Why are these classes equal? Loaded from different classloaders.

Question

I thought that classes loaded from different classloaders were seen as different in the JVM? But this code prints true to every check:
try
     Class c = new URLClassLoader( new URL[] { new URL( "jar:file://home/tests/test.jar!/" ) } ).loadClass( "Test" );
     Class c2 = new URLClassLoader( new URL[] { new URL( "jar:file://home/tests/test.jar!/" ) } ).loadClass( "Test" );
     System.out.println( ( c == c2 ) );
     System.out.println( ( c.equals( c2 ) ) );
     System.out.println( ( c.getName().equals( c2.getName() ) ) );
catch (Exception e)
     e.printStackTrace();
}

Answer 1

DrClap wrote:
The more unbelievable thing is that this:
System.out.println( ( c == c2 ) );prints "true". That shouldn't happen, and it's nothing to do with facts about classloaders. It shouldn't happen because "new" called twice should produce two different objects, no matter what kind of objects they are.
I didn't try your code because I would have had to spend a couple of minutes creating suitable jar files. But did you actually run that code? Or is it a reduction of some larger piece of code and you just assumed it would do what you said it does? Because I don't believe that.I actually ran the code and every line DID print out true. This is in Java 1.5.
I figured out why they're all true though - it's because the jar file was in the classpath, so the classes were loaded by a different classloader (the same one). When I put the jar out of the classpath, the statments printed out like this:
//false
System.out.println( ( c == c2 ) );
//false
System.out.println( ( c.equals( c2 ) ) );
//true
System.out.println( ( c.getName().equals( c2.getName() ) ) );I agree on the first one printing true but I seem to remember something about how they changed that rule in Java 1.5. I could be wrong but in c++, that would be a completely valid true statement (assuming your class implemented the "==" operator), so maybe they changed it to be in line with that?