Difference between StringBuilder and StringBuffer

Question

What is the main difference between StringBuffer and StringBuilder? Is there any performance issues when deciding on any one of these?

Answer 1

The javadoc explains the difference:

This class provides an API compatible with StringBuffer, but with no guarantee of synchronization. This class is designed for use as a drop-in replacement for StringBuffer in places where the string buffer was being used by a single thread (as is generally the case). Where possible, it is recommended that this class be used in preference to StringBuffer as it will be faster under most implementations.