another bit of trickery-dickery

[JosAH]

Since it's so quiet overhere: what will happen when this snippet is executed?

[code=java]
String s = "000A003B";
if (true == false) // "s" will be changed later to \u000A\u003B
System.out.prin tln("boo");
[/code]
I just read this one somewhere else and I like it ;-)

kind regards,

Jos

[Laharl]

I'm assuming there's more to this snippet, having just executed it and had nothing print, as expected.

[BigDaddyLH]

Since it's so quiet overhere: what will happen when this snippet is executed?

[code=java]
String s = "000A003B";
if (true == false) // "s" will be changed later to \u000A\u003B
System.out.prin tln("boo");
[/code]
I just read this one somewhere else and I like it ;-)

kind regards,

Jos

My compiler warned me :-(

[BigDaddyLH]

Here's another, copied from Java Puzzlers:
[CODE=Java]public class Outer {
class Inner1 extends Outer {}
class Inner2 extends Inner1 {}
}[/CODE]
That won’t compile. Why not? Explain. How can you fix it?

[Laharl]

Inner classes need extra syntax, if my memory serves, something involving };.

[BigDaddyLH]

Inner classes need extra syntax, if my memory serves, something involving };.

Do you mean "};" -- a semicolon after a certain close-brace? No, you are thinking of anonymous class syntax:

[CODE=Java]ClassName x = new ClassName() {
public void f() {}
};[/CODE]

and there the "};" syntax is really a special case of
[CODE=Java]ClassName x = expression ;//<<--[/CODE]

[JosAH]

I'm assuming there's more to this snippet, having just executed it and had nothing print, as expected.

Your compiler must be broken then.

kind regards,

Jos

[JosAH]

Here's another, copied from Java Puzzlers:
[CODE=Java]public class Outer {
class Inner1 extends Outer {}
class Inner2 extends Inner1 {}
}[/CODE]
That won’t compile. Why not? Explain. How can you fix it?

If you make the Inner1 class a static class it compiles but it ruins the intended
class structure ;-)

kind regards,

Jos

[BigDaddyLH]

If you make the Inner1 class a static class it compiles but it ruins the intended
class structure ;-)

kind regards,

Jos

Here's Joshua Bloch's and Neal Gafter's explanation (it's puzzle #9):

http://www.javapuzzlers.com/java-puzzlers-sampler.pdf

[JosAH]

Here's Joshua Bloch's and Neal Gafter's explanation (it's puzzle #9):

http://www.javapuzzlers.com/java-puzzlers-sampler.pdf

I understand; my 'solution' just got rid of the entire problem by not needing that
sort of unknown Outer instantiation needed by that Inner2 constructor. For now
I find their solution a bit of a language deficiency but I can't be a discussion
partner in that issue yet: I find it filthy ;-)

Ok, now what about the riddle I transmogrified from Sun's forum to this one?
No (correct) answers yet ;-)

kind regards,

Jos

[Laharl]

Your compiler must be broken then.

kind regards,

Jos

I tried it again and...there are indeed shenanigans involved. Not only did the expected 'unreachable statement' compiler warning not appear, but 'boo' was printed. No clue why, though...

[sukatoa]

I tried it again and...there are indeed shenanigans involved. Not only did the expected 'unreachable statement' compiler warning not appear, but 'boo' was printed. No clue why, though...

Me too... no warnings....
Whenever i swap those boolean literals, nothings happen(boo printed)....
i've changed "000A003B" to new String("000A003 B"), nothings changed....

i changed the comment, boo not printed... i removed \u000A\u003B, boo not printed....

So, is \u000A\u003B is not really part of the comment? since they are line feed and a semicolon, is \u000A\u003B are acceptable statement in java?..

because, when i put a brace inside of it

if(true==false) {// "s" will be changed later to \u000A\u003B
System.out.prin tln("boo");
}

boo doesn't print....

[JosAH]

Me too... no warnings....
Whenever i swap those boolean literals, nothings happen(boo printed)....
i've changed "000A003B" to new String("000A003 B"), nothings changed....

i changed the comment, boo not printed... i removed \u000A\u003B, boo not printed....

So, is \u000A\u003B is not really part of the comment? since they are line feed and a semicolon, is \u000A\u003B are acceptable statement in java?..

because, when i put a brace inside of it

if(true==false) {// "s" will be changed later to \u000A\u003B
System.out.prin tln("boo");
}

boo doesn't print....

You're very close; the answer from the JLS (Java Language Specification)

3.2 Lexical Translations
A raw Unicode character stream is translated into a sequence of tokens, using the following three lexical translation steps, which are applied in turn:

A translation of Unicode escapes (§3.3) in the raw stream of Unicode characters to the corresponding Unicode character. A Unicode escape of the form \uxxxx, where xxxx is a hexadecimal value, represents the UTF-16 code unit whose encoding is xxxx. This translation step allows any program to be expressed using only ASCII characters.

So first the raw input stream is analyzed and any \uxxxx sequence of characters
(xxxx == four hexadecimal nibbles) is translated to its Unicode character. So
the code:

[code=java]
// blahblah \u000a\u003b
[/code]

is translated as:

[code=java]
// blahblah
;
[/code]

Note that \u000a is translated to a newline character and \u003b is translated to
a semi colon. The semicolon effectively ends the nonsensical if statement in the
original example and that's why "boo" is printed (the entire print statement is
not part of the if-statement anymore although to human readers it looks like it is).

kind regards,

Jos