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Ouch	September 22, 2006

I've just gotten my first bite mark from primitive auto-boxing in Java 1.5. The following code is meant to read a file in either special mode or non-special mode, or to auto-detect special-ness if the boolean argument is null. This would (correctly) be a compile error in 1.4.2:


void readFile(String filename, Boolean isSpecial) {

    if (!isSpecial) // OUCH

        readFile(filename, autodetectSpecial(filename));

    } else {

        readFile(filename, isSpecial.booleanValue());

    }

}

The problem should be that I'm checking "isSpecial" for null without explicitly comparing it to null--- this is a mistake I make when I switch back and forth between Javascript and Java a lot.

But in Java 1.5 this code compiles without complaint because the compiler thinks I meant to auto-dereference the boolean and check its value for falseness. And then at runtime I get a nice shiny NullPointerException when the auto-boxing logic attempts to dereference "isSpecial" and read its value as a boolean.

I'm not saying that auto-boxing is terrible, but it is an example of how it can bite you, and it's not 100% gravy.

Posted by rus at 02:15 PM

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