JLS8 section 4.2.5 conversion of integer/float expressions and references to boolean values

[Florian.Wiedenmann at grob.de]

Hello!

I have a question regarding chapter 4.2.5 of the current specification JLS8.

The last passage of page 51 and the first one on page 52 refer to the conversion of float and int expressions as well as object references to a boolean value. I have never heard or seen that before and I'm not able to reproduce that behavior with jdk1.8.0_25 (out of date - I know ;) ).

I have tried the following statements:

// the float expression 0.55f - 0.33f  is not converted to a boolean value - i.e. the entire expression cannot be evaluated
// compiler message:
// error: incompatible types: float cannot be converted to boolean
boolean b = 0.55f - 0.33f ? true : false;

// trying to assign a float value to a boolean variable
// compiler message:
// error: incompatible types: float cannot be converted to boolean
boolean b = 0.55f;

// trying to assign a float expression to a boolean variable:
// error: incompatible types: float cannot be converted to boolean
boolean b = 0.55f - 0.33f;


// trying to convert a new reference to boolean:
// incompatible types: Object cannot be converted to boolean
boolean b = new Object();

// trying reference conversion in expression:
// error: incompatible types: Object cannot be converted to boolean
boolean b = new Object() ? true : false;

Now I'm wondering if I misunderstood the passage (which is likely - I'm not exactly an expert) or whether it's implementation specific (maybe it works with OpenJDK?). In any case I think that behaviour is not very clear - any of the conversions can easily be written as a Boolean expression which tells the reader exactly what it does (e.g. new Object() != null ? true : false). I guess it has been added as a concession to C developers.

I'd be really happy to hear from you!

Greetings from Germany ;)

Best regards,
Florian Wiedenmann



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