Java file path best practices

If the operating system is windows, which of the following is the best way to write in Java?

1)

String f = "some\\path\\file.ext";

2)

String f = "some/path/file.ext";

3)

String f = "some"+File.separator+"path"+File.separator+"file.ext";

4)

String f = new StringBuilder("some").append(File.separator).append("path").append(File.separator).append("file.ext").toString();

Solution

Editor: in view of the comments, I should clarify It absolutely depends on the background What would you do? If you try to create a file path in the "native" operating system format, I will use option 5, file:

File f = new File("some");
f = new File(f,"path");
f = new File(f,"file.ext");

Or better, put this logic into the method:

public static File newFile(String root,String... parts) {
    // TODO: Check that nothing's null (root,parts,each element of parts)
    File ret = new File(root);
    for (String part : parts) {
        ret = new File(ret,part);
    }
    return ret;
}

Then you can use:

File f = SomeUtilityClass.newFile("some","path","file.ext");

(this may exist in the recent JRE, but if so, I don't know where it is.)

If you only need something suitable for FileInputStream, etc., I may just hard code the forward slash for two reasons:

>They are easier to read than backslashes > they will also work on other operating systems

Either way, I may still create a file because it gives clearer values Most IO APIs in Java accept files in place - and it makes all the surrounding code obvious that this is a file path So you can use:

File file = new FIle("some/path/file.ext");

... this still applies to windows You can then use file Getcanonicalfile to get the specification. If you like, you can use backslash instead of forward slash