Collections.sort() in Java 5

[alex_us01]

hello,

Probably has a simple solution but I couldn't see it.
I still get an "unchecked" warning for this:

---
ArrayList<Decision> alDec = new ArrayList<Decision>();
...
// By the way, Decision implements Comparable interface
...
Collections.sort(alDecs); // here I get the unchecked warning
---

What am I missing?

thanks,
alex

[Thomas Hawtin]

alex_us01 wrote:
>
> Probably has a simple solution but I couldn't see it.
> I still get an "unchecked" warning for this:
>
> ---
> ArrayList<Decision> alDec = new ArrayList<Decision>();
> ...
> // By the way, Decision implements Comparable interface
> ...
> Collections.sort(alDecs); // here I get the unchecked warning

^^^^^^ It's alDec above.

> ---
>
> What am I missing?

o The actual code you tried to compile, preferably as a short,
complete, compilable example.
o The actual error given.
o Details of the Decision type.

I guess the error message is something like:

Dec.java:6: warning: [unchecked] unchecked method invocation:
<T>sort(java.util.List<T>) in java.util.Collections is applied to
(java.util.ArrayList<Decision>)
Collections.sort(alDecs);
^
1 warning

Note, javac doesn't tell us what the problem was. But if I reveal the
Decision class I broke to force the error:

abstract class Decision implements Comparable { }

There's your problem. The Comparable interface takes a generic
parameter, which is missing.

abstract class Decision implements Comparable<Decision> { }

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

[Ronny Schuetz]

alex_us01 wrote:

Decision needs to implement Comparable<Decision> instead of
Comparable.

[alex_us01]

Sorry, that was my typo when writing it here. It is alDecs in both
places and don't have problem compiling it. Thanks.
alex

[alex_us01]

Thanks!! That was it: Decision needs to implement Comparable<Decision>.
I didn't think about this, I really appreciate it!

alex

[Roedy Green]

On 16 Oct 2005 06:09:54 -0700, "alex_us01" <aris...@gmail.com> wrote
or quoted :

>ArrayList<Decision> alDec = new ArrayList<Decision>();
>...
>// By the way, Decision implements Comparable interface
>...
>Collections.sort(alDecs); // here I get the unchecked warning
>-

You sail alDec in the first line and alDecs in the second.

Your Comparable needs to be generified too. See
http://mindprod.com/jgloss/sort.html
http://mindprod.com/jgloss/comparable.html
--
Canadian Mind Products, Roedy Green.
http://mindprod.com Again taking new Java programming contracts.