13. Difference between String, StringBuilder, and StringBuffer code example

Example 1: string vs stringbuffer

The main similarity between String and StringBuffer class is that both are
thread safe. 
The main difference is that String is immutable; StringBuffer is mutable.

Example 2: stringbuilder vs stringbuffer

They both mutable, they are exactly same but
String buffer is thread safe so it runs slower
than String builder.
We are using StringBuffer when we are doing parallel
testing since it is a thread safe.