using relativize() method

[Puspender Tanwar]

my current directory is : C:\myprograms
we have some rules for this method:
1. using relativize() to construct a path between a two absolute paths having different roots (say, C:\ and D:\) would throw IlliegalArgumentException.
2. using relativize() to construct a path between absolute path and relative path would throw IlliegalArgumentException.
Ok that's a rule. I agree. But what if say :

Path p1 = Paths.get("/java");
System.out.println(p1.toAbsolutePath()); // will print C:\java
Path p2 = Paths.get("C:/io/IO.txt");
p1.relativize(p2); // throws [tt]IlliegalArgumentException[/tt]

now my question is this, since the line1 proves that the path is an absolute path and line2 proves that it is under the Root C:\ . Both these fulfills the conditions required as i mentions above in point 1 and 2 . Both paths are absolute and both belongs to the same Root i.e C:\ . Then why IlliegalArgumentException ?

[Ahmed Bin S]

Please read documentation before posting.

https://docs.oracle.com/javase/7/docs/api/java/nio/file/Path.html#relativize%28java.nio.file.Path%29

A relative path cannot be constructed if only one of the paths have a root component. Where both paths have a root component then it is implementation dependent if a relative path can be constructed.

So change /java to C:/java and it will work. The fact that toAbsolutePath() gives C:\java is irrelevant.

[Puspender Tanwar]

I agree with the documentation

Ahmed Bin S wrote:
So change /java to C:/java and it will work. The fact that toAbsolutePath() gives C:\java is irrelevant.

I know it will work .
But that irrelevant C:\java is also a valid place in memory . we can easily store file to this irrelevant place.
Then why relativize() consider the two paths different , one having C:\ and one without C:\. As my question is ?

[Ahmed Bin S]

It's a design decision. The designers make decisions so that the language is easy to use and to reduce the probability of errors - allegedly!

You have to realise that neither toAbsolutePath() nor relativize() check the actual path+file exist. See below. If they don't care whether it exists or not, then it is irrelevant that you actually have a C:\java on your system.

These methods operate at the "logical" and not the "physical" level. If you want to use relativize() then it is up to you to create a Path object so that it is C:\java, and then call relativize() on that.

import java.nio.file.*;

public class Test {

	public static void main(String[] args){
		Path p1 = Paths.get("C:/a/b");
		System.out.println("Absolute path of p1: "+ p1.toAbsolutePath());
		Path p2 = Paths.get("C:/a/b/c/d");
		System.out.println("Absolute path of p2: "+ p2.toAbsolutePath());
		System.out.println("Relative path of p2 to p1: " + p1.relativize(p2).toString());
	}

}

U1@Ahmed MINGW64 ~
$ java Test
Absolute path of p1: C:\a\b
Absolute path of p2: C:\a\b\c\d
Relative path of p2 to p1: c\d

U1@Ahmed MINGW64 ~
$ ls -ld C:/a/b
ls: cannot access C:/a/b: No such file or directory

U1@Ahmed MINGW64 ~
$ ls -ld C:/a/b/c/d
ls: cannot access C:/a/b/c/d: No such file or directory