Why use Java. Net in Java security. Can securitymanager read any file?

I just want to read and write some files in my java program So I use Java security. Security manager to manage it, but it doesn't seem satisfactory

Main. The java file is as follows

import java.io.*;
import java.util.*;
public class Main {
    static private final String INPUT = "in.txt";
    public static void main(String args[]) throws Exception {
        FileInputStream instream = null;
        BufferedReader reader = new BufferedReader(new FileReader(INPUT));
        String tempString = null;
        while ((tempString = reader.readLine()) != null) {
            System.out.println(tempString);
        }
    }
}

And file / opt / Java The policy is as follows

grant {
    permission java.io.FilePermission "./out.txt","write";
};

Then I ran away

java -Xss64m -Xms16m -Xmx512m -Djava.security.manager -Djava.security.policy=/opt/java.policy Main

But there is no error, the output is in txt. I tried other files and got the same results Why is that?

Solution

From Javadoc:

This is not to say that it is clear The code is not in the "directory": it is executed from the current working directory, which seems to mean