WHat does the stringbuilder do code example

Example: what is stringbuilder used for in java

Java StringBuilder class is used to create
  mutable (modifiable) string. The Java
  StringBuilder class is same as StringBuffer
  class except that it is non-synchronized.
    
StringBuilder()
    creates an empty string Builder with the initial capacity of 16.
StringBuilder(String str)
    creates a string Builder with the specified string.
StringBuilder(int length)
    creates an empty string Builder with the specified capacity as length.