Java StringBuilder huge overhead

Question

I read somewhere that the Java StringBuilder uses around 1 mb for 500 characters. Is this true and if so, isn't that a bit extreme? Is the StringBuilder doing some incredible things with this amount of memory? What is the reason and does this mean I should not make too much use of this class?

Somewhere on the Internet, of course. – Bart Kiers Nov 10 '09 at 14:34 — Bart Kiers, Nov 10 '09 at 14:34

score 14 · Answer 1 · answered Nov 10 '09 at 11:41

No, that's complete rubbish - unless you create a StringBuilder with a mammoth capacity, of course.

Java in general uses 2 bytes per char. There's a little bit of overhead in String and StringBuilder for the length and the array itself, but not a lot.

Now 1K for 500 characters is about right... I suspect that was the cause of confusion. (Either you misheard, or the person talking to you was repeating something they'd misheard.)

score 2 · Answer 2 · answered Nov 10 '09 at 12:26

I have seen two cases where StringBuilder's tend to use large amounts of memory:

When the StringBuilder is created with an insane initial-capacity.
StringBuilder's who were "cached" to "save" object-allocation time.

So in the second case a StringBuilder might consume 1Mb of memory if some code, which used the SB earlier, stored a very big string in it. That's because it will only grow but not shrink its internal char-array.

Both cases can (and should) easy be avoided.

score 0 · Answer 3 · answered Nov 10 '09 at 11:46

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This information is erroneous, do you remember what the source of this information was? If so you should correct it. Java normally uses 2 bytes per character.

answered Nov 10 '09 at 11:46

Tendayi Mawushe

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score 0 · Answer 4 · edited May 23 '17 at 11:47

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Because of the doubling reallocation 2K for 500 characters would also be right, but not more. Here is a similar question.

edited May 23 '17 at 11:47

Community

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answered Nov 10 '09 at 11:48

candiru

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score 0 · Answer 5 · answered May 05 '17 at 17:42

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I think StringBuilder is the best choice to use. It is faster and safer too. It depends on the scenario. If you have String literal that doesn't change frequently then I would say String is a better choice because it is immutable else StringBuilder is right there. Now for the space that you are talking about I haven't heard that any where.

answered May 05 '17 at 17:42

Mike

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Faster than what? Safer? Be aware that StringBuilder is _not_ thread safe, in contrast to StringBuffer. BTW this question is almost 8 years old... – Andy May 05 '17 at 17:56
Faster than StringBuffer.Anythng else you need to understand. – Mike May 05 '17 at 18:11

Java StringBuilder huge overhead

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