"." In the file path, new file (".")

Today, when I look at thinking in Java, I find this line of code: 
File File = new file (".");

At first I was very puzzled and didn't understand this "." What does it mean? 
later, after some experiments returned: 
"." Knowledge represents the current working directory, it is the writing of a relative path, typically the JVM call path, which can be
obtained by System.getproperty ("User.dir")
. 
If you write this:
File File = new file ("..");

Represents the upper-level directory where the User.dir is obtained. 
The final summary is as follows: 
"." The current working directory, which is User.dir, is equivalent to ". \ \", which is the
file File = new file (".");
With the
file File = new file (". \ \");
is equivalent. 
".." Represents the User.dir upper directory, with the ".. \ \ "Equivalence