Strings and Regular Expressions - The Java Programming Language - page 492

The insert methods take two parameters. The first is the index at which
to insert characters into the StringBuilder . The second is the value to
insert, after conversion to a String if necessary. Here is a method to put
the current date at the beginning of a buffer:
public static StringBuilder addDate(StringBuilder buf) {
String now = new java.util.Date().toString();
buf.insert(0, now).insert(now.length(), ": ");
return buf;
}
The addDate method first creates a string with the current time using
java.util.Date , whose default constructor creates an object that repres-
ents the time it was created. Then addDate inserts the string that repres-
ents the current date, followed by a simple separator string. Finally, it
returns the buffer it was passed so that invoking code can use the same
kind of method concatenation that proved useful in StringBuilder 's own
methods.
The reverse method reverses the order of characters in the StringBuild-
er . For example, if the contents of the buffer are "good" , the contents
after reverse are "doog" .
You can remove part of the buffer with delete , which takes a starting
and ending index. The segment of the string up to but not including the
ending index is removed from the buffer, and the buffer is shortened.
You can remove a single character by using deleteCharAt .
You can also replace characters in the buffer:
public StringBuilder replace(int start, int end, String str)
Replace the characters starting at start up to but not includ-
ing end with the contents of str . The buffer is grown or shrunk
as the length of str is greater than or less than the range of
characters replaced.