why this program always different time for (for loop)

Question

long start, end;
System.out.println("Timing a for loop from 0 to 100,000,000");
// time a for loop from 0 to 100,000,000
start = System.currentTimeMillis();
for(long i=0; i < 100000000L; i++) ;
end = System.currentTimeMillis();
System.out.println("Elapsed time: " + (end-start));

Answer 1

Because the speed of the compiler isn't always the same