How to sort List of objects by some property

Question

I have simple class

public class ActiveAlarm {
    public long timeStarted;
    public long timeEnded;
    private String name = "";
    private String description = "";
    private String event;
    private boolean live = false;
}

and List<ActiveAlarm> con. How to sort in ascending order by timeStarted, then by timeEnded? Can anybody help? I know in C++ with generic algorithm and overload operator <, but I am new to Java.

Answer 1

Using Comparator

For Example:

class Score {

    private String name;
    private List<Integer> scores;
    // +accessor methods
}

---

    Collections.sort(scores, new Comparator<Score>() {

        public int compare(Score o1, Score o2) {
            // compare two instance of `Score` and return `int` as result.
            return o2.getScores().get(0).compareTo(o1.getScores().get(0));
        }
    });

With Java 8 onwards, you can simply use lambda expression to represent Comparator instance.

Collections.sort(scores, (s1, s2) -> { /* compute and return int */ });