Dealing with Java - Multimedia Introduction to Programming Using Java - page 482

at the time, and this can be helpful. But it contains a bit more. To illustrate, we
change the program so that the division by 0 occurs within a different method:
public class Ex {
public static void main(String[] args)
{ first(); }
public static void first()
{ second(); }
public static void second()
{ System.out.println( 5 / 0 ); }
}
Suppose method main is called. Method main calls first , which calls sec-
ond , which divides by 0 . The list of calls that have been started but have not com-
pleted is called the call stack . When the division by zero occurs, the same excep-
tion is thrown, and the following appears in the Java console:
java.lang.ArithmeticException: / by zero
at Ex.second(Ex.java:7)
at Ex.first(Ex.java:5)
at Ex.main(Ex.java:3)
As before, the first line says that an ArithmeticException occurred, which
was a division by zero. The second line says that the exception occurred in sec-
ond , at line 7 of file Ex.java . The third line says that second was called from
first , and the fourth line says that first was called from main .
Thus, when an exception occurs:
A message on the Java console describes the call stack: the stack
of methods that have been called but have not yet completed.
You can use this stack of calls to help figure out how your program got to the
point of throwing the exception.
If your program aborts with one of these errors, there is a severe problem:
OutOfMemoryError
InternalError
UnknownError
In the first case, you have to find out why your program used too much memo-
ry. In the other two cases, it is difficult to say what to do. Something caused
things to become really messed up. Perhaps recompiling all files may help.