615: Mainline

The Java compiler attempts to be smart, anticipating potential exceptions and forcing you to acknowledge those potential exceptions.

Sometimes, however, Java does not detect a potential exception at compile time, but encounters an exception at run time nevertheless. Java compiles the following demonstration program without complaint, but throws an ArrayIndexOutOfBoundsException, because the array has no element indexed by 3:

public class Demonstrate { 
 public static void main(String argv[]) { 
  int [] threeElements = {1, 2, 3}; 
  for (int counter = 0; counter < 4; ++counter) { 
   System.out.println(threeElements[counter]); 
  } 
 } 
}