where need to use collections.sort() and comparable and comparator interfaces in java collection? -

i got understanding of collections gone through articles.
'm confusing should implement collections.sort() method , need use comparable interface(compareto() , comparator interface (compare()).

comparable interface compare , reference object comparator compare 2 objects.

i know situation need use methods ?

thanks,

you should not implement collections.sort(); method built-in java. call method without supplying comparator sort natural order, if it's comparable. else, supply comparator sort comparator's way.

you should have class implement comparable , provide compareto method if class has natural ordering, indicated in comparable javadocs. example integer , double, have natural mathematical ordering.

you should create class implements comparator when cannot make class of object sort comparable or when want present ordering alternative natural ordering, or when want impose order when there no natural ordering. example reverse natural order (say, sort descending, largest smallest). example data object multiple fields, want sortable on multiple fields, e.g. person object firstname , lastname: have comparator sorts on lastname first, , sorts on firstname first.