java - Why object of number can be added in TreeSet -

the object of class want add treeset, class must implement comparable interface number class not implement comparable how treeset allow number added.

    number n1= 11;     number n2= 12;     number n3= 13;     set<number> set = new treeset<>();     set.add(n1);     set.add(n2);     set.add(n3); 

you right

class must implement comparable interface.

and here in example above statement valid. number has child class integer , when this:

 number n1= 11; 

on runtime create integer object , integer implement comparable.

you can see in java doc. here

or can proof program this:

number n1 = 10; system.out.println(n1 instanceof number);   //true   system.out.println(n1 instanceof integer);  //true   system.out.println(n1 instanceof comparable);   //true   

hope help!