Set question

[Arad Chear]

  
   public static void main(String ... args){
      Set<Number> s=new TreeSet<Number>();
       s.add(1);
       s.add(3.2);//error why ? 
   }
 
  

since Double is-a Number

[Keith Lynn]

Yes, Double is a Number. But the elements of a TreeSet have to be mutually comparable.

[Arad Chear]

thanks so much lynn ,i got it

[m ali]

Hi Keith,

But we are declaring here the collection as type-safe number. Integer is a Number and Double is a Number? Why the above code fail to compile? please explain?

Thanks in advance.

[Chandra Bhatt]

public static void main(String ... args){
      Set<Number> s=new TreeSet<Number>();
       s.add(1);
       s.add(3.2);//error why ? 
   }

No, Ali, Did you compile the above code?
This code compiles fine but gives runtime exception because
of mutual incomparability between treeset objects. One object
is Integer and another is Double.

TreeSet uses Comparable interface's compareTo(...) method that
is implemented by the objects inserted into, tokeep the objects
in sorted manner. And an Integer and an Double can't be compared
because they are not mutually comparable as Keith said
already.




Regards,
cmbhatt
[ April 24, 2007: Message edited by: Chandra Bhatt ]

[m ali]

Thank you Chandra,

I got it.

[Zhao zhenhua]

Thanks ,Chandra Bhatt.Yes!You are right!