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When should I use StringBuffer instead of String?

Charles McGuire
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Joined: Jan 18, 2005
Posts: 99
I'm a little confused about when to use StringBuffer instead of String. StringBuffer, I'm told, will perform better than String.

Wouldn't it be better to always use StringBuffer? When would I use one over another?

Right now I'm working with JavaBeans and factories. It would seem that Sring would be better used in the JavaBean, and maybe StringBuffer should be used in the Factory.

Any guidance from the experienced ranch hands?


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Ernest Friedman-Hill
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Joined: Jul 08, 2003
Posts: 24183

A String is a string. A StringBuffer is a tool for building Strings.

When you need to pass an argument to a method named, say, setName(), the argument, presumably a "name", ought to be a String. When you need to return something from a method named, say, getName(), and it's supposed to return the "name" of something, then that method should return a String.

But let's say you have an array containing the names of the 50 states, and you need to loop over that array and build a comma-separated sentence like

"The 50 states are Alabama, Alaska, Arkansas..."

then you'll want to use a StringBuffer to accumulate the result, rather than using Strings and the "+" operator; it will be much more efficient.

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Max Habibi
town drunk
( and author)

Joined: Jun 27, 2002
Posts: 4118

Be aware that StringBuffers have synchronized methods, which can be expensive. Accordingly, if you're not writing multithreaded code, consider using the StringBuilder class in Java 5.0.


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Layne Lund
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Joined: Dec 06, 2001
Posts: 3061
Ernest's example illustrates a certain situation where you should prefer StringBuffer over String. To generalize this a little, StringBuffer should be preferred when you are building a string. Whereas String is useful when the string is "static" (i.e. its contents don't change except to replace it by a completely new and unreleated string).



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Lionel Badiou
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Joined: Jan 06, 2005
Posts: 140
Hi Charles,

Another noticeable point is :

* String CAN'T be modified (a process on a String will always return a new string as a result)
* StringBuffer CAN be modified (a process on StringBuffer really modifies the content of a StringBuffer)

You may look at the reasons here: http://java.sun.com/docs/books/tutorial/java/data/whytwo.html

Best regards,

Lionel Badiou
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Lionel Badiou
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Joined: Jan 06, 2005
Posts: 140
oops ;-)

The reason is here : Why two string classes ?

Dave Lenton
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Joined: Jan 20, 2005
Posts: 1241
There's a good comparison of Strings and StringBuffers here:


The conclusion is worth noting:

# Within a single string assignment, using String concatenation is fine.
# If you're looping to build up a large block of character data, go for StringBuffer.
# Using += on a String is always going to be less efficient than using a StringBuffer, so it should ring warning bells - but in certain cases the optimisation gained will be negligible compared with the readability issues, so use your common sense.

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