The principal operations on a StringBuilder are the
append and 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 "startle", whereas
z.insert(4, "le") would alter the string builder to
In general, if sb refers to an instance of a StringBuilder,
then sb.append(x) has the same effect as
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.
Instances of StringBuilder are not safe for
use by multiple threads. If such synchronization is required then it is
recommended that StringBuffer be used.
quicker than String a + String b