loop? In particular can it always replace an if-else? Most of the if-thens I use inside of loops are arithmetic comparisons. This question is spawned from this question.

int x;
int y;
int z;

while (x > y)
{
     if (x < z)
     {
         x = z;
     }
}

How would this work with polymorphism?
NOTE: I wrote this in Java but am interested in this for any OOL.