Possible ClassCastException in java.util.regex.Pattern.BmpCharPredicate#union(java.util.regex.Pattern.CharPredicate...)

[Pavel Rappo]

Has that method been ever used? If nothing else its name seems strange. To me, a union has OR semantics, not AND.

> On 27 Aug 2021, at 15:37, Andrey Turbanov <turbanoff at gmail.com> wrote:
> 
> Hello.
> I found suspicious code in the method
> "java.util.regex.Pattern.BmpCharPredicate#union(java.util.regex.Pattern.CharPredicate...)"
> https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/java/util/regex/Pattern.java#L5639
> 
> static CharPredicate union(CharPredicate... predicates) {
>    CharPredicate cp = ch -> {
>        for (CharPredicate p : predicates) {
>            if (!p.is(ch))
>                return false;
>        }
>        return true;
>    };
>    for (CharPredicate p : predicates) {
>        if (! (p instanceof BmpCharPredicate))
>            return cp;
>    }
>    return (BmpCharPredicate)cp;
> }
> 
> Variable `cp` has type CharPredicate initially. And then it's casted
> to BmpCharPredicate. This cast always fails with ClassCastException
> when reached.
> 
> Can reproduced in small sample class:
> 
>    public static void main(String[] args) {
>        CharPredicate result = BmpCharPredicate.union();
>        System.out.println(result);
>    }
> 
>    interface CharPredicate {
>        boolean is(int ch);
>    }
> 
>    interface BmpCharPredicate extends CharPredicate {
>        static CharPredicate union(CharPredicate... predicates) {
>            CharPredicate cp = ch -> true;
>            for (CharPredicate p : predicates) {
>                if (! (p instanceof BmpCharPredicate))
>                    return cp;
>            }
>            return (BmpCharPredicate)cp;
>        }
>    }
> 
> 
> Exception in thread "main" java.lang.ClassCastException: class
> org.RegexpBug$BmpCharPredicate$$Lambda$14/0x0000000800c028f0 cannot be
> cast to class org.RegexpBug$BmpCharPredicate
> (org.RegexpBug$BmpCharPredicate$$Lambda$14/0x0000000800c028f0 and
> org.RegexpBug$BmpCharPredicate are in unnamed module of loader 'app')
>    at org.RegexpBug$BmpCharPredicate.union(RegexpBug.java:20)
>    at org.RegexpBug.main(RegexpBug.java:5)
> 
> As I can see this method is never used. Perhaps it should be removed?
> 
> 
> Andrey Turbanov