Beginning with JDK 1.4, a new feature has been incorporated into the exception subsystem: chained exceptions. The chained exception feature allows you to associate another exception with an exception. This second exception describes the cause of the first exception. For example, imagine a situation in which a method throws an ArithmeticException because of an attempt to divide by zero. However, the actual cause of the problem was that an I/O error occurred, which caused the divisor to be set improperly. Although the method must certainly throw an ArithmeticException, since that is the error that occurred, you might also want to let the calling code know that the underlying cause was an I/O error. Chained exceptions let you handle this, and any other situation in which layers of exceptions exist.
To allow chained exceptions, two constructors and two methods were added to Throwable.
Throwable(Throwable causeExc)
Throwable(String msg, Throwable causeExc)
Example of chained exception
class ChainExcDemo {
static void demoproc() {
// create an exception
NullPointerException e =
new NullPointerException("top layer");
// add a cause
e.initCause(new ArithmeticException("cause"));
throw e;
}
public static void main(String args[]) {
try {
demoproc();
} catch(NullPointerException e) {
// display top level exception
System.out.println("Caught: " + e);
// display cause exception
System.out.println("Original cause: " +
e.getCause());
}
}
}
The output from the program
Caught: java.lang.NullPointerException: top layer
Original cause: java.lang.ArithmeticException: cause