StringBuffer in Java is used as a thread-safe, mutable sequence of characters, replaced by StringBuilder in Java 5.0+
A thread-safe, mutable sequence of characters. A string buffer is like a String, but can be modified. At any point in time it contains some particular sequence of characters, but the length and content of the sequence can be changed through certain method calls.
In Java 5.0, it was replaced by StringBuilder as this was faster, and there was almost not good use case for a thread safe StringBuffer and classes which attempted to use it as such ended up not being thread safe anyway. e.g. SimpleDateFormat.
The Javadoc for StringBuffer notes
As of release JDK 5, this class has been supplemented with an equivalent class designed for use by a single thread, StringBuilder. The StringBuilder class should generally be used in preference to this one, as it supports all of the same operations but it is faster, as it performs no synchronization.
