Mock Exam Question

[Asha Pathik]

hi,

import java.util.*;
class test implements Comparator < test >
{
int testNumber;
public static void main( String args[] )
{
Set < test > s1 = new TreeSet < test > ();

s1.add(new test());
s1.add(new test());
 
}
public int compare( test t1 , test t2 )
{
return t1.testNumber - t2.testNumber;
}
 
}
 

Choose 3 that apply.
 
a.Compiles without warnings
b.Compiles with warnings
c.Only one test Object is added, the other one is considered a duplicate.
d.A Runtime Exception occurs.
e.TreeSet can only accept objects of type test. ( Given that test has no sub classes )
    

In the above code the answers are given as " a, d and e". I understood the reson for option a and d but I'm not able to get why option e is correct. Could someone plz explain me that?

Thanks

[Keith Lynn]

That is the purpose of the generic declaration TreeSet<test>. You specify that the TreeSet is going to hold test objects.

[Asha Pathik]

Oh! ... got it. It was a general question about generics. I was mixing it with program behaviour.

Thanks Keith
Asha

[Dave Tan]

Is the use of the Comparator interface allowed? As far as i know, only interface Comparable can be used.

[Keith Lynn]

Do you mean in general or with generics?

[Asha Pathik]

I meant the other options were related to the program behaviour whereas the last option was about the correct meaning of the "generic collection declaration", nothing related to program behaviour.

Asha