330 Java Tips.pdf - FTP Server

General Java Questions I
Q: Is it possible to use switch with range of values?
Ex:
switch (iBegins){
case 2 to 10:
}
Answer:
not exactly like this but:
switch (iBegins){
case 2:
case 3:
case 4:
case 5:
case 6:
case 7:
case 8:
case 9:
case 10:
/* do stuff */
break;
case 11:
/* other stuff */
}
Jan Schaumann
Q: Is there a general reason why nullpointer exceptions occur?
Answer: Of course there is. A NullPointerException happens when you have a
reference, it's set to null (or is a class or instance variable and has never been
initialized), and you try to perform some operation on the object it points to. Since it
really doesn't point to an object, you can't do that.
--
Chris Smith
Q: I am aware that the exceptions in the catch statements must be of the same
type or a super type of the exception thrown in the try block.
My question is this:
Is there any significance in the ordering of the catch statements after a try block?
Answer: It is required to design you catch statement sequences with most derived
exception class type first and progressing to the highest superclass. Else, the code
will not compile.
For a obvious reason, if the a catch block for a given class precedes a catch block for
a type that is derived from the first, the second catch block will never be executed.
--
D. Michael Nelson
Q: I wrote a program that use a few RS232 ports. The operators are unskilled
and often start multiple instances of the program. Will someone please be so kind
and tell me how I can prevent them doing it?
Answer 1: The first instance might write a file. Subsequent instances could check for
the existence of that file, or else check it's contents.
Another method could involve creating a server socket on a specific port. Subsequent
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