As Adam Sackfield stated : he is using "a" and "b" as they are shorter than foo and bar. The entire code probably looks like this:

class example  {
      public static void main(String[] args){

//declare your function int funky_math(int a, int b); int main() { int foo = 24; int bar = 35; printf("funky math\n" +
 funky_math(foo, bar)); return 0; }

int funky_math(int a, int b);

int main(){

           int foo =24;
           int bar =35;

           system.out.println("funky math" + funky_math(foo,bar)); //this part is where the values of foo and bar are passed to a and b.
           return 0;
}
    }
}

what's going on here is a little bit of Algebra.

So what he's doing is called "passing" the values, it is annoying and confusing sometimes to keep track of the variables but its kind of like the transitive property of equality theorem: A=B & B=C SO A=C; or perhaps reflexive property of equality: A=A , B=B;

so in this case: a = foo b = bar

So rather than typing out foo and bar every time you right an equation we can substitute the variable names as A and B. But this also allows the int funky_math() method to remain unchanged manually whereas the variables of the main() method will mostly likely change throughout the program. It's just more efficient code to write it this way. I hope this helps, once you see this a couple of times it starts to click more just practice practice practice! let me know if i need to elaborate more (: