Simple Code? What's Wrong?

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Peter van der Goes - 14 Jul 2005 00:33 GMT

It's probably something obvious, but this has me stumped:

Very simple code extracted from a proper main()

int x = 65;
int y = 55;

if (x > y)
int ans = x + y;

Errors:
E:\CIT1613\HelloWorld.java:17: '.class' expected
int ans = x + y;
^
E:\CIT1613\HelloWorld.java:17: not a statement
int ans = x + y;

Line 17 is int ans = x + y;

?!?

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Mike Schilling - 14 Jul 2005 01:19 GMT

> It's probably something obvious, but this has me stumped:
>
[quoted text clipped - 14 lines]
>
> Line 17 is int ans = x + y;

You can't declare a variable here. In JLS-speak:

Statement : if ParExpression Statement [else Statement]

and while a LocalVariableDeclarationStatement can appear in a Block, it
isn't itself a Statement. (Which argues it should be called something else
, but ...)

Likewise

if (x > y)
label: x = y;

and

if (x > y)
class Inner { .....}

are also forbidden.

int ans;
if (x > y)
ans = x + y;

is of course OK.

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Peter van der Goes - 14 Jul 2005 02:56 GMT

> You can't declare a variable here. In JLS-speak:
>
[quoted text clipped - 21 lines]
>
> is of course OK.

Thanks very much for the explanation. I don't think this is well known, at
least not by textbook authors (one of whom used this code in a test question
bank, indicating the correct answer is: ans = 120).
A local variable declaration with initialization not a statement.
Interesting. Same code works fine in C++, but that's not pertinent.
As your explanation suggests, adding {} will allow the code to compile.
I learned something today. I appreciate you taking the time...

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Mike Schilling - 14 Jul 2005 20:15 GMT

> Thanks very much for the explanation. I don't think this is well known, at
> least not by textbook authors (one of whom used this code in a test
> question bank, indicating the correct answer is: ans = 120).
> A local variable declaration with initialization not a statement.

Certainly it's a statement in the normal use of that term, but it's not a
Statement in the JLS's Backus-Naur grammar.

> Interesting. Same code works fine in C++, but that's not pertinent.

That's a really bad idea, I would think.

i = 0;
if (i > 0)
int ans = 12;

if (ans > 0) // is ans declared here? If so, what is its value?

But C++, unlike Java, has no rules to force variables to be initialized
before they're used.

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Roedy Green - 14 Jul 2005 02:53 GMT

>if (x > y)
> int ans = x + y;

spelling that out longhand

if ( x > y )
{

int ans = x + y;

}

your error should be more obvious. You create ans then instantly throw
it away.

you mean to write something like this:

int ans = ( x > y) ? x + y : x - y;

or

int ans = y;

if ( x > y )
{
ans = 42;
}

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Simple Code? What's Wrong?

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