Error Compiling Java in Oracle 10g

I can compile the following Java code just fine when using the Java compiler. But I am getting an error when trying to compile the source file in Oracle.

Here is the code:

create or replace and compile java source named host as import java.io.* ;
import java.sql.* ;

public class Host
{

public static final void RewriteBaim10Pmc( ) throws IOException
{

try
{

BufferedReader inputStream = new BufferedReader(new FileReader("/ interface/nwps/BAIM/data/if_baim10pmc_pre.dat")) ; PrintWriter outputStream = new PrintWriter(new FileWriter("/interface/ nwps/BAIM/data/if_baim10pmc.dat")) ;
StringBuilder buffer = new StringBuilder() ;

// more code
inputStream.Close() ;
outputStream.Close() ;
}}}

Here is the error message that Oracle is giving me:

Errors for JAVA SOURCE HOST:

LINE/COL ERROR

0/0 HOST:7: cannot resolve symbol
0/0 symbol : class StringBuilder
0/0 location: class Host
0/0 StringBuilder buffer = new StringBuilder() ;
0/0 ^
0/0 2 errors
0/0 symbol : class StringBuilder
0/0 location: class Host
0/0 StringBuilder buffer = new StringBuilder() ;
0/0 ^
0/0 HOST:7: cannot resolve symbol