How To Convert StringBuffer To String

I want to convert the StringBuffer in to String . I have used this code but gives compile error.

import java.io.*;
import java.util.*;
import javax.mail.*;
import java.sql.*;
public class REPLACE {
static StringBuffer s= new StringBuffer("ABCD");
public static void main(String args[]) throws Exception

[Code] ....

C:jdk1.6.0_04bin>javac REPLACE.java
REPLACE.java:15: cannot find symbol
symbol : method to_String()
location: class java.lang.StringBuffer
rep = s.to_String();
^
1 error