Re: Vector efficiency

From:

"Oliver Wong" <owong@castortech.com>

Newsgroups:

comp.lang.java.help

Date:

Wed, 30 Aug 2006 13:48:52 GMT

Message-ID:

<8HgJg.19542$365.3633@edtnps89>

"Tux2" <matteo.franci@gmail.com> wrote in message
news:1156928799.172132.108410@m73g2000cwd.googlegroups.com...

Even if the best collections depends on the type of operations you need
to perform, as a rule of thumb you can use :
array - for operating on fixed number of elements (you know how many
element tou will use and the number will not change in time).
java.util.List - are the best choice in case of modifiable collections
(adding, removing etc).

We need to say that java.util.Vector is only a possibile implementation
of java.util.List.

If you need synchronization (i.e. you collection is shared among
multiple threads) than you need to use java.util.Vector (and take any
other concern involved in synchronization).

If you don't need synchronization than java.util.ArrayList ot
java.util.LinkedList may be a better choice. In particular the first is
better when tou mostly access and add elements to the end of the list,
while the second is better while removing and adding elements at random
point.

    A clarification:

ArrayList:
    Pro: Can read from random points in the array in O(1) (i.e. quickly).
    Con: Slow to add or remove elements (needs to copy the array, which is
O(n), i.e. slow)

LinkedList:
    Pro: Can add or remove elements relatively quickly into the head or tail
of the list (O(1)); adding elsewhere in this involves a seek which is
somewhat slow O(n)
    Pro: Can read from the head or tail quickly O(1), but seeking to a
random element in the middle of the list is slow (O(n)).

If you know your collection won't have duplicates and order isn't important,
or you want to use the object's natural ordering, you may consider HashSet
and TreeSet as well, which are optimized for a different set of operations.

    - Oliver