Array size, how to trim?

Programming Questions

leerraum

in Programming Questions • 3 years ago

Hi,
I want to use an array instead of an ArrayList, but I'm not sure if I got the manual right. Is it right that I must define the arrays number of elements in advance?

In the case of my script I know the maximum number of possible elements that could emerge. But I'm not sure if they will. So is it possible to set an arrays size to the maximum number of possible elements and if the array is not filled completly to trim it down to it's real size?

( Or: How can I resize an array on runtime? )

Thanks!
leerraum

Replies(5)

kevin.bjo..

Re: Array size, how to trim?

3 years ago

Dynamic sizing is why Java has ArrayList and other Container classes -- basic arrays are fixed-size once declared (as they are in, say, C, but not as they are in, oh, mel).

Is there a compelling reason for using an array instead of a class type, or is it just a matter of being comfortable with coding arrays? (less typing)?

kb, http://www.riftgame.com/

PhiLho

Re: Array size, how to trim?

3 years ago

Well, if you know the maximum size and if it isn't not enormous (megabytes), just keep the array as it is.
Processing offers operations to shorten() arrays, but all it does is to create a new, smaller array and copy the data to keep there.

leerraum

Re: Array size, how to trim?

3 years ago

ok, thanks! I'm stumpled accross javas vector class yesterday. This does excactly what I need. Just one question: is Vector faster than ArrayList?

PhiLho

Re: Re: Array size, how to trim?

3 years ago

No, it is slower. It is synchronized (related to threads), so each operation is wrapper and thus slower.
Beside, it is older than ArrayList. Old Java coders tend to use the former instead of the latter, out of habits.
Prefer ArrayList to Vector and HashMap to Hashtable.

niteshade

Re: Array size, how to trim?

3 years ago

you can time operations with millis()

http://processing.org/reference/millis_.html

e.g.

startTime = millis();
//operations
endTime = millis();
duration = endTime - startTime;
println(duration);