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I've got a problem similar to the one already posted here. The validator does not believe I'm using the relativize() method of the Path class. I'm wondering why. I also have another question, not related to the validation process. The tasks "hints" that if I can't find the relative path between path1 and path2, I should try to find the relative path between path2 and path1. I'm checking for that with the if-else statement (and the validator agrees that my program displays the relative path between the entered paths, if it exists) but I'm not sure that this idea of mine is really good. The thing is, there is no method like "ifRelative()" or "ifRelativePathExists()", so I decided to use !(...).ifAbsolute() and also check for a null input just in case (idk if there can be a null at all in this case). Was that really worth doing?

Write a program that reads two paths from the keyboard and displays the relative path between these paths, if it exists. Otherwise, don't display anything.

Hint: If you couldn't find the relative path between path1 and path2, then try to find the relative path between path2 and path1.

Requirements:

The program should read two paths from the console.
The program should display the relative path between the entered paths, if it exists.
To calculate the relative path, the relativize() method of the Path class should be used.
Do not use the following classes: File, FileInputStream, FileOutputStream, FileReader, FileWriter (of the java.io package).

package en.codegym.task.pro.task15.task1514; import java.nio.file.Path; import java.util.Scanner; /* It's all relative */ public class Solution { public static void main(String[] args) throws IllegalArgumentException { Scanner scanner = new Scanner(System.in); String str1 = scanner.nextLine(); String str2 = scanner.nextLine(); Path path1 = Path.of(str1); Path path2 = Path.of(str2); Path result = path1.relativize(path2); if (!result.isAbsolute() && result !=null) System.out.println(result); else { result = path2.relativize(path1); if (!result.isAbsolute() && result !=null) System.out.println(result); } } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

10 June, 13:38

Thomas's answer is correct and should help you solve this, but I do have a little bit to add about what he said here: "If result would be really null, then isAbsolute would throw a NullPointerException before you reach that check." I notice in your code that you do this quite often, where you check for null values after calling a method on a variable. When a variable is null there is no object connected to it and ANY use of that variable will result in a NullPointerException being thrown. Therefore when null checks are required then they should occur first in your code before proceeding further. Take this small example:

// String test = null;
String test = "something";

System.out.print("Vairable test is: ");
if(test.isEmpty() && test != null)
    System.out.println("initialized");
else System.out.println("null");

If you run this it will work just fine. However if you uncomment the first line and comment the second one and run it again the program will crash with a null pointer exception as expected because when test is null then .isEmpty() method is called on that and the exception occurs. So to fix the example code I shared you only have to do the null check first:

if(test != null && test.isEmpty())

Thomas

Level 41 , Bayreuth, Germany

10 June, 09:46

Why the validator doesn't recognize relativize... idk, guessing now. 1. You may want to try Paths.get(String) instead of Path.of(String) (because the latter didn't exist in 1.8). But I think they upgraded JDK version to 13 for pro and you said it recognizes relativize if you add conditions? That leads me to another probability: 2. Put relativize in a try block and catch the exception (read below for more info). In the catch block output nothing, do nothing, just ignore. Or you try the b.relativize(a) in that catch block (the CG hint).. and if that throws, too, then you output nothing... but imho that is superfluous If a.relativize(b) returns a valid path, then b.relativize(a) will also. Example (I used the one from the docs): /a/b /a/b/c/d 1. result: c/d 2. result ../.. If you feed it with invalid arguments (when it can not build a rel. path) then it throws an exception. Just check the docs: Throws: IllegalArgumentException - if other is not a Path that can be relativized against this path It never gives back an absolute path and also not null (again from the docs:) Returns: the resulting relative path, or an empty path if both paths are equal The null check is totally redundant. If result would be really null, then isAbsolute would throw a NullPointerException before you reach that check. And isAbsolute... as said, relativize always returns a Path or throws an exception.

Evgeniia Shabaeva

Level 27 , Budapest, Hungary

17 June, 10:10

Thank you very much! Instead of the if-clauses, I wrote

try {
System.out.println(path1.relativize(path2));
} catch (Exception e) {
    System.out.println(path2.relativize(path1));
}

And that passed)