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Re: Unexpected Boxing Error at Runtime

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Dear All,

Thanks for the many responses. Woa,
the situation is quite contrived,

I looked at the byte code, and it seems
that it is translated as:

     public int getNodesCount() {
         synchronized (this) {
        return (children != null ? Integer.valueOf(
                       children.size()) : null).intValue();
     }

So ut seems the if-then-else to gets some type
widening from <nulltype> to Integer.

This makes it impossible for the compiler to spot
the error. Because usually this is spotted:

         int foo = null;

     Error: java: incompatible types: <nulltype>
     cannot be converted to int

Best Regards

P.S.:
Here is the byte code of the if-then-else expression.
The compiler was javac 1.8.0_152:

     GETFIELD DomElement.children : ListArray;
     IFNULL L5
     ALOAD 0
     GETFIELD DomElement.children : ListArray;
     INVOKEVIRTUAL ListArray.size ()I
     INVOKESTATIC java/lang/Integer.valueOf (I)Ljava/lang/Integer;
     GOTO L6
    L5
     ACONST_NULL
    L6
     INVOKEVIRTUAL java/lang/Integer.intValue ()I

j4n bur53 schrieb:
> Dear All,
> 
> By accident I used the following code:
> 
>      public int getNodesCount() {
>          synchronized (this) {
>              return (children != null ? children.size() : null);
>          }
>      }
> 
> It has a subtle error, namely it returns a primitive
> data type, i.e. 'int', but uses automatic boxing.
> 
> But that 'null' cannot be boxed to 'int', is only
> detected at runtime, and not during compile time.
> 
> Is this a bug or feature of Java?

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Unexpected Boxing Error at Runtime j4n bur53 <janburse@fastmail.fm> - 2018-01-04 15:16 +0100
  Re: Unexpected Boxing Error at Runtime Eric Douglas <e.d.programmer@gmail.com> - 2018-01-04 07:04 -0800
  Re: Unexpected Boxing Error at Runtime Eric Sosman <esosman@comcast-dot-net.invalid> - 2018-01-04 10:13 -0500
  Re: Unexpected Boxing Error at Runtime Eric Douglas <e.d.programmer@gmail.com> - 2018-01-04 08:01 -0800
    Re: Unexpected Boxing Error at Runtime Marcel Mueller <news.5.maazl@spamgourmet.org> - 2018-01-04 18:33 +0100
      Re: Unexpected Boxing Error at Runtime Kiwi User <martin@mydomain.invalid> - 2018-01-04 19:29 +0000
    Re: Unexpected Boxing Error at Runtime Eric Sosman <esosman@comcast-dot-net.invalid> - 2018-01-04 15:09 -0500
      Re: Unexpected Boxing Error at Runtime Daniele Futtorovic <da.futt.news@laposte.net> - 2018-01-04 21:43 +0100
        Re: Unexpected Boxing Error at Runtime Arne Vajhøj <arne@vajhoej.dk> - 2018-01-04 15:53 -0500
          Re: Unexpected Boxing Error at Runtime Daniele Futtorovic <da.futt.news@laposte.net> - 2018-01-05 16:06 +0100
            Re: Unexpected Boxing Error at Runtime Gene Wirchenko <genew@telus.net> - 2018-01-05 09:51 -0800
              Re: Unexpected Boxing Error at Runtime Daniele Futtorovic <da.futt.news@laposte.net> - 2018-01-05 20:59 +0100
                Re: Unexpected Boxing Error at Runtime Eric Douglas <e.d.programmer@gmail.com> - 2018-01-05 12:15 -0800
                Re: Unexpected Boxing Error at Runtime Kiwi User <martin@mydomain.invalid> - 2018-01-05 21:52 +0000
                Re: Unexpected Boxing Error at Runtime Gene Wirchenko <genew@telus.net> - 2018-01-08 11:13 -0800
                Re: Unexpected Boxing Error at Runtime Eric Sosman <esosman@comcast-dot-net.invalid> - 2018-01-05 16:27 -0500
                Re: Unexpected Boxing Error at Runtime Daniele Futtorovic <da.futt.news@laposte.net> - 2018-01-06 00:06 +0100
                Re: Unexpected Boxing Error at Runtime Kiwi User <martin@mydomain.invalid> - 2018-01-05 23:57 +0000
                Re: Unexpected Boxing Error at Runtime Arne Vajhøj <arne@vajhoej.dk> - 2018-01-07 20:06 -0500
                Re: Unexpected Boxing Error at Runtime bursejan@gmail.com - 2018-01-08 04:10 -0800
                Re: Unexpected Boxing Error at Runtime bursejan@gmail.com - 2018-01-08 04:31 -0800
                Re: Unexpected Boxing Error at Runtime Daniele Futtorovic <da.futt.news@laposte.net> - 2018-01-08 16:25 +0100
                Re: Unexpected Boxing Error at Runtime Arne Vajhøj <arne@vajhoej.dk> - 2018-01-08 20:05 -0500
                Re: Unexpected Boxing Error at Runtime bursejan@gmail.com - 2018-01-08 17:55 -0800
                Re: Unexpected Boxing Error at Runtime Gene Wirchenko <genew@telus.net> - 2018-01-08 11:19 -0800
                Re: Unexpected Boxing Error at Runtime Daniele Futtorovic <da.futt.news@laposte.net> - 2018-01-08 20:40 +0100
                Re: Unexpected Boxing Error at Runtime Gene Wirchenko <genew@telus.net> - 2018-01-08 18:03 -0800
                Re: Unexpected Boxing Error at Runtime Daniele Futtorovic <da.futt.news@laposte.net> - 2018-01-16 02:33 +0100
                Re: Unexpected Boxing Error at Runtime bursejan@gmail.com - 2018-01-22 14:26 -0800
                Re: Unexpected Boxing Error at Runtime bursejan@gmail.com - 2018-01-22 14:33 -0800
        Re: Unexpected Boxing Error at Runtime Arne Vajhøj <arne@vajhoej.dk> - 2018-01-04 19:16 -0500
          Re: Unexpected Boxing Error at Runtime Kiwi User <martin@mydomain.invalid> - 2018-01-05 12:17 +0000
  Re: Unexpected Boxing Error at Runtime j4n bur53 <janburse@fastmail.fm> - 2018-01-05 00:13 +0100
    Re: Unexpected Boxing Error at Runtime Eric Sosman <esosman@comcast-dot-net.invalid> - 2018-01-05 11:05 -0500
      Re: Unexpected Boxing Error at Runtime bursejan@gmail.com - 2018-01-06 06:18 -0800

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