java - not able to use the comparator in my program -

in program not identifying compartor, don't want use compareto.

class testtreeset {     public static void main(string args[])     {         buildobject build = new buildobject();         treeset treeset = new treeset( new compared());         treeset = build.sendastreeset();         iterator itr = treeset.iterator();         while(itr.hasnext())         {             obj object = (obj) itr.next();             system.out.println(object.getname() + "\n " + object.getage() + "\n "                  + object.getsalary());         }     } } 

this comparator

class compared implements comparator {     public int compare(object , object b)     {         obj 1 = (obj) a;         obj 2 = (obj) b;         double salaryone = one.getsalary();         double salarytwo = two.getsalary();         int ageone = one.getage();         int agetwo = two.getage();         if( ageone == agetwo)         {             if(salaryone > salarytwo)             {                 return -1;             }             else if(salaryone < salarytwo)             {                 return 1;             }             else return 0;         }         else if(ageone > agetwo)         return -1;         else return 1;     } } 

what problem ? shows cannot cast java.lang.comparable exception

since use

treeset treeset = new treeset(); 

in sendastreeset method, treeset tries sort elements added using theire natural ordering. witch impiles class of objects musst implement compareable interface.

you should replace line with

treeset treeset = new treeset( new compared()); 

the same line in main method can removed.