Difference between Comparator and Comparable in java

Comparable interface:

Class whose objects to be sorted must implement this interface.In this,we have to implement compareTo(Object) method.

For example:

public class Country implements Comparable<Country>{  
 @Override
 public int compareTo(Country country) {  
       return (this.countryId < country.countryId ) ? -1: (this.countryId > country.countryId ) ? 1:0 ;  
 }}  

If any class implements comparable inteface then collection of that object can be sorted automatically using Collection.sort() or Arrays.sort().Object will be sort on the basis of compareTo method in that class.
Objects which implement Comparable in java can be used as keys in a SortedMap like TreeMap or SortedSet like TreeSet without implementing any other interface.

Comparator interface:

Class whose objects to be sorted do not need to implement this interface.Some third class can implement this interface to sort.E.g.CountrySortByIdComparator class can implement Comparator interface to sort collection of country object by id.

         Country indiaCountry=new Country(1, "India");  
         Country chinaCountry=new Country(4, "China");  
         Country nepalCountry=new Country(3, "Nepal");  
         Country bhutanCountry=new Country(2, "Bhutan");           

         List<Country> listOfCountries = new ArrayList<Country>(); 
         listOfCountries.add(indiaCountry);  
         listOfCountries.add(chinaCountry);  
         listOfCountries.add(nepalCountry);  
         listOfCountries.add(bhutanCountry);   
 
 //Sort by countryName  

           Collections.sort(listOfCountries,new Comparator<Country>() {  
                @Override 
                public int compare(Country o1, Country o2) {
                    return o1.getCountryName().compareTo(o2.getCountryName());  }  
            });