This code works:

public final class Foo
{
    private static final List<String> INPUTS = Arrays.asList(
        "/foo", "//foo", "foo/", "foo/bar", "foo/bar/../baz", "foo//bar"
    );

    public static void main(final String... args)
    {
        Path path;

        for (final String input: INPUTS) {
            path = Paths.get("/", input).normalize();
            System.out.printf("%s -> %s\n", input, path);
        }
    }
}

Output:

/foo -> /foo
//foo -> /foo
foo/ -> /foo
foo/bar -> /foo/bar
foo/bar/../baz -> /foo/baz
foo//bar -> /foo/bar

NOTE however that this is NOT portable. It won't work on Windows machines...

If you want a portable solution you can use memoryfilesystem, open a Unix filesystem and use that:

try (
    final FileSystem fs = MemoryFileSystem.newLinux().build();
) {
    // path operations here
}

Because the normalization replaced the .. programs' parent directory.

So you have NIO2 as a sub-folder of OCPJP7.

Similarly, . goes away as it's redundant (indicates current directory within context).

Use the built-in String method replaceAll, with a regular expression "/+", replacing one or more slashes with one slash:

path = path.replaceAll("/+", "/");