Need reviewer for forward port of 6815768 (File.getXXXSpace) and 6815768 (String.hashCode)

[Ulf Zibis]

Am 26.02.2010 12:52, schrieb Dmitry Nadezhin:
> I found two alternatives in the link
> http://mail.openjdk.java.net/pipermail/coin-dev/2009-December/002618.html
>    
> The first alternative
> int equalByHashThreshold = 2;
>
> public boolean equals(Object anObject) {
>    if (this == anObject) {
>      return true;
>    }
>    if (anObject instanceof String) {
>
>      String anotherString = (String)anObject;
>      int n = count;
>      if (n == anotherString.count&&
>          (equalByHashThreshold == 0 || --equalByHashThreshold == 0)&&
>          (anotherString.equalByHashThreshold == 0 || --anotherString.equalByHashThreshold == 0)&&
>
>
>          hash() == anotherString.hash()) {
> [snipped]
>      }
>    }
>    return false;
> }
>    
>
> will say that
> "A".equals("A") == false
> because body of if statement will not be executed

I don't understand your problem.
1. String literals are always interned, so "A" is always identical to 
"A". Therefore the body of the 1st if will return true.
2. If the strings are not identical, body of 2nd if will be executed, if 
anObject is instance of String.

>
> The second alternative
> public int hashCode() {
>    int h = hash;
>    if (h == 0 || --h == 0) {
>      int off = offset;
>      char val[] = value;
>      int len = count;
>
>
>
>      for (int i = 0; i<  len; i++) {
>        h = 31*h + val[off++];
>      }
>      hash = h;
>    }
>    return h;
> }
>    
> will return sequentially
>
> "A".hashCode() == 65
> "A".hashCode() == 64
> "A".hashCode() == 64
> . . .

You are right. Good catch.

So better:

public int hashCode() {
   int h = hash;
   if (h == 0) {
     int len = count;
     if (len>  0) {
       char[] val = value;
       for (int i = 0, off = offset; i<  len; i++)
         h = 31*h + val[off++];
       hash = h;
     }
   } else if (h == 1) {
     hash = 0;
     return hashCode();
   }
   return h;
}


- Ulf