Sort List<T> of objects by a particular rule?

问题

I have this list:

List<Country> countryList = new ArrayList<Country>();

And I want to sort the countries by their name, by using the method getCountry(). How can achieve this?

UPDATE:

public class Country implements Comparable
@Override
public int compareTo(Object another) {
    // TODO Auto-generated method stub
    return 0;
}

Can you tell how to compare them to get it sorted by Strings? Argentina, Austria, Brazil, etc.

回答1:

There are two ways:

1. Have Country implement the java.util.Comparable interface to define a natural ordering on your Country objects, i.e. make the objects themselves "know" their ordering. You can then use Collections.sort(List) or just switch from your List to a SortedSet implementation like TreeSet (if you don't need duplicates, a Set drops duplicates)

2. Write a java.util.Comparator to define an imposed ordering and call Collections.sort(List, Comparator) or (losing duplicates again) go for a new TreeSet(Comparator).

Implementing one of these two is enough to solve your problem -- both Comparable and Comparator can be combined, though: using a Comparator will override any natural ordering defined by Comparable.

回答2:

You can call Collections.sort() providing a Comparator which compares the getCountry().

回答3:

Use the built in sort method and make sure you implement comparable on Country

来源：https://stackoverflow.com/questions/7776822/sort-listt-of-objects-by-a-particular-rule