Java Reference
In-Depth Information
So when do you use
StringBuffer
objects rather than
String
objects?
StringBuffer
objects
come into their own when you are transforming strings - adding, deleting, or replacing substrings in a
string. Operations will be faster and easier using
StringBuffer
objects. If you have static strings,
which you occasionally need to concatenate, then
String
objects will be the best choice. Of course, if
you want to you can mix the use of both in the same program.
Creating StringBuffer Objects
You can create a
StringBuffer
object that contains a given string with the statement:
StringBuffer aString = new StringBuffer("A stitch in time");
This declares a
StringBuffer
object,
aString
, and initializes it with the string
A
stitch
in
time
.
When you are initializing a
StringBuffer
object, you must use this syntax, with the keyword
new
,
the
StringBuffer
class name, and the initializing value between parentheses. You cannot just use the
string as the initializing value as we did with
String
objects. This is because there is rather more to a
StringBuffer
object than just the string that it contains initially, and, of course, a string literal is a
String
object by definition.
You can just create the
StringBuffer
variable, in much the same way as you created a
String
variable:
StringBuffer myString = null;
This variable does not refer to anything until you initialize it with a defined
StringBuffer
object. For
example, you could write:
myString = new StringBuffer("Many a mickle makes a muckle");
which will initialize it with the string specified. You can also initialize a
StringBuffer
variable with
an existing
StringBuffer
object:
myString = aString;
Both
myString
and
aString
will now refer to a single
StringBuffer
object.
The Capacity of a StringBuffer Object
The
String
objects that we have been using each contain a fixed string, and memory is allocated to
accommodate however many Unicode characters are in the string. Everything is fixed so memory usage
is not a problem. A
StringBuffer
object is a little different. It contains a block of memory called a
buffer
, which may or may not contain a
String
, and if it does, the string need not occupy all of the
buffer. Thus the length of a string in a string object can be different from the length of the buffer. The
length of the buffer is referred to as the
capacity
of the
StringBuffer
object.
Once you have created a
StringBuffer
object, you can find the length of the string it contains, by
using the
length()
method for the object:
