Every example I find is about doing this alphabetically, while I need my elements sorted by date.
My ArrayList contains objects on which one of the datamembers is a DateTime object. On DateTime I can call the functions:
lt() // less-than
lteq() // less-than-or-equal-to
So to compare I could do something like:
if(myList.get(i).lt(myList.get(j))){
// ...
}
What should I do inside the if block?
You can use Collections.sort method. It's a static method. You pass it the list and a comparator. It uses a modified mergesort algorithm over the list. That's why you must pass it a comparator to do the pair comparisons.
Collections.sort(myList, new Comparator<MyObject> {
public int compare(MyObject o1, MyObject o2) {
DateTime a = o1.getDateTime();
DateTime b = o2.getDateTime();
if (a.lt(b))
return -1;
else if (a.lteq(b)) // it's equals
return 0;
else
return 1;
}
});
Note that if myList is of a comparable type (one that implements Comparable interface) (like Date, Integer or String) you can omit the comparator and the natural ordering will be used.