Hello Vijay..
you need to understand this line in broader way.. let me explain some..
above code will help you to understand your question..
See in Client code i have did sorting 3 time..
one natural using comparable
2nd using comparator
3rd using comparator - reverse order
but if you consider way one.. and i want to change my sorting criteria i must have to change the
test class
but if i do same thing using comparator - then i just need to introduce new comparator.. but it`s client side code no need to change original class...