Re: String.equals optimisation

[Archie Cobbs]

Simon Kitching wrote:.
> * Class.getName returns strings that have been interned. I don't
>   think this is explicitly required by the java specs but is
>   certainly true for Sun's JVM and seems likely to be done by
>   any sensible JVM.

You definitely make some good arguments, but this one is not
neccesarily true. In fact, I'd argue a JVM that interns every
class' name (even if only on demand) is potentially wasting
a bunch of heap space.

I.e., is there something special about class names which means
they should be treated differently from any other String randomly
created and used in a Java application? (rhetorical question)
Otherwise, why not intern all Strings? Etc.

In any case, to provide two concrete counter-examples:

  $ cat > zz.java
  public class zz {
    public static void main(String[] args) {
        zz z = new zz();
        System.out.println(z.getClass().getName() == "zz");
    }
  }
  $ javac zz.java
  $ java zz
  true
  $ jc -Xint zz
  false
  $ jamvm zz
  false

On the other hand, comparing reference equality is very low cost,
so it seems like adding "==" to equals() might make good sense.

Of course, the "real" answer lies in empirical testing (something
I can't claim to have done).

-Archie

__________________________________________________________________________
Archie Cobbs      *        CTO, Awarix        *      http://www.awarix.com