Flow Control - SCJP Sun Certified Programmer for Java Platform SE6 - page 246

7. “address must be set first”);
8. }
9. System.out.println(“Shipping order...”);
10. }
11. }
Invoking shipOrder on a CustomerOrder object with a null address fi eld results in the
following exception:
Exception in thread “main” java.lang.IllegalStateException: address must be set
first
at CustomerOrder.shipOrder(CustomerOrder.java:6)
at CustomerOrder.main(CustomerOrder.java:12)
NullPointerException
A NullPointerException is thrown when a null reference is used in situations where an
actual object is required. This exception is one that is thrown frequently by both the JVM
and programmatically. For example, the JVM throws a NullPointerException in the
following code:
3. Integer x = null;
4. System.out.println(x.intValue());
The reference x is null, so attempting to invoke any method on it results in a
NullPointerException . The stack trace looks like:
Exception in thread “main” java.lang.NullPointerException
at NullPointerDemo.main(NullPointerDemo.java:4)
Programmatically, you can throw a NullPointerException if you know a reference is
null . For example, the following method throws a NullPointerException if the argument
passed in is a null reference:
public void printMessage(String message) {
if(message == null) {
throw new NullPointerException(“message cannot be null”);
}
System.out.println(message);
}
NumberFormatException
A NumberFormatException is thrown when a string is parsed into a numeric value and the
string does not have the appropriate format. The exception is thrown by the parsing and