Re: Vector<T> length in bytes
ivan.kataitsev@gmail.com wrote:
If you want to fit your objects into a byte [], you need to design a
custom method to do that. Java can't even convert a Vector to a byte
[], so there's no way to get the size of said byte[] either.
But the number of the elements of the byte[] is the size of byte[] in
bytes, isnt it?
No. byte [] will occupy a bit more than that because, at minimum, the
reference will use up a few bytes too. In other words, byte [] b = new
byte[10]; will occupy about 18 bytes, at least, because a reference (the
"b") takes up about 8 bytes on it's own.
And I don't think you are guaranteed that the JVM is using octets (fancy
word for bytes) to implement the byte type in Java. It could be using
machine words which might be 4 bytes long. So the array about might be
48 bytes - 8 bytes for the reference and 4 bytes each for the elements,
each of which will have 3 bytes unused.
Java is not C. Java is a long ways away from the machine. It does that
for portability. If you need access to machine elements like real
bytes, you should use C. So that brings me back to, why do you need this?
I found some stuff that I was looking for before I sent my first post:
You can use java.lang.Runtime to determine how much memory you have
left, and how much you are using. If you make lots of Vector<T>'s you
can get a statistical approximation to the amount of space they occupy.
That's what I've seen done for other sorts of objects. Do a search
for "java memory footprint" I think you'll find the articles describing
what I'm talking about. That's how I know a reference is about 8 bytes
most of the time, because other folks have done the research.
<http://java.sun.com/javase/6/docs/api/java/lang/Runtime.html>
<http://java.sun.com/docs/books/performance/1st_edition/html/JPRAMFootprint.fm.html>