String builder new code example

Example 1: stringbuilder 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.

Example 2: why string builder

StringBuilder is for, well, building strings.
Specifically, building them in a very
performance way. The String class is good
for a lot of things, but it actually has
really terrible performance when assembling 
a new string out of smaller string parts
because each new string is a totally new,
reallocated string.