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?

• McDowell: Where did you read this?
• Bart Kiers: Somewhere on the Internet, of course.

Answer 1

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.)

Answer 2

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.

Answer 3

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.

Answer 4

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

Answer 5

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.

• Andy: Faster than what? Safer? Be aware that StringBuilder is not thread safe, in contrast to StringBuffer. BTW this question is almost 8 years old...
• Mike: Faster than StringBuffer.Anythng else you need to understand.