StringBuffer no longer shares its contents with the Strings it creates in 1.5. Apparently enough people found the shared buffer behavior unexpected and confusing that Sun didn't even bother adding a toStringWithoutCopy() method for those who want that behavior.
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Posted by weitzman on August 3, 2005 2:29:05 PM EDT
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Re: StringBuffer.toString() doesn't share contents in 1.5
I was done because String never really was thread-safe. In 5.0, with the new Java Memory Model, it is.
Comment from Tom Hawtin on August 4, 2005 8:08:58 PM EDT
It wasn't confusion that made them kill the feature, it was the potential for massive memory leaks that did it in. Check the Sun bug database it's in there. But a quick example would be stuffing a StringBuffer with text from a file and running a regex over it. Your regex finally matches so you say return regex.group(). Now, the substring you matched contains 10 chars of a 1,000,000 char array, which can't get GC'ed because you are holding on to 10 of them.
Comment from studdugie on August 10, 2005 8:54:57 PM EDT
There are two more reasons:
1. It is a security risk, because characters in the String could be viewed/changed from the StringBuffer.
2. It can be more efficient to reuse a StringBuffer or StringBuilder (via the delete method) when making similar strings (e.g. the same prefix), sharing makes this practice unsafe. I use my own StringBuilder class in Java 1.3 and 1.4, with copy on toString(), to resolve this problem and avoid the synchronized performance hit for local code.
Comment from Infernoz on August 13, 2005 2:09:31 PM EDT
Correction, the characters in the String can't be indirectly since the String constructor flags the StringBuffer as shared, however this makes the StringBuffer more complex and slower, because it has to check the shared flag in all modication methods, and as stated earlier can cause serious memory leaks.
Comment from Infernoz on August 13, 2005 2:20:41 PM EDT
Third try; "edit" link wanted!
There are two more reasons:
1. The StringBuilder shared flag slows it down because it has to be checked for and a new, possibly badly sized, char array allocated.
2. It can be more efficient to reuse a StringBuffer or StringBuilder when making similar strings (e.g. the same prefix), sharing makes this practice unsafe. I use my own StringBuilder13 class in Java 1.3 and 1.4, with new String(value, 0, count) for toString(), to resolve this problem and avoid the synchronized performance hit for local code.
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