inheritance in java - simple question - Java

"Thomas" <arabel9@o2.pl> writes:
> List (two directions )
> / \
> / \
> Queue Stack
>The thing is List has more methods than Q and S.

»Q« and »S« were not mentioned before.

interface Stack { ... }
interface Queue { ... }
interface List extends Stack, Queue { ... }

class ArrayList implements List { ... }
class ArrayStack implements Stack { ... }
class ArrayQueue implements Queue { ... }

And thus spoke Thomas...

> The thing is List has more methods than Q and S. Should I make the methods,
> which aren't common private or use the interface mechanism ? Are there other
> ways two do that model inheritence in java ?

Why is that so? What methods do you think List should have? Are we
talking about the java.util.list interface here or do you want to
implement something different?

Flo

Thomas wrote:
> I have to implement a simple class hierarchy :
>
>
> List (two directions )
> / \
> / \
> Queue Stack
>
> The thing is List has more methods than Q and S. Should I make the methods,
> which aren't common private or use the interface mechanism ? Are there other
> ways two do that model inheritence in java ?
>
>

You cannot reduce an inherited method from public to private, because
that breaks the superclass contract.

Why extend List at all?

You could write a class Queue that has exactly the methods you think a
queue should have, no more and no less. Have a List reference as an
instance variable and implement the Queue methods by manipulating your List.

Similarly, a Stack implementation could use a List reference to do most
of the work, without extending List.

Patricia

Flo 'Irian' Schaetz <iryan@gmx.de> writes:
>Are we talking about the java.util.list interface here

public class Main
{ public static void main( final java.lang.String[] args )
{ java.lang.System.out.println( java.util.list.class ); }}

javac Main.java
Main.java:3: cannot find symbol
symbol : class list
location: package java.util
{ java.lang.System.out.println( java.util.list.class ); }}
^
1 error

Uzytkownik "Patricia Shanahan" <pats@acm.org> napisal w wiadomosci
news:3xtli.6930$Od7.4456@newsread1.news.pas.earthlink.net...
> Thomas wrote:
> > I have to implement a simple class hierarchy :
> >
> >
> > List (two directions )
> > / \
> > / \
> > Queue Stack
> >
> > The thing is List has more methods than Q and S. Should I make the
methods,
> > which aren't common private or use the interface mechanism ? Are there
other
> > ways two do that model inheritence in java ?
> >
> >
>
> You cannot reduce an inherited method from public to private, because
> that breaks the superclass contract.
>
> Why extend List at all?
>
> You could write a class Queue that has exactly the methods you think a
> queue should have, no more and no less. Have a List reference as an
> instance variable and implement the Queue methods by manipulating your
List.
>
> Similarly, a Stack implementation could use a List reference to do most
> of the work, without extending List.
>
> Patricia


ok thx Yes, this might be a solution, but the constraints about the
hierarchy I gave are still for that lab (I; m a student . As i remember
in c++ i had had to write the same. Then i just extended the classes as
above, override the useless methods to empty method {} and C&P the others
needed (since i dont have the code, i dont rembember I did the last one).
Just wondering isn't any more elegant solution to do this.

Thomas wrote:
> Uzytkownik "Patricia Shanahan" <pats@acm.org> napisal w wiadomosci
> news:3xtli.6930$Od7.4456@newsread1.news.pas.earthlink.net...
>> Thomas wrote:
>>> I have to implement a simple class hierarchy :
>>>
>>>
>>> List (two directions )
>>> / \
>>> / \
>>> Queue Stack
>>>
>>> The thing is List has more methods than Q and S. Should I make the
> methods,
>>> which aren't common private or use the interface mechanism ? Are there
> other
>>> ways two do that model inheritence in java ?
>>>
>>>
>> You cannot reduce an inherited method from public to private, because
>> that breaks the superclass contract.
>>
>> Why extend List at all?
>>
>> You could write a class Queue that has exactly the methods you think a
>> queue should have, no more and no less. Have a List reference as an
>> instance variable and implement the Queue methods by manipulating your
> List.
>> Similarly, a Stack implementation could use a List reference to do most
>> of the work, without extending List.
>>
>> Patricia
>
>
> ok thx Yes, this might be a solution, but the constraints about the
> hierarchy I gave are still for that lab (I; m a student . As i remember
> in c++ i had had to write the same. Then i just extended the classes as
> above, override the useless methods to empty method {} and C&P the others
> needed (since i dont have the code, i dont rembember I did the last one).
> Just wondering isn't any more elegant solution to do this.
>
>

OK - you have to conform to lab exercise requirements.

A couple of comments:

There is a specific exception, java.lang.UnsupportedOperationException,
that is thrown e.g. by java.util collection classes to indicate that an
operation is defined in a superclass or interface, but not supported in
this particular implementation. I would throw that from any method that
you are implementing only because of the badly designed inheritance
hierarchy.

There should be no need to copy and paste - any method that is declared
public in List will be available in both Stack and Queue.

Patricia