1) You mean to copy files, right?? Try using class  java.io.File or
java.io.RandomAccessFile. I'm sorry, I can't give you the code yet,
but if you have the java  Documentation, you can search it for more
reference. But if I have time, maybe I can try and give you the code.

2)As far as I can remember, "trim()" only delete  spaces in front and
back of string, so if your original string  is " This is a
string ", and you call  trim(), the result will be "This is a
string". Here is the code :
String myString = new String(" This is a string ");
String myString2 = myString.trim();
myString2 will be "This is a string"

3) I don't know

4) Have you set your classpath correctly??? Or maybe you can consider
using NetBeans IDE (http://java.sun.com/j2se)