Sort an ArrayList base on multiple attributes

Question

I have an ArrayList of object. The object contain attributes date and value. So I want to sort the objects on the date, and for all objects in the same date I want to sort them on value. How can I do that?

Answer 1

Implement a custom Comparator, then use Collections.sort(List, Comparator). It will probably look something like this:

public class FooComparator implements Comparator<Foo> {
    public int compare(Foo a, Foo b) {
        int dateComparison = a.date.compareTo(b.date);
        return dateComparison == 0 ? a.value.compareTo(b.value) : dateComparison;
    }
}

Collections.sort(foos, new FooComparator());

Answer 2

public static <T> void sort(List<T> list, final List<Comparator<T>> comparatorList) {  
       if (comparatorList.isEmpty()) {//Always equals, if no Comparator.  
            throw new IllegalArgumentException("comparatorList is empty.");  
       }  
       Comparator<T> comparator = new Comparator<T>() {  
       public int compare(T o1, T o2) {  
               for (Comparator<T> c:comparatorList) {  
                   if (c.compare(o1, o2) > 0) {  
                     return 1;  
                   } else if (c.compare(o1, o2) < 0) {  
                     return -1;  
                   }  
               }  
               return 0;  
         }  
       };  
       Collections.sort(list, comparator);  
  }