Hi Author!

i am reading chap 13 in Java2 sdk1.4.

in page 512, it was written that "The index value must be less than or equal to the size of the Vector..." . again in the next paragraph it was written "If you specify an index value argument that is negative, or greater than or equal to the size of the Vector, the method will through an ArrayIndexOutOfBoundsException".

is it confusing or am i getting confused???

Thanq,
Hanuman

An index value for a vector cannot be negative, nor can it be greater than the size of the vector, otherwise it will throw an exception.

Cheers

Martyn

The containers in programming, like array, vector or other datastructures are zerobased. That means that the first element is number '0'. So if a vector has two elements ( or objects ), the first one has the index( number ) '0', and the second has the index '1'. The third element has the number 3 - 1 = 2, so in a Vector that have 100 elements the last element has the number 99 ( again, because you begin to count from zero ). So if a Vector has 100 elements, and you try to axcess element number 100, you are trying to axcess .....nothing, then: ArrayIndexOutOfBoundsException
hope you understand this
Rune

I think the confusion is due to the fact that the book mistakenly says that a valid index must be <= the array size. This, as you both have mentioned, is incorrect since the largest valid index value is the array size - 1.


I think it's a typo in the book -- check if an errata page for the book exists. If so, check to see if this is already listed there. If not, submit it as a new error.


Also, Rune: There are several programming languages that begin numerically indexed arrays as 1, not 0, so you don't want to generalize that "containers in programming... are zero based." Numerically indexed arrays and vectors in Java, C, and C++ certainly are zero based, but by no means are ALL containers in ALL languages zero based.

In fact, it's REALLY REALLY easy to write a simple wrapper class around a java (or C++, etc..) vector that creates a 1-based vector.


Take care,

Nik
http://www.bigaction.org/

Sorry Nik
I did generalize to much. I don' know all programming language, but some, as you say C, C++ and Java and took a shortcut and made a too fast generalization. But that write a wrapper class that is not zero-based is not a good argument.
Generalization is infact a common trap. Too many people go into it. Thanks for telling me, so I could see it, and be more carefull next time!
Rune