why is this not possible .can any one explain?
String builder is a final class. so not possible.
A mutable sequence of characters. 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.
The principal operations on a
StringBuilder are the
insert methods, which are overloaded so as to accept data of any type. Each effectively converts a given datum to a string and then appends or inserts the characters of that string to the string builder. The
append method always adds these characters at the end of the builder; the
insert method adds the characters at a specified point.
For example, if
z refers to a string builder object whose current contents are "
start", then the method call
z.append("le") would cause the string builder to contain "
z.insert(4, "le") would alter the string builder to contain "
In general, if sb refers to an instance of a
sb.append(x) has the same effect as
sb.insert(sb.length(), x). Every string builder has a capacity. As long as the length of the character sequence contained in the string builder does not exceed the capacity, it is not necessary to allocate a new internal buffer. If the internal buffer overflows, it is automatically made larger.
StringBuilder are not safe for use by multiple threads. If such synchronization is required then it is recommended that
StringBuffer be used.