Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!feeder.erje.net!eu.feeder.erje.net!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail
From: Robert Klemme <shortcutter@googlemail.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: BitSet vs boolean[]
Date: Fri, 18 Jul 2014 21:11:42 +0200
Lines: 24
Message-ID: <c2t9rfFg9d0U1@mid.individual.net>
References: <63ris9524feapq3fe288pv7lj1mdpoj444@4ax.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
X-Trace: individual.net UBGBL6salfzYZLJnbntiBgsWN+x9/KpoEWz9mwlfS9kKZpCAQ=
Cancel-Lock: sha1:hBH/eTYon0UcvT0xZEwZ1Uw6RNs=
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0
In-Reply-To: <63ris9524feapq3fe288pv7lj1mdpoj444@4ax.com>
Xref: csiph.com comp.lang.java.programmer:29119

On 18.07.2014 20:51, Roedy Green wrote:
> In terms of minimising space, how big must a boolean array be before
> it pays to use a BitSet?

Well, a BitSet has these members
- long[]
- int
- boolean

If I'm not mistaken that yields sizeof(ref) + 8 * length + 4 + 4 = 
sizeof(ref) + 8 * (length + 1) bytes with length > 0 so at least 
sizeof(ref) + 16 bytes.  I'd say worst case this is 8 + 16 = 24 bytes. 
Sinze a BitSet grows dramatically slower (on average 8 times) than a 
byte array if you add items that should be the max size.

Of course, you can save even more memory by using a byte, short, int or 
long if you know the max set size is 8, 16, 32 or 64 bits and implement 
all the operations via bit logic.

Kind regards

	robert