Just pass it as a String object to setRemoteHost(). I tried the following (Windows envirnment) and it worked:
MSDOS Batch file:
set JAVA_HOME=<your path to java>
set CP=.;..\lib\edtftpj.jar
%JAVA_HOME%\bin\java -classpath %CP% Demo %1 %2 %3
Commandline (MSDOS shell):
demo 1.2.3.4 username pass1234
The arguments are, of course, passed as String objects to the 'main' method. The same thing shoud apply in a GUI. Or, to create a String object directly:
String host = new String("1.2.3.4");