array bounds

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Mark - 27 Nov 2005 01:05 GMT

Scanner scan = new Scanner(System.in);
String cmd[] = scan.nextLine().split("\\s");

if( cmd[0].equals("use") )
{
if( cmd[1] != null )
// do some crap
else
// do something else
}

so basically, if the user just types "use" it will "do something else",
but if he enters a parameter... it will.. use it.

but just by calling if( cmd[1] != null ) if a 2nd parameter isnt
given.. and throws an error..

wait.. that's it isnt it? i should just catch it, instead of checking
if its null?

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Lee Weiner - 27 Nov 2005 01:36 GMT

>Scanner scan = new Scanner(System.in);
>String cmd[] = scan.nextLine().split("\\s");
[quoted text clipped - 15 lines]
>wait.. that's it isnt it? i should just catch it, instead of checking
>if its null?

No, you should check the length of the array returned from split() to see how
many parameters were passed.

Lee Weiner
lee AT leeweiner DOT org

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Mark - 27 Nov 2005 01:43 GMT

lol.. why didnt i think of that?

but thats... well. i was going to say more annoying but not really.

oh well. my method works well enough.

though somehow deliberately relying on throwing exceptions.. not as an
error, but as an "else"... doesnt sound like proper coding.

anyways, thanks.

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zero - 27 Nov 2005 12:35 GMT

"Mark" <mnbayazit@gmail.com> wrote in news:1133055788.702467.301260
@f14g2000cwb.googlegroups.com:

> though somehow deliberately relying on throwing exceptions.. not as an
> error, but as an "else"... doesnt sound like proper coding.

It isn't - exceptions should be exceptional, not the rule. There is a lot
of overhead involved with exceptions (even more if you have finally), so
you should avoid using them for normal program flow.

Signature

Beware the False Authority Syndrome

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Roedy Green - 27 Nov 2005 06:16 GMT

>wait.. that's it isnt it? i should just catch it, instead of checking
>if its null?

you probably want:

if ( cmd.length > 1 && cmd[1] != null && cmd[1].length() > 0 )

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Canadian Mind Products, Roedy Green.
http://mindprod.com Java custom programming, consulting and coaching.

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Thomas Hawtin - 27 Nov 2005 14:10 GMT

>>wait.. that's it isnt it? i should just catch it, instead of checking
>>if its null?
>
> you probably want:
>
> if ( cmd.length > 1 && cmd[1] != null && cmd[1].length() > 0 )

String/Pattern.split does not return arrays containing nulls. So the
null check is misleading.

For me str.length() != 0 (or !str.equals("")) is clearer than
str.length() > 0. In 1.6 it can be replaced by !str.isEmpty(). My guess
in this case is that an empty string might point up some input sequences
not considered.

Tom Hawtin

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Unemployed English Java programmer
http://jroller.com/page/tackline/

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Roedy Green - 27 Nov 2005 18:11 GMT

On Sun, 27 Nov 2005 14:16:42 +0000, Thomas Hawtin
<usenet@tackline.plus.com> wrote, quoted or indirectly quoted someone
who said :

>For me str.length() != 0 (or !str.equals("")) is clearer than
>str.length() > 0.

But you don't want negative length strings, even if there were such a
thing. You want something with characters in it.

!str.equals("") implies you are avoiding some particular value.

It seems in general better to specify what you do want than what you
don't. Of course which feels natural then flows from the choice you
made in the deep past. It feels natural because that's your idiomatic
way of doing it.

My choice would originally have been influenced by an understanding of
the implementation. str.length()>0 will compile better code even on a
stupid compiler/runtime.

Signature

Canadian Mind Products, Roedy Green.
http://mindprod.com Java custom programming, consulting and coaching.

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Thomas Hawtin - 27 Nov 2005 18:40 GMT

> On Sun, 27 Nov 2005 14:16:42 +0000, Thomas Hawtin
> <usenet@tackline.plus.com> wrote, quoted or indirectly quoted someone
[quoted text clipped - 5 lines]
> But you don't want negative length strings, even if there were such a
> thing. You want something with characters in it.

I want to be quite clear that String.length never returns any special
values...

> !str.equals("") implies you are avoiding some particular value.

...and that I am avoiding one particular value of string.

Tom Hawtin

Signature

Unemployed English Java programmer
http://jroller.com/page/tackline/

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Mark - 02 Dec 2005 02:38 GMT

well. lee's solution was quite alright.
thank you guys :p

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array bounds

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