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From: Ross on 6 Jul 2010 11:30
Let's say that I have a java.util.ArrayList which will contain only
strings. So, I can declare this as:

ArrayList<String> blah = new ArrayList<String>();

So far so good, but let's say that blah is an array in itself. I'd
expect to be able to do this:

ArrayList<String> blah[] = new ArrayList<String>[ 50 ];

However, if I do that, I get a compile time error saying something
about creating a generic array. If I modify the code to:

ArrayList<String> blah[] = new ArrayList[ 50 ];

Then, it compiles and works, but gives me a warning about using a
deprecated blah blah blah.

What gives?
From: Lew on 6 Jul 2010 12:20
Ross wrote:
> Let's say that I have a java.util.ArrayList which will contain only
> strings. So, I can declare this as:
>
> ArrayList<String> blah = new ArrayList<String>();
>
> So far so good, but let's say that blah is an array in itself. I'd
> expect to be able to do this:
>
> ArrayList<String> blah[] = new ArrayList<String>[ 50 ];
>
> However, if I do that, I get a compile time error saying something
> about creating a generic array. If I modify the code to:
>
> ArrayList<String> blah[] = new ArrayList[ 50 ];
>
> Then, it compiles and works, but gives me a warning about using a
> deprecated blah blah blah.
>
> What gives?

Arrays and generics don't mix. It has to do with arrays being
reifiable but not generics.

From the JLS, §10.10:
"... creation of arrays of non-reifiable types is forbidden."
<http://java.sun.com/docs/books/jls/third_edition/html/
arrays.html#10.10>

--
Lew
From: markspace on 6 Jul 2010 12:23
It's a pain but Java's generics are not reifiable. Simple solution:
prefer ArrayList to arrays:


ArrayList<ArrayList<String>> arrayOfLists =
new ArrayList<ArrayList<String>>( 50 );

arrayOfLists.add( new ArrayList<String>() );

etc.
From: Lew on 6 Jul 2010 12:29
markspace wrote:
> It's a pain but Java's generics are not reifiable.  Simple solution:
> prefer ArrayList to arrays:
>
>    ArrayList<ArrayList<String>> arrayOfLists =
>        new ArrayList<ArrayList<String>>( 50 );
>
>    arrayOfLists.add( new ArrayList<String>() );
>
> etc.

Prefer Lists of Lists to ArrayLists of ArrayLists:

List <List <String>> holyOfHolies =
new ArrayList <List <String>> ();

holyOfHolies.add( new ArrayList <String> () );

--
Lew
From: Mike Schilling on 6 Jul 2010 13:18


"Lew" <lew(a)lewscanon.com> wrote in message
news:f4a6bdb8-c41e-4978-9abf-70e5791f87f5(a)c33g2000yqm.googlegroups.com...
> Ross wrote:
>> Let's say that I have a java.util.ArrayList which will contain only
>> strings. So, I can declare this as:
>>
>> ArrayList<String> blah = new ArrayList<String>();
>>
>> So far so good, but let's say that blah is an array in itself. I'd
>> expect to be able to do this:
>>
>> ArrayList<String> blah[] = new ArrayList<String>[ 50 ];
>>
>> However, if I do that, I get a compile time error saying something
>> about creating a generic array. If I modify the code to:
>>
>> ArrayList<String> blah[] = new ArrayList[ 50 ];
>>
>> Then, it compiles and works, but gives me a warning about using a
>> deprecated blah blah blah.
>>
>> What gives?
>
> Arrays and generics don't mix. It has to do with arrays being
> reifiable but not generics.
>
> From the JLS, �10.10:
> "... creation of arrays of non-reifiable types is forbidden."
> <http://java.sun.com/docs/books/jls/third_edition/html/
> arrays.html#10.10>

There aren't many instances in Java of "That's how it works. Don't ask why;
you're better off not knowing", but this is one of them.

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