Sorting an Array List of Objects based on a variable in object

Question

I have an Array List of Objects

The objects in the Array List are information for college called 'ModuleInfo' (course, assignments, dateDue )

The dateDue has been formatted into an integer YYYYMMDD (From a calendar)

I've looked at some of the other ways people have done this, but I can't get my head around what it is that I need to do.

Ideally because I've already stated when creating the Array List that it will contain 'ModuleInfo' objects I could just Collection.sort(moduleDB, ModuleInfo.getDateDue) or something along those lines. moduleDB being the Array List

Any help would be much appreciated.

Answer 1

If you want to use Collections.sort(List list) to sort your list, your object must implement the Comparable interface.

public class ModuleInfo implements Comparable<ModuleInfo> {

    /* Your implementation */

    public int compareTo(ModuleInfo info) {
        if (this.dateDue < info.dateDue) {
            return -1;
        } else if (this.dateDue > info.dateDue) {
            return 1;
        } else {
            return 0;
        }
    }
}

Then call Collections.sort(moduleDB) where moduleDB has type ArrayList<ModuleInfo> .

ps As mentioned in a previous post, you can also have your class implement the Comparator interface to achieve identical results.