Starting with the 9/21 Merlin nightly build (i.e. due to a change integrated subsequent to promoted build 80), it appears that URL objects created from File.toURL are not correctly reported as equal to equivalent URL objects constructed from the URL(String) constructor. The following test case demonstrates the bug:

import java.io.*;
import java.net.*;

public class URLEquals {
    public static void main(String[] args) throws Exception {
File f0 = new File(args[0]);
URL u0 = f0.toURL();
System.err.println("\nu0: " + u0);

File f1 = new File(args[0]);
URL u1 = f1.toURL();
System.err.println("\nu1: " + u1);
showEquals("u0", u0, "u1", u1);

String s1 = u1.toExternalForm();
URL u2 = new URL(s1);
System.err.println("\nu2: " + u2);
showEquals("u1", u1, "u2", u2);

String s2 = u2.toExternalForm();
URL u3 = new URL(s2);
System.err.println("\nu3: " + u3);
showEquals("u2", u2, "u3", u3);
    }

    private static void showEquals(String n1, Object o1,
String n2, Object o2)
    {
System.err.println(n1 + ".equals(" + n2 + ") returns " +
(o1.equals(o2) ? "TRUE" : "FALSE"));
System.err.println(n2 + ".equals(" + n1 + ") returns " +
(o2.equals(o1) ? "TRUE" : "FALSE"));
    }
}

It produces the following result when run against the 9/21 nightly Merlin build (and the 9/22 and 9/23 nightly builds as well):

[terrier] 236 % which java
/net/mizu.sfbay/usr/re/jdk/jdk1.4/binaries/solsparc/b81-2001-09-21/j2sdk1.4.0/bin/java
[terrier] 237 % java -version
java version "1.4.0-beta3"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.0-beta3-b81)
Java HotSpot(TM) Client VM (build 1.4.0-beta3-b81, mixed mode)
[terrier] 238 % java URLEquals .

u0: file:/tmp/./

u1: file:/tmp/./
u0.equals(u1) returns TRUE
u1.equals(u0) returns TRUE

u2: file:/tmp/./
u1.equals(u2) returns FALSE
u2.equals(u1) returns FALSE

u3: file:/tmp/./
u2.equals(u3) returns TRUE
u3.equals(u2) returns TRUE

[See Comments for further speculation.]