Using Comparator in Java for Sorting
Java's Comparator interface is a powerful tool for customizing the sorting behavior of collection objects. It makes it easy to sort data according to specific criteria, beyond the default Comparable interface.
Understanding the Comparator Interface
The Comparator interface defines a single method, compare(), which takes two objects and returns an integer:
Usage of Comparator
To use a Comparator with a collection, simply pass an instance of the Comparator as the second argument to collection sorting methods such as Collections.sort(). For example:
List<MyObject> myObjects = new ArrayList<>(); Collections.sort(myObjects, new MyComparator());
Where MyComparator implements the Comparator
Resolving the ClassCastException
In the code you provided, the Exception in thread "main" java.lang.ClassCastException error occurs because your People class implements the Comparator interface instead of Comparable. To resolve this issue, remove the implements Comparator line from the People class.
A separate Comparator class should be created to handle the sorting logic. For instance:
public class PeopleComparator implements Comparator<People> { @Override public int compare(People p1, People p2) { return p1.getId() - p2.getId(); } }
And use it as follows:
Collections.sort(peps, new PeopleComparator());
Additional Notes
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