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For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))
How big shall I make my array?

Posted by enquirer (enquirer), 8 October 2002
I don't know how big to make an array when I'm writing my program. Should I just make it big enough to deal with any eventuallity?

Posted by admin (Graham Ellis), 8 October 2002
Java uses a dynamic memory model rather than a static one, so you don't need to decide on the size of your arrays at the time you compile your code.

If you can work out how big an array needs to be at run time, but before you write anything to it, you can simply set it up using a variable or expression to tell your Java Runtime Environment how big to make the array for this particular run.

Once an array is dimensoned, it cannot dynaically extend (as it can in languages like PHP), but you could create a new array that's longer than the original, copy all the elements, then copy the new reference over the old one.
NOT recommended - inefficient!

The best solution is to use a Vector or an ArrayList (see the java.util package), which lets you handle more dynamic "collections".   These are held rather differently within your memory, so can be expanded and contracted on the fly.  If you need to be very efficient, there are methods available to copy these collection objects into arrays once they're fully populated and you know they won't grow any further.

Posted by admin (Graham Ellis), 1 December 2002
Just a footnote ...

"Changing the size of an array in Java" is a very common question - lots of people come to our training web site having entered a Google query along those lines.    Really the text above provides the background of an answer - in summary

* If you know how big it will be BEFORE you write any data into an array, you can change the size from one instant to the next.

* If you don't know how big an instance of an array will be before you write the first data into it, use an ArrayList or a Vector even if you do copy it into an array for more efficiency later in your program.



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