null

triggerthat · 3 Feb 2006 at 17:55

Hi guys,

Just abit stuck on something. Basically I've got an array of IDs. I've got a if statement that checks that student doesn’t have a mark already.

Basically I have -

marks[num] != null;

Obviously you can't apply null to a int type so I was wondering how'd you do it?

kbc · 3 Feb 2006 at 18:06

triggerthat said:
Hi guys,

Just abit stuck on something. Basically I've got an array of IDs. I've got a if statement that checks that student doesn’t have a mark already.

Basically I have -

marks[num] != null;

Obviously you can't apply null to a int type so I was wondering how'd you do it?

Would it not be:

marks[num] != 0;

toastyman · 3 Feb 2006 at 18:07

What language is it?

It could be marks[num]!==NULL;

triggerthat · 3 Feb 2006 at 18:11

Hey,

It's Java. You can't applied null to int.

And as for != 0, it wont work for the first entry considering my num index will start at 0.

kbc · 3 Feb 2006 at 18:16

triggerthat said:
Hey,

It's Java. You can't applied null to int.

And as for != 0, it wont work for the first entry considering my num index will start at 0.

You mean an empty mark is indicated by the integer "0" ?

Cold_And_Miserable · 3 Feb 2006 at 18:33

In C++ an empty piece of a string is indicated by '/0'.

Lagz · 3 Feb 2006 at 18:43

int values MUST always have a value in Java. Just initialise your array so they are all set to something you will never use (eg: -1) and then do if(mark!=-1).

Alternatively use an Integer[] rather than an int[]. Integer is basically an object which just wraps an int (at least, it was last time I looked). Since Integers are objects they can be null.

triggerthat · 3 Feb 2006 at 18:52

Hi,

Unfortunately the specification states that they have to of type int, and we have to define the index as 0.

Basically I just have to check the array of marks doesn’t have a mark already.

Visage · 4 Feb 2006 at 10:09

Why not define a new type, NulableInt, that contains an int and a Null flag?

NullableInt i ;

....code that gets a puils mark snipped....

if ( i.IsNull() )
{
...do something...
}
else
{
int pupils_mark - i.value() // i.value returns the stored int
}

Lagz · 4 Feb 2006 at 10:32

That would be just the same as using the Integer class, but defining it yourself!

D.P. · 4 Feb 2006 at 11:40

triggerthat said:
Hey,

It's Java. You can't applied null to int.

And as for != 0, it wont work for the first entry considering my num index will start at 0.

just init your array to -1 values and check against that.