import java.util.Comparator; public class GeometricObjectComparator implements Comparator<GeometricObject>, java.io.Serializable { public int compare(GeometricObject o1, GeometricObject o2) { double area1 = o1.getArea(); double area2 = o2.getArea(); if (area1 < area2) return -1; else if (area1 == area2) return 0; else return 1; } }