问题
Possible Duplicate:
StringBuilder and StringBuffer in Java
Criteria to choose among StringBuffer and StringBuilder
回答1:
If you're definitely using Java 5 or higher, and you definitely don't need to share the object between threads (I can't remember ever needing to do so), StringBuilder is a better bet.
Basically you should almost always use StringBuilder when you can, to avoid pointless synchronization. Admittedly the way most VMs handle uncontended synchronization is extremely efficient, but if you don't need it in the first place...
回答2:
StringBuilder methods are not synchronized, so when you are not concerned with multithreading part you can use it, as it would be fast.
StringBuffer on the other hand have all its method synchronized, and hence is thread safe.
You can go through this post: - Difference between StringBuilder and StringBuffer
来源：https://stackoverflow.com/questions/12961254/stringbuffer-stringbuilder-when-to-use