I do see a couple of problems here.
- The first one is the one you're concerned with. The common backslash is usally an escape character in strings to denote special characters like a tabulator via \t. So if you want to include a backslash in your strings you have to escape it with a backslash: \\.
- The second point is that a file path is not a URL. If you want to know the proper syntax for file URLs you should google exactly that: "File system URLs".
- I'm not sure what exactly you're trying to achieve, but groping around in the file system in the java installation's bin folder looks really fishy to me. I'm not sure an applet container would even allow the access to that folder on the clients computer.