What you need is to pass it to File2.java, so assuming that you have something like so:
public class File2
{
...
//Constructor
public File2(...)
...
}
You would need to change it like so:
public class File2
{
....
String userName = "";
public File2(...String userName...)
{
this.userName = userName;
...
}
....
}
And call it like so (from your File1 class):
String user = jTextField1.getText();
...
File2 file2 = new File2(..., user, ...);
Alternatively, instead of passing the userName field, you can pass an instance of File1 to your File2 class and expose whatever fields you want to access through Field2 by creating the appropriate get methods in your File1 class. This usually comes in handy when you need to access more than one field.