How to Sort a List of Objects by Multiple Properties in Java

How can I sort a List of objects in Java based on multiple properties?

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

In Java, sorting a list of objects by multiple properties can be efficiently accomplished using the `Comparator` interface. This method allows you to chain comparators for a multi-level sort, enabling you to sort by one property and then by others as needed.

import java.util.*;

public class Main {
    public static void main(String[] args) {
        List<ActiveAlarm> alarms = new ArrayList<>();
        // Add active alarms to the list
        Collections.sort(alarms, Comparator.comparingLong((ActiveAlarm a) -> a.timeStarted)
                                               .thenComparingLong(a -> a.timeEnded));
    }
}

Causes

• Inconsistent sorting due to lack of a clear strategy for handling ties between the primary and secondary sorting properties.
• Using the wrong sorting methods or failing to implement the Comparator interface correctly.

Solutions

• Implement a Comparator to define the sorting logic for the list.
• Use the Collections.sort() method or stream's sorted() method with the created Comparator.

Mistake: Not implementing the Comparator properly, leading to incorrect sorting results.

Solution: Ensure you're using the correct syntax for creating the Comparator, and test with sample data.

Mistake: Forgetting to handle null values in your properties, which can cause NullPointerExceptions.

Solution: Add null checks in your comparator logic to ensure robust sorting.